[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"log-posts-page-1":3,"log-categories":2172,"log-applications":2182},{"posts":4,"totalPages":24},[5,152,247,313,404,491,590,694,765,855,946,1032,1118,1204,1291,1379,1466,1552,1651,1737,1825,1911,1996,2082],{"id":6,"date":7,"date_gmt":8,"guid":9,"modified":11,"modified_gmt":12,"slug":13,"status":14,"type":15,"link":16,"title":17,"content":19,"excerpt":22,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":30,"categories":31,"application":33,"class_list":34,"acf":41,"_links":105},693,"2025-11-25T17:37:26","2025-11-25T22:37:26",{"rendered":10},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=693","2026-01-26T11:59:09","2026-01-26T16:59:09","marine-magnetics-next-generation-synapse-magnetometer-validates-seamless-integration-with-eivas-scanfish-katria-rotv","publish","post","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2025\u002F11\u002F25\u002Fmarine-magnetics-next-generation-synapse-magnetometer-validates-seamless-integration-with-eivas-scanfish-katria-rotv\u002F",{"rendered":18},"Marine Magnetics Next-Generation Synapse Magnetometer Validates Seamless Integration with EIVA’s ScanFish Katria ROTV",{"rendered":20,"protected":21},"\u003Cp>Toronto ON, November 25 2025 — Marine Magnetics, a leader in ultra-high-sensitivity marine magnetometry, announced the seamless integration and compatibility with EIVA’s ScanFish Katria intelligent Remotely Operated Towed Vehicle (ROTV) solution. This collaboration delivers a significantly simplified and ultra-efficient tool for high-speed detection of sub-bottom magnetic anomalies.\u003C\u002Fp>\n\u003Cp>Synapse represents continual advancements of Marine Magnetics’ advanced magnetometers, built around next-generation laser-driven optically pumped magnetometer technology. Synapse continues to offer high-speed sampling up to 20 Hz, a lightweight design (2.5kg), and ultra-low power consumption. In addition to its integrated long-distance networkable telemetry, it now incorporates an additional dedicated RS232 interface, facilitating significantly easier integration into AUV and ROTV platforms.\u003C\u002Fp>\n\u003Cp>The new sensor also adds smart array configuration and synchronization capabilities, further enhancing its performance in multi-sensor setups.\u003C\u002Fp>\n\u003Cp>EIVA’s ScanFish Katria is recognized as an intelligent wide-sweep ROTV, engineered for time-efficient surveys. It offers a versatile platform for a wide range of magnetometer survey applications. When paired with the high-sensitivity, low-power (4.5W to 7W) Synapse magnetometer, it unlocks maximum target-detection efficiency, providing a complete solution for rapid, reliable sub-bottom hazard and feature mapping.\u003C\u002Fp>\n\u003Ch4>About Marine Magnetics\u003C\u002Fh4>\n\u003Cp>Marine Magnetics is the world’s leading manufacturer of Overhauser magnetometers for marine applications. Their commitment to innovation delivers rugged, reliable, and high-performance solutions for deep-sea surveys, pipeline and cable tracking, and UXO detection.\u003C\u002Fp>\n\u003Ch4>About EIVA\u003C\u002Fh4>\n\u003Cp>EIVA is a global leading provider of software, equipment, and integrated system solutions for the offshore and shallow water survey, construction, and inspection industries. EIVA’s hardware portfolio includes the intelligent ScanFish ROTV series, enhancing efficiency across numerous maritime operations.\u003C\u002Fp>\n",false,{"rendered":23,"protected":21},"\u003Cp>This collaboration delivers a significantly simplified and ultra-efficient tool for high-speed detection of sub-bottom magnetic anomalies.\u003C\u002Fp>\n",1,0,"closed","open","","standard",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[32],13,[],[35,15,36,37,38,39,40],"post-693","type-post","status-publish","format-standard","hentry","category-news",{"external_link":28,"hero_media":42,"credits":101,"related_products":102},{"width":43,"height":44,"file":45,"filesize":46,"sizes":47,"image_meta":89,"original_image":98,"id":99,"url":100},2560,1679,"2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-scaled.jpg",986224,{"medium":48,"large":55,"thumbnail":61,"medium_large":66,"1536x1536":72,"2048x2048":78,"chip":84},{"file":49,"width":50,"height":51,"mime-type":52,"filesize":53,"url":54},"ScanFish-Katria-subsea_with-black-logo-300x197.jpg",300,197,"image\u002Fjpeg",34326,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-300x197.jpg",{"file":56,"width":57,"height":58,"mime-type":52,"filesize":59,"url":60},"ScanFish-Katria-subsea_with-black-logo-1024x672.jpg",1024,672,206770,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-1024x672.jpg",{"file":62,"width":63,"height":63,"mime-type":52,"filesize":64,"url":65},"ScanFish-Katria-subsea_with-black-logo-150x150.jpg",150,22722,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-150x150.jpg",{"file":67,"width":68,"height":69,"mime-type":52,"filesize":70,"url":71},"ScanFish-Katria-subsea_with-black-logo-768x504.jpg",768,504,127767,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-768x504.jpg",{"file":73,"width":74,"height":75,"mime-type":52,"filesize":76,"url":77},"ScanFish-Katria-subsea_with-black-logo-1536x1008.jpg",1536,1008,413823,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-1536x1008.jpg",{"file":79,"width":80,"height":81,"mime-type":52,"filesize":82,"url":83},"ScanFish-Katria-subsea_with-black-logo-2048x1344.jpg",2048,1344,677154,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-2048x1344.jpg",{"file":85,"width":86,"height":86,"mime-type":52,"filesize":87,"url":88},"ScanFish-Katria-subsea_with-black-logo-100x100.jpg",100,18549,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-100x100.jpg",{"aperture":90,"credit":28,"camera":91,"caption":28,"created_timestamp":92,"copyright":28,"focal_length":93,"iso":94,"shutter_speed":95,"title":28,"orientation":96,"keywords":97},"6.3","Canon EOS-1Ds Mark III","1351591159","70","320","0.003125","1",[],"ScanFish-Katria-subsea_with-black-logo.jpg",694,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FScanFish-Katria-subsea_with-black-logo-scaled.jpg","\u003Cp>Philip Suttak, Marine Magnetics, \u003Ca href=\"mailto:philip.suttak@marinemagnetics.com\" target=\"_blank\" rel=\"noopener noreferrer\">philip.suttak@marinemagnetics.com\u003C\u002Fa>,\u003Cbr \u002F>\nMartin Kristenswen, EIVA, \u003Ca class=\"autolinked\" href=\"mailto:mkr@eiva.com\" target=\"_blank\" rel=\"noopener noreferrer\" data-behavior=\"truncate\">mkr@eiva.com\u003C\u002Fa>\u003C\u002Fp>\n",[103,104],116,115,{"self":106,"collection":112,"about":115,"author":118,"replies":122,"version-history":125,"predecessor-version":129,"acf:post":133,"wp:attachment":138,"wp:term":141,"curies":148},[107],{"href":108,"targetHints":109},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F693",{"allow":110},[111],"GET",[113],{"href":114},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts",[116],{"href":117},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Ftypes\u002Fpost",[119],{"embeddable":120,"href":121},true,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fusers\u002F1",[123],{"embeddable":120,"href":124},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=693",[126],{"count":127,"href":128},3,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F693\u002Frevisions",[130],{"id":131,"href":132},805,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F693\u002Frevisions\u002F805",[134,136],{"embeddable":120,"href":135},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F115",{"embeddable":120,"href":137},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F116",[139],{"href":140},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=693",[142,145],{"taxonomy":143,"embeddable":120,"href":144},"category","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=693",{"taxonomy":146,"embeddable":120,"href":147},"application","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=693",[149],{"name":150,"href":151,"templated":120},"wp","https:\u002F\u002Fapi.w.org\u002F{rel}",{"id":153,"date":154,"date_gmt":155,"guid":156,"modified":158,"modified_gmt":159,"slug":160,"status":14,"type":15,"link":161,"title":162,"content":164,"excerpt":166,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":168,"categories":169,"application":170,"class_list":171,"acf":173,"_links":214},781,"2025-11-18T17:44:05","2025-11-18T22:44:05",{"rendered":157},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=781","2026-05-13T16:37:07","2026-05-13T20:37:07","announcing-our-official-youtube-channel","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2025\u002F11\u002F18\u002Fannouncing-our-official-youtube-channel\u002F",{"rendered":163},"Announcing Our Official YouTube Channel",{"rendered":165,"protected":21},"\u003Ch2>\u003Cstrong>We’re excited to announce the launch of the official Marine Magnetics YouTube channel, designed to be your primary resource for:\u003C\u002Fstrong>\u003C\u002Fh2>\n\u003Cul>\n\u003Cli>In-depth video tutorials\u003C\u002Fli>\n\u003Cli>Practical troubleshooting guides\u003C\u002Fli>\n\u003Cli>The latest product updates and announcements\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>We’ve already begun building a comprehensive library of videos and will be regularly adding new content. If there a specific topic, feature, or troubleshooting issue you’d like us to cover, \u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcontact\u002F\">let us know\u003C\u002Fa>!\u003C\u002Fp>\n\u003Cp>Subscribe and watch our videos: \u003Ca class=\"autolinked\" href=\"https:\u002F\u002Fwww.youtube.com\u002F@MarineMagnetics\" target=\"_blank\" rel=\"noopener noreferrer\" data-behavior=\"truncate\">https:\u002F\u002Fwww.youtube.com\u002F@MarineMagnetics\u003C\u002Fa>\u003C\u002Fp>\n",{"rendered":167,"protected":21},"\u003Cp>We’re excited to announce the launch of the official Marine Magnetics YouTube channel, designed to be your primary resource for: In-depth video tutorials Practical troubleshooting guides The latest product updates and announcements We’ve already begun building a comprehensive library of videos and will be regularly adding new content. If there a specific topic, feature, or […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[32],[],[172,15,36,37,38,39,40],"post-781",{"external_link":28,"hero_media":174,"credits":28,"related_products":28},{"width":175,"height":176,"file":177,"filesize":178,"sizes":179,"image_meta":209,"id":212,"url":213},1920,1080,"2025\u002F11\u002FYoutube-Announcement.png",465365,{"medium":180,"large":186,"thumbnail":191,"medium_large":195,"1536x1536":200,"chip":205},{"file":181,"width":50,"height":182,"mime-type":183,"filesize":184,"url":185},"Youtube-Announcement-300x169.png",169,"image\u002Fpng",20360,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement-300x169.png",{"file":187,"width":57,"height":188,"mime-type":183,"filesize":189,"url":190},"Youtube-Announcement-1024x576.png",576,161501,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement-1024x576.png",{"file":192,"width":63,"height":63,"mime-type":183,"filesize":193,"url":194},"Youtube-Announcement-150x150.png",15569,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement-150x150.png",{"file":196,"width":68,"height":197,"mime-type":183,"filesize":198,"url":199},"Youtube-Announcement-768x432.png",432,98203,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement-768x432.png",{"file":201,"width":74,"height":202,"mime-type":183,"filesize":203,"url":204},"Youtube-Announcement-1536x864.png",864,317697,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement-1536x864.png",{"file":206,"width":86,"height":86,"mime-type":183,"filesize":207,"url":208},"Youtube-Announcement-100x100.png",8234,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":211},"0",[],1111,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FYoutube-Announcement.png",{"self":215,"collection":220,"about":222,"author":224,"replies":226,"version-history":229,"predecessor-version":233,"wp:attachment":237,"wp:term":240,"curies":245},[216],{"href":217,"targetHints":218},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F781",{"allow":219},[111],[221],{"href":114},[223],{"href":117},[225],{"embeddable":120,"href":121},[227],{"embeddable":120,"href":228},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=781",[230],{"count":231,"href":232},7,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F781\u002Frevisions",[234],{"id":235,"href":236},1112,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F781\u002Frevisions\u002F1112",[238],{"href":239},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=781",[241,243],{"taxonomy":143,"embeddable":120,"href":242},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=781",{"taxonomy":146,"embeddable":120,"href":244},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=781",[246],{"name":150,"href":151,"templated":120},{"id":248,"date":249,"date_gmt":250,"guid":251,"modified":253,"modified_gmt":254,"slug":255,"status":14,"type":15,"link":256,"title":257,"content":259,"excerpt":261,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":263,"categories":264,"application":265,"class_list":266,"acf":268,"_links":280},1117,"2025-09-19T13:14:10","2025-09-19T17:14:10",{"rendered":252},"https:\u002F\u002Fnew.marinemagnetics.com\u002Fcms\u002F?p=1117","2026-05-19T13:18:41","2026-05-19T17:18:41","saying-goodbye-to-seaspy1","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2025\u002F09\u002F19\u002Fsaying-goodbye-to-seaspy1\u002F",{"rendered":258},"Saying goodbye to SeaSPY1 our original flagship magnetometer",{"rendered":260,"protected":21},"\u003Cdiv class=\"title-row\" data-v-ec1c5338=\"\">\n\u003Ch2 data-v-ec1c5338=\"\">SeaSPY1 Retirement Notice\u003C\u002Fh2>\n\u003C\u002Fdiv>\n\u003Cdiv class=\"content-html\" data-v-ec1c5338=\"\">\n\u003Cp>\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1110 size-medium\" src=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F09\u002FSeaSPY_reflect-web-300x121.png\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" srcset=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F09\u002FSeaSPY_reflect-web-300x121.png 300w, https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F09\u002FSeaSPY_reflect-web-1024x412.png 1024w, https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F09\u002FSeaSPY_reflect-web-768x309.png 768w, https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F09\u002FSeaSPY_reflect-web-1536x618.png 1536w, https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F09\u002FSeaSPY_reflect-web.png 1920w\" alt=\"\" width=\"300\" height=\"121\" \u002F>\u003C\u002Fp>\n\u003Cp>Dear customers,\u003C\u002Fp>\n\u003Cp>We have some big (bittersweet) news: It’s time for SeaSPY1, our original flagship magnetometer, to retire.\u003C\u002Fp>\n\u003Cp>Following 25 years of setting reliability, versatility, and efficacy standards, we’re retiring support of SeaSPY1, repairs and parts on January 1, 2026. SeaSPY2 will continue to enjoy our full support.\u003C\u002Fp>\n\u003Cp>The exciting part is that resources formerly dedicated to SeaSPY will now accelerate our already prolific innovation team. Thank you for being on this journey with us.\u003C\u002Fp>\n\u003Cp>There are exciting times ahead.\u003C\u002Fp>\n\u003C\u002Fdiv>\n",{"rendered":262,"protected":21},"\u003Cp>SeaSPY1 Retirement Notice Dear customers, We have some big (bittersweet) news: It’s time for SeaSPY1, our original flagship magnetometer, to retire. Following 25 years of setting reliability, versatility, and efficacy standards, we’re retiring support of SeaSPY1, repairs and parts on January 1, 2026. SeaSPY2 will continue to enjoy our full support. The exciting part is […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[32],[],[267,15,36,37,38,39,40],"post-1117",{"external_link":28,"hero_media":269,"credits":279,"related_products":28},{"bitrate":270,"filesize":271,"mime_type":272,"length":273,"length_formatted":274,"width":175,"height":176,"fileformat":275,"dataformat":276,"id":277,"url":278},3286581,3587714,"video\u002Fwebm",9,"0:09","webm","V_AV1",1073,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FDJI_0641-190720-Trim-sped.av1_.webm","\u003Cp>Magnetometer survey of the bay near Villa Rica for the Lost Ships of Cortes project, 2019. By Jonathan 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Underwater Explosive Ordinance Report (GICHD)",{"rendered":28,"protected":21},{"rendered":327,"protected":21},"\u003Cp>Geneva International Centre for Humanitarian Demining 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href=\"https:\u002F\u002Fmarinemagnetics.com\u002Finstall\u002Fsyfi\u002Fpublic\u002Fdefault.htm\">the latest Firmware Updater\u003C\u002Fa> now.\u003C\u002Fp>\n",{"rendered":418,"protected":21},"\u003Cp>Released 18 June, 2024, version 1.0.1.3 of Marine’s Firmware Updater enables you to update the transceiver firmware yourself to capitalize on our newest feature releases and critical updates. Compatible devices are: Synapse Synapse Horizontal Transverse Gradiometer Isolation Transceivers made after August, 2023 Sidescan Interface Transceivers for Synapse only, as of Spring 2024 Note: Sidescan Interface transceivers for SeaSPY […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[32],[],[423,15,36,37,38,39,40],"post-768",{"external_link":28,"hero_media":425,"credits":28,"related_products":453},{"width":340,"height":341,"file":426,"filesize":427,"sizes":428,"image_meta":449,"id":451,"url":452},"2024\u002F07\u002FDefault-Updater-1.png",14688,{"medium":429,"large":433,"thumbnail":437,"medium_large":441,"chip":445},{"file":430,"width":50,"height":347,"mime-type":183,"filesize":431,"url":432},"Default-Updater-1-300x200.png",2135,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FDefault-Updater-1-300x200.png",{"file":434,"width":57,"height":352,"mime-type":183,"filesize":435,"url":436},"Default-Updater-1-1024x683.png",11433,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FDefault-Updater-1-1024x683.png",{"file":438,"width":63,"height":63,"mime-type":183,"filesize":439,"url":440},"Default-Updater-1-150x150.png",1553,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FDefault-Updater-1-150x150.png",{"file":442,"width":68,"height":361,"mime-type":183,"filesize":443,"url":444},"Default-Updater-1-768x512.png",6120,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FDefault-Updater-1-768x512.png",{"file":446,"width":86,"height":86,"mime-type":183,"filesize":447,"url":448},"Default-Updater-1-100x100.png",856,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FDefault-Updater-1-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":450},[],904,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FDefault-Updater-1.png",[104,103,273],{"self":455,"collection":460,"about":462,"author":464,"replies":466,"version-history":469,"predecessor-version":472,"acf:post":476,"wp:attachment":481,"wp:term":484,"curies":489},[456],{"href":457,"targetHints":458},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F768",{"allow":459},[111],[461],{"href":114},[463],{"href":117},[465],{"embeddable":120,"href":121},[467],{"embeddable":120,"href":468},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=768",[470],{"count":231,"href":471},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F768\u002Frevisions",[473],{"id":474,"href":475},1197,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F768\u002Frevisions\u002F1197",[477,479,480],{"embeddable":120,"href":478},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F9",{"embeddable":120,"href":137},{"embeddable":120,"href":135},[482],{"href":483},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=768",[485,487],{"taxonomy":143,"embeddable":120,"href":486},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=768",{"taxonomy":146,"embeddable":120,"href":488},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=768",[490],{"name":150,"href":151,"templated":120},{"id":492,"date":493,"date_gmt":494,"guid":495,"modified":497,"modified_gmt":498,"slug":499,"status":14,"type":15,"link":500,"title":501,"content":503,"excerpt":505,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":507,"categories":508,"application":509,"class_list":510,"acf":512,"_links":546},766,"2023-08-22T17:21:31","2023-08-22T21:21:31",{"rendered":496},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=766","2026-05-24T23:18:19","2026-05-25T03:18:19","4-port-isolation-transceiver","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2023\u002F08\u002F22\u002F4-port-isolation-transceiver\u002F",{"rendered":502},"4 Port Isolation Transceiver",{"rendered":504,"protected":21},"\u003Ch1>Part# M-SS3005\u003C\u002Fh1>\n\u003Cp>We’ve overhauled the 3 port Transceiver to a 4-port transceiver. 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The now legacy 3 port transceiver and the evolved 4 port transceiver will continue to offer: All Transceiver Basic Features Provides the ‘topside’ interface to the Synapse, SeaSPY or SeaQuest magnetometer system. Connects to a PC via a RS232 serial or USB port. 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Iron Wreck of Eagle Island",{"rendered":603,"protected":21},"\u003Cp>In December 2021, the Chagos Remote Ocean Voyager Expedition\u003Cbr \u002F>\n(C-Rove) discovered a shipwreck off the west coast of Eagle Island.\u003C\u002Fp>\n\u003Cp>The Chagos Remote Ocean Voyager Expedition (C-Rove), organized by the OceanGate Foundation, aimed to investigate the theory that ancient Greek and Roman navigators traded across the central Indian Ocean via the southern monsoon route.\u003C\u002Fp>\n\u003Cp>The search for evidence in shipwrecks targeted islands along the route, particularly the Chagos Archipelago in the British Indian Ocean Territory.\u003C\u002Fp>\n\u003Cp>The large search area necessitated an unconventional approach—using rat populations as indicators of human seafaring. Genetic analysis techniques allowed the determination of the rats’ geographic origin and estimated arrival time.\u003C\u002Fp>\n\u003Cp>In December 2021, the C-Rove team embarked on the expedition to collect rat tail samples from the archipelago’s major atolls (excluding Diego Garcia), aboard the 18-metre sailing yacht Jocara. Owned by the Potter family from Trondheim, Norway, Jocara proved to be an excellent representation of oceanography’s environmentally-friendly shift towards wind-powered seafaring.\u003C\u002Fp>\n\u003Cdiv>\n\u003Cp>Early results from analyzing the Chagos rats at Fordham University’s Munshi-South Lab are promising.Furthermore, an unexpected discovery made during the expedition deserves mention. In addition to rat sampling, the expedition also aimed to assess Jocara’s potential as a platform for remote maritime archaeological surveys.\u003C\u002Fp>\n\u003Cp>To detect possible ancient shipwrecks, we conducted a magnetic survey using a Marine Magnetics \u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fproducts\u002Fmarine-magnetometers\u002Fexplorer\u002F\">Explorer\u003C\u002Fa> magnetometer attached to a plastic kayak towed by Jocara’s dinghy. This compact, low-impact setup performed admirably, locating a shipwreck off Eagle Island in its initial test.\u003C\u002Fp>\n\u003Cp>Credit must be given to Catholic Friar Roger Dussercle, whose memoirs hinted at the possibility of shipwreck artifacts near Eagle Island. His records, along with a shipwreck list from Nigel Wenban-Smith’s 2016 book, “Chagos: A History,” informed our search locations. The magnetometer detected wreckage seemingly from a large turn-of-the-century iron-hulled vessel covering an area of 50-60 square meters.\u003C\u002Fp>\n\u003C\u002Fdiv>\n",{"rendered":605,"protected":21},"\u003Cp>In December 2021, the Chagos Remote Ocean Voyager Expedition (C-Rove) discovered a shipwreck off the west coast of Eagle Island. The Chagos Remote Ocean Voyager Expedition (C-Rove), organized by the OceanGate Foundation, aimed to investigate the theory that ancient Greek and Roman navigators traded across the central Indian Ocean via the southern monsoon route. The […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],11,[610,611],17,18,[613,15,36,37,38,39,614,615,616],"post-755","category-in-action","application-archeology","application-environment-survey",{"external_link":28,"hero_media":618,"credits":656,"related_products":657},{"width":619,"height":620,"file":621,"filesize":622,"sizes":623,"image_meta":652,"id":654,"url":655},1778,1276,"2023\u002F05\u002FIronWreckChicagoNews-Web.png",1082032,{"medium":624,"large":629,"thumbnail":634,"medium_large":638,"1536x1536":643,"chip":648},{"file":625,"width":50,"height":626,"mime-type":183,"filesize":627,"url":628},"IronWreckChicagoNews-Web-300x215.png",215,55243,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web-300x215.png",{"file":630,"width":57,"height":631,"mime-type":183,"filesize":632,"url":633},"IronWreckChicagoNews-Web-1024x735.png",735,494234,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web-1024x735.png",{"file":635,"width":63,"height":63,"mime-type":183,"filesize":636,"url":637},"IronWreckChicagoNews-Web-150x150.png",21598,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web-150x150.png",{"file":639,"width":68,"height":640,"mime-type":183,"filesize":641,"url":642},"IronWreckChicagoNews-Web-768x551.png",551,295791,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web-768x551.png",{"file":644,"width":74,"height":645,"mime-type":183,"filesize":646,"url":647},"IronWreckChicagoNews-Web-1536x1102.png",1102,1029775,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web-1536x1102.png",{"file":649,"width":86,"height":86,"mime-type":183,"filesize":650,"url":651},"IronWreckChicagoNews-Web-100x100.png",10391,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":653,"alt":28},[],1192,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2023\u002F05\u002FIronWreckChicagoNews-Web.png","\u003Cp>Adapted from Chagos Remote Ocean Voyager Expedition (C-Rove) field report, 2021–2022.\u003Cbr data-start=\"1130\" data-end=\"1133\" \u002F>Shared by Dr. Bridget Buxton (University of Rhode Island), with permission from the OceanGate Foundation.\u003C\u002Fp>\n",[658],120,{"self":660,"collection":665,"about":667,"author":669,"replies":671,"version-history":674,"predecessor-version":677,"acf:post":681,"wp:attachment":684,"wp:term":687,"curies":692},[661],{"href":662,"targetHints":663},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F755",{"allow":664},[111],[666],{"href":114},[668],{"href":117},[670],{"embeddable":120,"href":121},[672],{"embeddable":120,"href":673},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=755",[675],{"count":231,"href":676},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F755\u002Frevisions",[678],{"id":679,"href":680},1194,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F755\u002Frevisions\u002F1194",[682],{"embeddable":120,"href":683},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F120",[685],{"href":686},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=755",[688,690],{"taxonomy":143,"embeddable":120,"href":689},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=755",{"taxonomy":146,"embeddable":120,"href":691},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=755",[693],{"name":150,"href":151,"templated":120},{"id":695,"date":696,"date_gmt":697,"guid":698,"modified":700,"modified_gmt":701,"slug":702,"status":14,"type":15,"link":703,"title":704,"content":706,"excerpt":708,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":710,"categories":711,"application":712,"class_list":714,"acf":717,"_links":730},312,"2023-05-25T16:44:55","2023-05-25T20:44:55",{"rendered":699},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=312","2026-04-13T12:46:53","2026-04-13T16:46:53","sea-trial-report-synapse-4-magnetometer-array","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2023\u002F05\u002F25\u002Fsea-trial-report-synapse-4-magnetometer-array\u002F",{"rendered":705},"Sea Trial Report: Synapse 4-Magnetometer Array",{"rendered":707,"protected":21},"\u003Ch2>System Overview\u003C\u002Fh2>\n\u003Cp>Synapse is a new ultra-light, high-sensitivity marine magnetometer array system based on low-power rubidium optically-pumped scalar sensors. The array is scalable from 1 to 30 units, with automatic time synchronization handled by the networking hardware in each towfish.\u003C\u002Fp>\n\u003Cp>The rubidium magnetometer sensor can sample at rates up to 20 Hz while maintaining low noise, excellent resolution and sensitivity, and having only one dead zone: equatorial. In contrast to traditional optically pumped magnetometers, which have both equatorial and polar dead zones.\u003C\u002Fp>\n\u003Cp>Synapse towfish can be used as standalone magnetometers or combined into an array and feature flexible configurations that may include any combination of the following sensors: scalar magnetometer, pressure sensor, altimeter and tilt\u002FIMU. Standard configurations include a 1000m pressure housing, a network status LED and a leak detector. Telemetry and power are supplied to all nodes via the same 2-conductor link from the vessel. The Synapse evaluation system used for this demonstration included:\u003C\u002Fp>\n\u003Cul>\n\u003Cli>A 4-magnetometer streamlined rigid and lightweight aluminum frame.\u003C\u002Fli>\n\u003Cli>The frame had an overall width of 3m and 1m magnetometer sensor spacing.\u003C\u002Fli>\n\u003Cli>An additional attitude node positioned in the center of the frame contained a pressure sensor, an altimeter (SBES) and a 3-axis gyrocompensated IMU for frame tilt monitoring.\u003C\u002Fli>\n\u003Cli>An 80m soft tow cable for towing the array, connected via a 6.3m Y-split adapter cable.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Ch2>Summary\u003C\u002Fh2>\n\u003Cp>The Synapse Magnetometer Array System features small size, light weight, low power consumption, high sensitivity, and fast sampling for high data resolution.\u003C\u002Fp>\n\u003Cp>This sea trial confirmed all of these features, and in addition highlighted fast and easy setup.\u003C\u002Fp>\n\u003Cul>\n\u003Cli>Initial assembly of the four-sensor gradiometer and frame required minimal time (approximately 45 minutes) and allowed early transit to the survey area, maximizing data collection time.\u003C\u002Fli>\n\u003Cli>Finally, the array was easily deployable over the vessel side by two deckhands, meaning it was lightweight enough not to require a crane or other lifting device.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>Inspection of the sensor profiles confirmed that the rubidium optically pumped magnetometer sensors exhibit low noise and show excellent time synchronization between all sensors in the array. Data processing required only the simple steps of diurnal correction and basic bulk shifting.\u003C\u002Fp>\n\u003Cul>\n\u003Cli>No frequency-based filtering or advanced data manipulation was necessary to produce a coherent total field map.\u003C\u002Fli>\n\u003Cli>Two of the three notable anomalies on the magnetic maps matched the location of notable features on the MBES bathymetry data.\u003C\u002Fli>\n\u003Cli>The third magnetic anomaly had no corresponding surface expression in the bathymetry data and most likely originated from a buried source.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>Despite the relatively small 3m width of the array frame, it’s clear from both data profiles and the interpolated maps that having four sensors was beneficial to capturing additional data over the encountered anomalies, helping enhance the resolution of the final data and adding valuable directional definition in each case, as compared to a single sensor towfish.\u003C\u002Fp>\n\u003Cp>The main challenges encountered during the sea trial can be attributed to the control and behaviour of the prototype frame and its ability to handle the current. Ongoing work will involve design improvements to stabilize the frame, to reduce roll and pitch angles to reasonable levels, less than 10 degrees.\u003C\u002Fp>\n\u003Cp>Overall, the sea trial successfully demonstrated the capabilities of the Synapse Array and the benefits of operating multiple simultaneous total-field magnetic sensors when detecting near-surface targets and hazards.\u003C\u002Fp>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002F202306-MM_Report_SynapseTrial.pdf\">Download the Full Report\u003C\u002Fa>\u003C\u002Fdiv>\n",{"rendered":709,"protected":21},"\u003Cp>The Synapse Magnetometer Array System features small size, light weight, low power consumption, high sensitivity, and fast sampling for high data resolution.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[713],19,[715,15,36,37,38,39,614,716],"post-312","application-geophysical-exploration",{"external_link":28,"hero_media":718,"credits":728,"related_products":729},{"bitrate":719,"filesize":720,"mime_type":272,"length":721,"length_formatted":722,"width":723,"height":724,"fileformat":275,"dataformat":725,"id":726,"url":727},3704364,926091,2,"0:02",1280,960,"V_VP9",377,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F02\u002Fsynapsehgrad-loop2s.webm","\u003Cp data-start=\"210\" data-end=\"353\">Originally published in \u003Cem data-start=\"234\" data-end=\"308\">Sea Trial Report: Synapse 4-Magnetometer Array, Revision 1.1 (May 2023).\u003Cbr \u002F>\n\u003C\u002Fem>Written by Marine Magnetics Corporation.\u003C\u002Fp>\n",[104,103],{"self":731,"collection":736,"about":738,"author":740,"replies":742,"version-history":745,"predecessor-version":748,"acf:post":752,"wp:attachment":755,"wp:term":758,"curies":763},[732],{"href":733,"targetHints":734},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F312",{"allow":735},[111],[737],{"href":114},[739],{"href":117},[741],{"embeddable":120,"href":121},[743],{"embeddable":120,"href":744},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=312",[746],{"count":332,"href":747},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F312\u002Frevisions",[749],{"id":750,"href":751},998,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F312\u002Frevisions\u002F998",[753,754],{"embeddable":120,"href":137},{"embeddable":120,"href":135},[756],{"href":757},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=312",[759,761],{"taxonomy":143,"embeddable":120,"href":760},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=312",{"taxonomy":146,"embeddable":120,"href":762},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=312",[764],{"name":150,"href":151,"templated":120},{"id":766,"date":767,"date_gmt":768,"guid":769,"modified":771,"modified_gmt":772,"slug":773,"status":14,"type":15,"link":774,"title":775,"content":777,"excerpt":779,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":781,"categories":782,"application":783,"class_list":784,"acf":786,"_links":819},921,"2022-07-06T10:01:26","2022-07-06T14:01:26",{"rendered":770},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=921","2026-01-26T11:58:28","2026-01-26T16:58:28","maritime-heritage-in-americas-inland-seas","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2022\u002F07\u002F06\u002Fmaritime-heritage-in-americas-inland-seas\u002F",{"rendered":776},"Maritime Heritage in America’s Inland Seas",{"rendered":778,"protected":21},"\u003Ch1>A Multi-Tiered Autonomous Vehicle-Based Survey of Two Proposed Great Lakes National Marine Sanctuaries\u003C\u002Fh1>\n\u003Ch3>\u003Cstrong>From July 28 to August 20, 2021, an interdisciplinary team of researchers led by NOAA’s Office of National Marine Sanctuaries searched for maritime heritage resources in Lakes Michigan and Ontario using a suite of crewed and uncrewed (autonomous) systems.\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002F21greatlakes-final-report.pdf\">Download original file\u003C\u002Fa>\u003C\u002Fdiv>\n\u003Cp>The Great Lakes provide a natural water highway extending into the heart of North America and have long been critical to the economic and social development of the United States. Six thousand historic shipwrecks are estimated to be submerged across the five Great Lakes, serving as tangible reminders of the hard work involved in our nation’s building. As such, the \u003Ca href=\"https:\u002F\u002Fsanctuaries.noaa.gov\u002Fwisconsin\u002F\" target=\"_blank\" rel=\"noopener\">Wisconsin Shipwreck Coast National Marine Sanctuary\u003C\u002Fa> in Lake Michigan was designated in 2021, and a \u003Ca href=\"https:\u002F\u002Fsanctuaries.noaa.gov\u002Flake-ontario\u002F\" target=\"_blank\" rel=\"noopener\">proposed Lake Ontario National Marine Sanctuary\u003C\u002Fa> is under consideration.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_2407\" style=\"width: 632px\" class=\"wp-caption aligncenter\">\u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmap-hires-7-1.jpg\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2407\" class=\"size-full wp-image-2407\" src=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmap-hires-7-1.jpg\" alt=\"\" width=\"622\" height=\"478\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-2407\" class=\"wp-caption-text\">Map showing the Wisconsin Shipwreck Coast National Marine Sanctuary in Lake Michigan and the proposed Lake Ontario National Marine Sanctuary in Lake Ontario, which were surveyed during the Maritime Heritage in America’s Inland Seas expedition.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>Shipwrecks can be difficult to detect and reach, which makes it challenging to explore, identify, and evaluate them. To overcome these challenges and survey and characterize the diverse underwater and coastal environments of Lakes Michigan and Ontario, the team of federal, state, academic, commercial, and nonprofit partners devised and employed a novel approach using three coordinated autonomous mapping platforms outfitted with multibeam and side-scan sonars, magnetometers, and cameras. These platforms included an uncrewed aerial vehicle for mapping above the surf zone, autonomous surface vehicles for shallow-water mapping, and an autonomous underwater vehicle for deep-water mapping. Scientific diving\u002Fsnorkeling operations were also conducted to investigate anomalies in the data, where appropriate.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_2400\" style=\"width: 631px\" class=\"wp-caption aligncenter\">\u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fiver3-hires.jpg\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2400\" class=\"size-full wp-image-2400\" src=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fiver3-hires.jpg\" alt=\"\" width=\"621\" height=\"430\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-2400\" class=\"wp-caption-text\">The University of Delaware Iver3 autonomous underwater vehicle used during the Maritime Heritage in America’s Inland Seas expedition.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>During their field operations, the team surveyed known shipwreck sites, refining their locations and descriptions, as well as new sites of interest and potential historic significance on the lake beds. Among the known shipwrecks, the historic barge Onondaga and steamer Ellsworth are in good condition with few anthropogenic impacts. New discoveries include two potential historic resources, one in each of the lakes. Additional research is recommended to support evaluation of the proposed Lake Ontario National Marine Sanctuary, the eligibility of known and new resources for the National Register of Historic Places, and more.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_2408\" style=\"width: 593px\" class=\"wp-caption aligncenter\">\u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fonondaga-hires.jpg\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2408\" class=\"size-full wp-image-2408\" src=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fonondaga-hires.jpg\" alt=\"\" width=\"583\" height=\"516\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-2408\" class=\"wp-caption-text\">The historic vessel Onondaga as seen in side-scan sonar data collected by an autonomous underwater vehicle Maritime Heritage in America’s Inland Seas expedition.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv class=\"log-image media-wrapper\">\n\u003Cdiv id=\"attachment_2409\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmast-500.jpg\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2409\" class=\"size-full wp-image-2409\" src=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmast-500.jpg\" alt=\"\" width=\"500\" height=\"312\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-2409\" class=\"wp-caption-text\">The standing mast on Onondaga, showing a good degree of structural integrity, imaged by an autonomous underwater vehicle during the Maritime Heritage in America’s Inland Seas expedition.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>To further this research, the expedition team will archive and make their data publicly available through the \u003Ca title=\"NOAA Ocean Exploration Data Atlas\" href=\"https:\u002F\u002Fwww.ncei.noaa.gov\u002Fmaps\u002Focean-exploration-data-atlas\u002F\" target=\"_blank\" rel=\"noopener\">NOAA Ocean Exploration Data Atlas\u003C\u002Fa>. They hope that their exploratory efforts will catalyze future ground-truthing to improve our knowledge about the history of U.S. inland seas and support investigations of other maritime heritage resources.\u003C\u002Fp>\n\u003Cp>\u003Cem>Originally published by \u003Ca href=\"https:\u002F\u002Foceanexplorer.noaa.gov\u002Fexpedition-feature\u002F21greatlakes-features-summary\u002F\">NOAA Ocean Exploration\u003C\u002Fa> – July 6, 2022\u003C\u002Fem>\u003C\u002Fp>\n\u003C\u002Fdiv>\n",{"rendered":780,"protected":21},"\u003Cp>A Multi-Tiered Autonomous Vehicle-Based Survey of Two Proposed Great Lakes National Marine Sanctuaries\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[610],[785,15,36,37,38,39,335,615],"post-921",{"external_link":787,"hero_media":788,"credits":816,"related_products":817},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002F21greatlakes-final-report.pdf",{"width":789,"height":790,"file":791,"filesize":792,"sizes":793,"image_meta":807,"id":814,"url":815},622,478,"2026\u002F01\u002Fmap-hires-7.jpg",283490,{"medium":794,"thumbnail":799,"chip":803},{"file":795,"width":50,"height":796,"mime-type":52,"filesize":797,"url":798},"map-hires-7-300x231.jpg",231,34384,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmap-hires-7-300x231.jpg",{"file":800,"width":63,"height":63,"mime-type":52,"filesize":801,"url":802},"map-hires-7-150x150.jpg",20530,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmap-hires-7-150x150.jpg",{"file":804,"width":86,"height":86,"mime-type":52,"filesize":805,"url":806},"map-hires-7-100x100.jpg",16844,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmap-hires-7-100x100.jpg",{"aperture":210,"credit":808,"camera":28,"caption":809,"created_timestamp":810,"copyright":811,"focal_length":210,"iso":210,"shutter_speed":210,"title":812,"orientation":96,"keywords":813},"NOAA","Map showing the Wisconsin Shipwreck Coast National Marine Sanctuary in Lake Michigan and the proposed Lake Ontario National Marine Sanctuary in Lake Ontario, which were surveyed during the Maritime Heritage in America’s Inland Seas expedition.","1561474538","Image courtesy of NOAA .","Maritime Heritage in America’s Inland Seas: A Multi-Tiered Aut",[],922,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2026\u002F01\u002Fmap-hires-7.jpg","\u003Cp>NOAA Ocean Exploration. (2025). \u003Cem>2021 Great Lakes Expedition: Final Report\u003C\u002Fem>. National Oceanic and Atmospheric Administration.\u003C\u002Fp>\n",[818,658],117,{"self":820,"collection":825,"about":827,"author":829,"replies":831,"version-history":834,"predecessor-version":837,"acf:post":841,"wp:attachment":845,"wp:term":848,"curies":853},[821],{"href":822,"targetHints":823},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F921",{"allow":824},[111],[826],{"href":114},[828],{"href":117},[830],{"embeddable":120,"href":121},[832],{"embeddable":120,"href":833},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=921",[835],{"count":297,"href":836},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F921\u002Frevisions",[838],{"id":839,"href":840},929,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F921\u002Frevisions\u002F929",[842,843],{"embeddable":120,"href":683},{"embeddable":120,"href":844},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F117",[846],{"href":847},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=921",[849,851],{"taxonomy":143,"embeddable":120,"href":850},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=921",{"taxonomy":146,"embeddable":120,"href":852},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=921",[854],{"name":150,"href":151,"templated":120},{"id":856,"date":857,"date_gmt":858,"guid":859,"modified":861,"modified_gmt":862,"slug":863,"status":14,"type":15,"link":864,"title":865,"content":867,"excerpt":869,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":871,"categories":872,"application":873,"class_list":875,"acf":878,"_links":910},761,"2018-12-01T17:14:55","2018-12-01T22:14:55",{"rendered":860},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=761","2026-01-26T13:15:23","2026-01-26T18:15:23","teledyne-gavia-integrates-marine-magnetics-explorer-magnetometer-with-the-gavia-auv","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2018\u002F12\u002F01\u002Fteledyne-gavia-integrates-marine-magnetics-explorer-magnetometer-with-the-gavia-auv\u002F",{"rendered":866},"Teledyne Gavia integrates Marine Magnetics’ Explorer Magnetometer with the Gavia AUV\u002FASV",{"rendered":868,"protected":21},"\u003Csection class=\"content\">\n\u003Ch3>​Reykjavik, Iceland, April, 2018: Teledyne Gavia, manufacturer of the Gavia Autonomous Underwater Vehicle (AUV\u002FASV), announces the integration of Marine Magnetics’ Explorer AUV\u002FASV magnetometer.\u003C\u002Fh3>\n\u003Cp>Underwater survey work is frequently carried out using autonomous underwater vehicles (AUVs\u002FASVs). The benefits of using AUVs\u002FASVs are that they are programmed to carry out missions without intervention, can fly at consistent low altitudes to achieve high resolution measurements, and are not as sensitive to surface conditions as a tethered system.\u003C\u002Fp>\n\u003Cp>AUVs\u002FASVs can be equipped with a wide range of sensors, including side-scan sonar, multi-beam echo sounders, sub-bottom profilers and cameras. Magnetometer surveys are conducted routinely in mining and petroleum resource exploration, archaeological surveys, and for detecting and locating pipelines and other seabed or buried ferrometallic objects.\u003C\u002Fp>\n\u003Cp>Magnetometers have always been a particular challenge to mount on AUVs, because of their strong magnetic signatures and strict power budgets, until now. Towing the \u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fproducts\u002Fmarine-magnetometers\u002Fauv\u002F\">Explorer AUV\u002FASV\u003C\u002Fa> Magnetometer behind the AUV\u002FASV solves this challenge due it its small size, low drag and 2 watt power requirement.\u003C\u002Fp>\n\u003Cp>During the week of February 11th to February 17th, 2018, Teledyne Gavia and Marine Magnetics carried out a trial with the Gavia AUV\u002FASV towing the Explorer AUV\u002FASV Mag. This trial showed that the magnetometer can detect targets weighing as little as 1kg.\u003C\u002Fp>\n\u003C\u002Fsection>\n",{"rendered":870,"protected":21},"\u003Cp>A Gavia AUV equipped with a towed Explorer magnetometer detected targets as small as 1 kg.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[610,874,713],16,[876,15,36,37,38,39,614,615,877,716],"post-761","application-cable-pipeline",{"external_link":28,"hero_media":879,"credits":907,"related_products":908},{"width":340,"height":341,"file":880,"filesize":881,"sizes":882,"image_meta":903,"id":905,"url":906},"2025\u002F12\u002FUsingAUVS_2.png",1895588,{"medium":883,"large":887,"thumbnail":891,"medium_large":895,"chip":899},{"file":884,"width":50,"height":347,"mime-type":183,"filesize":885,"url":886},"UsingAUVS_2-300x200.png",123505,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FUsingAUVS_2-300x200.png",{"file":888,"width":57,"height":352,"mime-type":183,"filesize":889,"url":890},"UsingAUVS_2-1024x683.png",1195454,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FUsingAUVS_2-1024x683.png",{"file":892,"width":63,"height":63,"mime-type":183,"filesize":893,"url":894},"UsingAUVS_2-150x150.png",49152,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FUsingAUVS_2-150x150.png",{"file":896,"width":68,"height":361,"mime-type":183,"filesize":897,"url":898},"UsingAUVS_2-768x512.png",710504,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FUsingAUVS_2-768x512.png",{"file":900,"width":86,"height":86,"mime-type":183,"filesize":901,"url":902},"UsingAUVS_2-100x100.png",23057,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FUsingAUVS_2-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":904},[],838,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FUsingAUVS_2.png","\u003Cp>Adapted from a Teledyne Gavia press release, April 2018.\u003C\u002Fp>\n",[909],121,{"self":911,"collection":916,"about":918,"author":920,"replies":922,"version-history":925,"predecessor-version":929,"acf:post":933,"wp:attachment":936,"wp:term":939,"curies":944},[912],{"href":913,"targetHints":914},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F761",{"allow":915},[111],[917],{"href":114},[919],{"href":117},[921],{"embeddable":120,"href":121},[923],{"embeddable":120,"href":924},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=761",[926],{"count":927,"href":928},4,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F761\u002Frevisions",[930],{"id":931,"href":932},842,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F761\u002Frevisions\u002F842",[934],{"embeddable":120,"href":935},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F121",[937],{"href":938},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=761",[940,942],{"taxonomy":143,"embeddable":120,"href":941},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=761",{"taxonomy":146,"embeddable":120,"href":943},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=761",[945],{"name":150,"href":151,"templated":120},{"id":947,"date":948,"date_gmt":949,"guid":950,"modified":952,"modified_gmt":953,"slug":954,"status":14,"type":15,"link":955,"title":956,"content":958,"excerpt":960,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":962,"categories":963,"application":964,"class_list":965,"acf":967,"_links":998},739,"2016-08-03T16:39:11","2016-08-03T20:39:11",{"rendered":951},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=739","2026-05-24T23:19:24","2026-05-25T03:19:24","using-an-auv-asv-borne-magnetometer","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2016\u002F08\u002F03\u002Fusing-an-auv-asv-borne-magnetometer\u002F",{"rendered":957},"Using An AUV\u002FASV-Borne Magnetometer",{"rendered":959,"protected":21},"\u003Csection class=\"content\">\n\u003Cdiv id=\"attachment_1074\" class=\"wp-caption aligncenter\">\n\u003Cdiv id=\"attachment_1074\" style=\"width: 729px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.01.32-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1074\" class=\"wp-image-1074 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.01.32-PM.png\" alt=\"Neither Explorer nor the Iver2 require a large vessel, or a lot of deck space.\" width=\"719\" height=\"288\" aria-describedby=\"caption-attachment-1074\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1074\" class=\"wp-caption-text\">Neither Explorer nor the Iver2 require a large vessel, or a lot of deck space.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003C\u002Fdiv>\n\u003Cp>The conditions were completely unsuitable for boattowed survey, but the Iver2 had no problem.\u003C\u002Fp>\n\u003Cblockquote>\u003Cp>AUVs\u002FASVs are powerful platforms for marine survey, wielding an arsenal of sensors and giving the ability to get closer to investigated targets reliably, consistently and inexpensively.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>Magnetometers have always been a particular challenge to mount on AUVs\u002FASV because of their strong magnetic signatures.\u003C\u002Fp>\n\u003Cp>AUVs\u002FASV must use electric motors for all their actuators, and these in turn create strong magnetic fields when they operate, interfering with the magnetometer sensor.\u003C\u002Fp>\n\u003Cp>Further, AUVs\u002FASV have strict power budgets. Small increases in power consumption or hydrodynamic drag will shorten their runtime.\u003C\u002Fp>\n\u003Cp>To solve the problem, an AUVs\u002FASV was needed whose magnetism was mild at best, and a magnetometer was needed that was small, and low-powered. Iver2 is a handdeployable vehicle designed for quick deployment in inshore (<100m water depth) conditions.\u003C\u002Fp>\n\u003Cp>Explorer is the smallest, lightest marine total-field magnetometer ever developed – using high accuracy Overhauser technology for high sensitivity, low noise and extremely low power consumption. Together, the two created the perfect combination.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1076\" class=\"wp-caption aligncenter\">\n\u003Cdiv id=\"attachment_1076\" style=\"width: 725px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.03.17-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1076\" class=\"wp-image-1076 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.03.17-PM.png\" alt=\"The total-fi eld magnetic dataset acquired by the Iver2-Explorer, showing the survey track, which is extremely straight and precise. If AUV-induced error were present, one would expect to see ‘striping’ along the direction of the survey lines. Instead, the background fi eld is very smooth and gradual, showcasing the accuracy of the data. The two linear anomalies are charted steel pipelines.\" width=\"715\" height=\"676\" aria-describedby=\"caption-attachment-1076\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1076\" class=\"wp-caption-text\">The total-field magnetic dataset acquired by the Iver2-Explorer, showing the survey track, which is extremely straight and precise. If AUV\u002FASV-induced error were present, one would expect to see ‘striping’ along the direction of the survey lines. Instead, the background field is very smooth and gradual, showcasing the accuracy of the data. The two linear anomalies are charted steel pipelines.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp id=\"caption-attachment-1076\" class=\"wp-caption-text\">The total-field magnetic dataset acquired by the Iver2-Explorer, showing the survey track, which is extremely straight and precise. If AUV\u002FASV-induced error were present, one would expect to see ‘striping’ along the direction of the survey lines. Instead, the background field is very smooth and gradual, showcasing the accuracy of the data. The two linear anomalies are charted steel pipelines.\u003C\u002Fp>\n\u003C\u002Fdiv>\n\u003Cdiv id=\"attachment_1075\" class=\"wp-caption aligncenter\">\n\u003Cdiv id=\"attachment_1075\" style=\"width: 726px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.03.29-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1075\" class=\"wp-image-1075 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.03.29-PM.png\" alt=\"The total-fi eld magnetic dataset acquired by the Iver2-Explorer, showing the survey track, which is extremely straight and precise. If AUV-induced error were present, one would expect to see ‘striping’ along the direction of the survey lines. Instead, the background fi eld is very smooth and gradual, showcasing the accuracy of the data. The two linear anomalies are charted steel pipelines.\" width=\"716\" height=\"679\" aria-describedby=\"caption-attachment-1075\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1075\" class=\"wp-caption-text\">Explorer magnetometer data overlaid onto a mosaic of the side scan data, all collected by the Iver2 at the same time. The two data types are extremely complimentary, allowing powerful analysis of many geophysical variables at the same time. This image shows a small boat anchor detected by both the mag and the side scan sonar. Some small mag anomalies are not visible in the side scan record, indicating buried objects.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003Cblockquote>\u003Cp>Iver2 was designed with the capability to tow a small payload, allowing the Explorer sensor to be kept outside the AUV\u002FASV housing.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>Still, the amount of tow cable was practically limited to a small distance.\u003C\u002Fp>\n\u003Cp>After intensive lab testing and engineering at OceanServer’s and Marine Magnetics’ facilities, the next step was a true field test: an actual survey over a site with known magnetic anomalies, and a smooth regional background ambient magnetic field.\u003C\u002Fp>\n\u003Cp>The test site was on Lake Ontario, and it was conducted close to the end of the 2012 season, when weather conditions were rarely calm and nice.\u003C\u002Fp>\n\u003Cp>Most of the survey was conducted at night, and in stormy conditions. Waves increased from 1m to 2m over the course of the project. Rain and thunderstorms began around the midpoint.\u003C\u002Fp>\n\u003Cblockquote>\u003Cp>The conditions were completely unsuitable for boattowed survey, but the Iver2 had no problem.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>Iver2 can be programmed to track the sea floor, or to survey at a fixed depth. Since the bathymetry of the area was not well known, and sharp inclines may have existed, Iver2 was programmed for a constant water depth of 3m. Survey speed was set to 2.5kts, which is nominal for the AUV\u002FASV.\u003C\u002Fp>\n\u003Cp>Slower speeds save power, and increase endurance. A side benefit of slower speed is higher spatial resolution for the magnetic data. Explorer was set to sample at 2Hz.\u003C\u002Fp>\n\u003Cp>Line spacing was set to 10m—a distance that would be a challenge to maintain reliably for a human boat operator, even in calm conditions, but Iver2 maintained it perfectly in a storm.\u003C\u002Fp>\n\u003Cp>A huge benefit of the system is that the Iver2 can maintain very tight line spacings, producing data with very high spatial resolution.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1077\" class=\"wp-caption aligncenter\">\n\u003Cdiv id=\"attachment_1077\" style=\"width: 538px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.09.22-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1077\" class=\"wp-image-1077 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.09.22-PM.png\" alt=\"Explorer is neutrally buoyant and tows directly behind the Iver2 with very little drag\" width=\"528\" height=\"350\" aria-describedby=\"caption-attachment-1077\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1077\" class=\"wp-caption-text\">Explorer is neutrally buoyant and tows directly behind the Iver2 with very little drag\u003C\u002Fp>\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003Cp>The entire survey required six hours to complete, totaling a little over 18 line-km. The magnetometer data was downloaded wirelessly directly from the Iver2, and processed. Two corrections were applied: the magnetometer coordinates were adjusted for the 5m tow cable length, and correction for diurnal variation was applied using data from the Ottawa magnetic observatory. The smoothness of the regional background field shows the extremely low error level in the data. Had there been\u003C\u002Fp>\n\u003Cp>Two corrections were applied: the magnetometer coordinates were adjusted for the 5m tow cable length, and correction for diurnal variation was applied using data from the Ottawa magnetic observatory. The smoothness of the regional background field shows the extremely low error level in the data. Had there been\u003C\u002Fp>\n\u003Cp>The smoothness of the regional background field shows the extremely low error level in the data. Had there been\u003C\u002Fp>\n\u003Cp>Had there been AUV\u002FASV-induced error, horizontal striping would be visible in the background field—no such striping is present.\u003C\u002Fp>\n\u003Cp>The strong pipeline anomalies in the center of the block are positioned accurately exactly where expected and shown on marine charts. Small point-source anomalies are visible throughout the block.\u003C\u002Fp>\n\u003Cp>The Iver2 also carried a Klein 3900 500kHz side scan sonar, which operated continuously during the survey. Collecting both side scan and magnetometer datasets with a single platform is a major benefit.\u003C\u002Fp>\n\u003Cp>The side scan mosaic is shown above, superimposed on the magnetic field plot. The two data forms provide complimentary information on detected targets. Some magnetic anomalies do not appear on the side scan mosaic, indicating they are buried. Others are clearly shown, such as the small anchor in the callout.\u003C\u002Fp>\n\u003Cblockquote>\u003Cp>The Iver2-Explorer combination represents a powerful, high accuracy survey tool.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>Precise positioning, high resolution coverage, excellent data quality, the ability to survey in harsh conditions, and with low operating costs make it an attractive tool for a magnetic surveyor’s toolkit.\u003C\u002Fp>\n\u003Cp>Explorer is available now in an Iver2-compatible configuration from Marine Magnetics. It simply plugs into any suitably equipped Iver2 vehicle, and is ready to survey.\u003C\u002Fp>\n\u003Ch5>The side scan sonar dataset was processed and mosaicked with Hypack. Thank you to Hypack for very generously providing Marine Magnetics with the software.\u003C\u002Fh5>\n\u003C\u002Fsection>\n",{"rendered":961,"protected":21},"\u003Cp>The Iver2–Explorer duo delivered crisp, interference-free magnetic data in stormy conditions that would shut down any boat-towed survey.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[611,713],[966,15,36,37,38,39,614,616,716],"post-739",{"external_link":28,"hero_media":968,"credits":996,"related_products":997},{"width":340,"height":341,"file":969,"filesize":970,"sizes":971,"image_meta":992,"id":994,"url":995},"2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1.png",1569214,{"medium":972,"large":976,"thumbnail":980,"medium_large":984,"chip":988},{"file":973,"width":50,"height":347,"mime-type":183,"filesize":974,"url":975},"Screenshot-2025-12-01-at-5.29.47-PM-1-1-300x200.png",110753,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1-300x200.png",{"file":977,"width":57,"height":352,"mime-type":183,"filesize":978,"url":979},"Screenshot-2025-12-01-at-5.29.47-PM-1-1-1024x683.png",1006522,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1-1024x683.png",{"file":981,"width":63,"height":63,"mime-type":183,"filesize":982,"url":983},"Screenshot-2025-12-01-at-5.29.47-PM-1-1-150x150.png",44152,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1-150x150.png",{"file":985,"width":68,"height":361,"mime-type":183,"filesize":986,"url":987},"Screenshot-2025-12-01-at-5.29.47-PM-1-1-768x512.png",601900,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1-768x512.png",{"file":989,"width":86,"height":86,"mime-type":183,"filesize":990,"url":991},"Screenshot-2025-12-01-at-5.29.47-PM-1-1-100x100.png",21949,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":993},[],852,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreenshot-2025-12-01-at-5.29.47-PM-1-1.png","\u003Cp data-start=\"56\" data-end=\"208\">Prepared by Marine Magnetics in collaboration with OceanServer Technology Inc.\u003C\u002Fp>\n",[909],{"self":999,"collection":1004,"about":1006,"author":1008,"replies":1010,"version-history":1013,"predecessor-version":1016,"acf:post":1020,"wp:attachment":1022,"wp:term":1025,"curies":1030},[1000],{"href":1001,"targetHints":1002},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F739",{"allow":1003},[111],[1005],{"href":114},[1007],{"href":117},[1009],{"embeddable":120,"href":121},[1011],{"embeddable":120,"href":1012},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=739",[1014],{"count":874,"href":1015},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F739\u002Frevisions",[1017],{"id":1018,"href":1019},1198,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F739\u002Frevisions\u002F1198",[1021],{"embeddable":120,"href":935},[1023],{"href":1024},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=739",[1026,1028],{"taxonomy":143,"embeddable":120,"href":1027},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=739",{"taxonomy":146,"embeddable":120,"href":1029},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=739",[1031],{"name":150,"href":151,"templated":120},{"id":1033,"date":1034,"date_gmt":1035,"guid":1036,"modified":1038,"modified_gmt":1039,"slug":1040,"status":14,"type":15,"link":1041,"title":1042,"content":1044,"excerpt":1046,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1048,"categories":1049,"application":1050,"class_list":1051,"acf":1053,"_links":1084},50,"2016-08-03T15:01:40","2016-08-03T19:01:40",{"rendered":1037},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=50","2025-12-01T16:33:55","2025-12-01T21:33:55","auvs-tackle-the-problem-of-uxo","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2016\u002F08\u002F03\u002Fauvs-tackle-the-problem-of-uxo\u002F",{"rendered":1043},"AUVs Tackle The Problem Of UXO",{"rendered":1045,"protected":21},"\u003Ch1>Today’s AUVs provide a common-sense approach to the global issue of detecting and monitoring underwater unexploded ordnance\u003C\u002Fh1>\n\u003Cp>Unexploded ordnance (UXO), improperly deployed (or dumped) in the world’s oceans and lakes for the past 70-plus years, are becoming a critical concern for the safety of people and the long-term health of subsea habitats and fish stocks. Risks to humans can result from munitions washing up on beaches, or fishermen inadvertently capturing devices in their nets or trawls, and eventually from chemicals undetectably leaching into the environment as the steel casings on older munitions deteriorate. Any of these possibilities could eventually result in devastating human contact or environmental damage.\u003C\u002Fp>\n\u003Cp>While there has not been much of an appetite by governments to fund largescale clean-ups, technology demonstrations and limited real-world ‘remediation’ projects have been funded with an aim towards developing equipment and methodologies to identify, localise and neutralise the unexploded munitions. Remotely operated vehicles and autonomous underwater vehicles are two modern tools being used to assess seafloor debris, remove items of interest and perform long-term monitoring of these potentially dangerous sites.\u003C\u002Fp>\n\u003Cp>Today’s AUVs provide a common-sense approach to this global issue with a growing list of detection and localisation capabilities, including high-resolution sonar (sidescan\u002Finterferometric bathy), camera systems, a variety of environmental sensors and, most recently, small total-field magnetometers that can be towed through the survey area. Using an AUV platform, all sensor data can be collected and logged simultaneously, accurately geo-positioned and time-stamped and catalogued for postmission analysis or long-term research and monitoring – all done while keeping people out of direct contact with the potential hazards of UXO.\u003C\u002Fp>\n\u003Cp>One affordable and capable small AUV for near coastal work is the Iver AUV manufactured by OceanServer Technology in Massachusetts. When coupled with a small towed magnetometer, the Explorer by Marine Magnetics of Ontario, Canada, it provides an easily-deployable tool for detecting ferrous objects such as UXO, even if they have been covered over by sediment or marine growth and are therefore not easy to identify using traditional imaging sensors such as cameras or sonar exclusively.\u003C\u002Fp>\n\u003Cp>OceanServer and Marine Magnetics started collaborating in 2011 with a magnetic characterisation of the Iver2 system. Integration of magnetometers with AUV platforms has historically been a difficult problem because of the strong magnetic fields created by the autonomous underwater vehicle’s batteries, power subsystem components, electromagnetic motors and servos\u002Factuators. Additionally, the power consumption of a towed magnetometer and the induced hydrodynamic drag of any towed device were detrimental to the AUV’s mission duration, stability and navigational accuracy.\u003C\u002Fp>\n\u003Cp>The Explorer’s use of Overhauser technology to provide high-sensitivity in noisy environments, and its power draw of less than two watts in a very small neutrally-buoyant housing, made it possible to integrate the system with this small AUV. Some hardware and software modifications needed to be made on both the magnetometer side and AUV side, but the low inherent magnetism of the Iver2 allowed the modifications to be kept simple, and eventual field testing validated that it was possible to tow the magnetometer only a short distance (two metres) behind the AUV without affecting the fidelity of the Explorer magnetometer.\u003C\u002Fp>\n\u003Cp>The AUV-towed mag system is a significant step forward, allowing users to get a consistent data set on close horizontal survey line spacing and at a fixed distance from the seafloor, both significant challenges when towing anything from a surface vessel, especially in rough weather and when searching for small targets like UXO.\u003C\u002Fp>\n\u003Cp>By the second half of 2012, OceanServer formally launched the product, and in the past few years the Iver 2 and Iver 3 AUVs, equipped with towed Explorer magnetometers, have completed dozens of surveys. The magnetometer data has exceeded all expectations. The Iver’s great control of position, depth and altitude, coupled with Explorer’s accurate and highsensitivity sensor, produced total-field data of such high quality that it is comparable to larger boat-towed gradiometer data. Below are some survey results from recent field projects.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1091\" style=\"width: 844px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.57.14-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1091\" class=\"size-full wp-image-1091\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.57.14-PM.png\" alt=\"Figure 1. Colour mag maps processed with GeoSoft software – raw data, before UXO seeding, and after UXO seeding; each ‘X’ indicates an unexploded ordnance detection\" width=\"834\" height=\"657\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1091\" class=\"wp-caption-text\">Figure 1. Colour mag maps processed with GeoSoft software – raw data, before UXO seeding, and after UXO seeding; each ‘X’ indicates an unexploded ordnance detection.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>San Diego Bay\u003C\u002Fh2>\n\u003Cp>In the summer of 2014, the Iver2-Explorer integration was tested at a UXO trial for the Geneva International Centre for Humanitarian Demining, Switzerland, in San Diego Bay, USA. Two 250-metre x 120- metre surveys were conducted over the same area. One before seeding with simulated UXO targets, and the second after seeding. The smallest target was onekilogram of steel and sizes ranged from 60 millimetres to 160 millimetres.\u003C\u002Fp>\n\u003Cp>The total-field map (figure 1) shows significant geological background obscuring small near-surface targets and a small pipeline in the lower half of the block. Twenty-six near-surface targets were detected before seeding. Post-processing of the collected mag data confirmed that all ten UXO were reliably detected after seeding.\u003C\u002Fp>\n\u003Ch2>Baltic Sea\u003C\u002Fh2>\n\u003Cp>In the autumn of 2014, OceanServer delivered an AUV to the Institute of Oceanology of the Polish Academy of Sciences in Sopot, Poland. The AUV was equipped with high-resolution sidescan sonar, a towed Explorer magnetometer and a full suite of environmental sensors utilising a YSI, USA, 6600 sonde mounted in the AUV bow. The AUV purchase and subsequent research was funded by the MODUM project supported under the NATO Science for Peace and Security (SPS) programme. The stated purpose of MODUM is to move “towards the monitoring of dumped munitions threats in the Baltic Sea”. Some of the key goals of the project were to establish a costeffective, research-based monitoring network using underwater vehicles to enhance the understanding of dumped munitions in the Baltic Sea, which pose both environmental and human security threats. This combination of sensors enables the AUV to identify likely munitions and take geo-registered environmental readings in close proximity to the targets. The status of the munitions in the Baltic Sea area are of particular concern given the high ship traffic, impact on fish\u002Ffishing and the ongoing development of offshore energy – for instance, wind farms.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1087\" style=\"width: 591px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.49.03-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1087\" class=\"size-full wp-image-1087\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.49.03-PM.png\" alt=\"Figure 2. Example mosaic with target marked by red rectangle. Inset: Zoom to red rectangle\" width=\"581\" height=\"435\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1087\" class=\"wp-caption-text\">Figure 2. Example mosaic with target marked by red rectangle. Inset: Zoom to red rectangle\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>A series of missions, as recently as September 2015, were deployed in the area of the Gdansk Deep (Southern Baltic Sea) by a team of researchers from the Institute of Oceanology of the Polish Academy of Sciences. Available sonar frequencies from the Klein, USA, 3500 include 455kHz and 900kHz, however, during missions in the Gdansk Deep only the higher frequency was used to obtain photo-like images. The AUV performed 12 missions in the area of interest and 67 targets were detected (figure 2). The AUV was also equipped with a Marine Magnetics Explorer towed magnetometer to detect magnetic anomalies during the survey, which could be used in conjunction with simultaneously collected sonar data to plan subsequent surveys. After every mission, data analysis was performed to localise targets. Magnetometer data was correlated with sonar data, which aided in planning ROV missions (figure 3). In addition, after every mission performed by the Iver AUV highresolution sonar mosaics were prepared.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1088\" style=\"width: 445px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.51.05-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1088\" class=\"size-full wp-image-1088\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FScreen-Shot-2016-08-03-at-2.51.05-PM.png\" alt=\"Figure 3. ROV’s photo inspection of detected object\" width=\"435\" height=\"371\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1088\" class=\"wp-caption-text\">Figure 3. ROV’s photo inspection of detected object\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>The Future\u003C\u002Fh2>\n\u003Cp>OceanServer expects that small AUVs, coupled with improved sensors, navigation methods and survey techniques, will increasingly be deployed to address the global issue of detecting and monitoring dumped UXO.\u003C\u002Fp>\n\u003Ch2>Acknowledgements\u003C\u002Fh2>\n\u003Cp>The author would like to acknowledge the contribution of the following participants to the content of this article:\u003C\u002Fp>\n\u003Cul>\n\u003Cli>Miłosz Grabowski, MSc, PhD student, marine geologist, AUV operator\u003C\u002Fli>\n\u003Cli>The Marine Acoustics Laboratory and Marine Physics Department of the Institute of Oceanology of Polish Academy of Sciences, Powstanców Warszawy 55, Sopot, Poland\u003C\u002Fli>\n\u003Cli>and Doug Hrvoic, Marine Magnetics, 135 SPY Court, Markham, ON, L3R 5H6, Canada.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FIOS_0116_OceanServer_lo-res.pdf\">Download Original Article\u003C\u002Fa>\u003C\u002Fdiv>\n",{"rendered":1047,"protected":21},"\u003Cp>OceanServer expects that small AUVs, coupled with improved sensors, navigation methods and survey techniques, will increasingly be deployed to address the global issue of detecting and monitoring dumped UXO.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[611,713,332],[1052,15,36,37,38,39,614,616,716,336],"post-50",{"external_link":28,"hero_media":1054,"credits":1082,"related_products":1083},{"width":340,"height":341,"file":1055,"filesize":1056,"sizes":1057,"image_meta":1078,"id":1080,"url":1081},"2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO.png",1092494,{"medium":1058,"large":1062,"thumbnail":1066,"medium_large":1070,"chip":1074},{"file":1059,"width":50,"height":347,"mime-type":183,"filesize":1060,"url":1061},"AUVs-Tackle-The-Problem-Of-UXO-300x200.png",67512,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO-300x200.png",{"file":1063,"width":57,"height":352,"mime-type":183,"filesize":1064,"url":1065},"AUVs-Tackle-The-Problem-Of-UXO-1024x683.png",608318,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO-1024x683.png",{"file":1067,"width":63,"height":63,"mime-type":183,"filesize":1068,"url":1069},"AUVs-Tackle-The-Problem-Of-UXO-150x150.png",27420,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO-150x150.png",{"file":1071,"width":68,"height":361,"mime-type":183,"filesize":1072,"url":1073},"AUVs-Tackle-The-Problem-Of-UXO-768x512.png",365534,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO-768x512.png",{"file":1075,"width":86,"height":86,"mime-type":183,"filesize":1076,"url":1077},"AUVs-Tackle-The-Problem-Of-UXO-100x100.png",12838,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1079},[],674,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F08\u002FAUVs-Tackle-The-Problem-Of-UXO.png","\u003Cp>Originally published by \u003Ca href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FIOS_0116_OceanServer_lo-res.pdf\">OceanServer Technology, Inc.\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Written by Jim Kirk, Business Development Manager, OceanServer Technology, Massachusetts, USA.\u003C\u002Fp>\n",[909],{"self":1085,"collection":1090,"about":1092,"author":1094,"replies":1096,"version-history":1099,"predecessor-version":1102,"acf:post":1106,"wp:attachment":1108,"wp:term":1111,"curies":1116},[1086],{"href":1087,"targetHints":1088},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F50",{"allow":1089},[111],[1091],{"href":114},[1093],{"href":117},[1095],{"embeddable":120,"href":121},[1097],{"embeddable":120,"href":1098},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=50",[1100],{"count":713,"href":1101},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F50\u002Frevisions",[1103],{"id":1104,"href":1105},675,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F50\u002Frevisions\u002F675",[1107],{"embeddable":120,"href":935},[1109],{"href":1110},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=50",[1112,1114],{"taxonomy":143,"embeddable":120,"href":1113},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=50",{"taxonomy":146,"embeddable":120,"href":1115},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=50",[1117],{"name":150,"href":151,"templated":120},{"id":1119,"date":1120,"date_gmt":1121,"guid":1122,"modified":1124,"modified_gmt":1125,"slug":1126,"status":14,"type":15,"link":1127,"title":1128,"content":1130,"excerpt":1132,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1134,"categories":1135,"application":1136,"class_list":1137,"acf":1139,"_links":1170},777,"2016-04-01T17:39:32","2016-04-01T21:39:32",{"rendered":1123},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=777","2026-01-26T12:07:47","2026-01-26T17:07:47","2016-guide-to-survey-and-clearance-of-underwater-explosive-ordnance","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2016\u002F04\u002F01\u002F2016-guide-to-survey-and-clearance-of-underwater-explosive-ordnance\u002F",{"rendered":1129},"2016 Guide To Survey and Clearance of Underwater Explosive Ordnance",{"rendered":1131,"protected":21},"\u003Ch1>\u003Cstrong>A Guide to Survey and Clearance of Underwater Explosive Ordnance\u003C\u002Fstrong>\u003C\u002Fh1>\n\u003Cp>This guide focuses on providing a collection of current policy and best practices used in survey and clearance of underwater explosive ordnance. Specific cases are used; they provide examples and analysis. It is not intended to be a comprehensive database of policies and practices; it provides national authorities and mine action organisations (sic) with guidance to better understand the issues and complexities of underwater EO survey and clearance operations.\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"https:\u002F\u002Fwww.gichd.org\u002Fpublications-resources\u002Fpublications\u002Fa-guide-to-survey-and-clearance-of-underwater-explosive-ordnance\u002F\">2016 report\u003C\u002Fa> from Geneva International Centre for Humanitarian Demining (GICHD).\u003C\u002Fp>\n",{"rendered":1133,"protected":21},"\u003Cp>A Guide to Survey and Clearance of Underwater Explosive Ordnance This guide focuses on providing a collection of current policy and best practices used in survey and clearance of underwater explosive ordnance. Specific cases are used; they provide examples and analysis. It is not intended to be a comprehensive database of policies and practices; it […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[332],[1138,15,36,37,38,39,335,336],"post-777",{"external_link":1140,"hero_media":1141,"credits":28,"related_products":1169},"https:\u002F\u002Fwww.gichd.org\u002Fpublications-resources\u002Fpublications\u002Fa-guide-to-survey-and-clearance-of-underwater-explosive-ordnance\u002F",{"width":340,"height":341,"file":1142,"filesize":1143,"sizes":1144,"image_meta":1165,"id":1167,"url":1168},"2025\u002F04\u002F2016-ExplosiveGuide.png",848879,{"medium":1145,"large":1149,"thumbnail":1153,"medium_large":1157,"chip":1161},{"file":1146,"width":50,"height":347,"mime-type":183,"filesize":1147,"url":1148},"2016-ExplosiveGuide-300x200.png",70770,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002F2016-ExplosiveGuide-300x200.png",{"file":1150,"width":57,"height":352,"mime-type":183,"filesize":1151,"url":1152},"2016-ExplosiveGuide-1024x683.png",564021,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002F2016-ExplosiveGuide-1024x683.png",{"file":1154,"width":63,"height":63,"mime-type":183,"filesize":1155,"url":1156},"2016-ExplosiveGuide-150x150.png",30516,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002F2016-ExplosiveGuide-150x150.png",{"file":1158,"width":68,"height":361,"mime-type":183,"filesize":1159,"url":1160},"2016-ExplosiveGuide-768x512.png",355195,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002F2016-ExplosiveGuide-768x512.png",{"file":1162,"width":86,"height":86,"mime-type":183,"filesize":1163,"url":1164},"2016-ExplosiveGuide-100x100.png",14919,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002F2016-ExplosiveGuide-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1166},[],907,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002F2016-ExplosiveGuide.png",[909],{"self":1171,"collection":1176,"about":1178,"author":1180,"replies":1182,"version-history":1185,"predecessor-version":1188,"acf:post":1192,"wp:attachment":1194,"wp:term":1197,"curies":1202},[1172],{"href":1173,"targetHints":1174},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F777",{"allow":1175},[111],[1177],{"href":114},[1179],{"href":117},[1181],{"embeddable":120,"href":121},[1183],{"embeddable":120,"href":1184},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=777",[1186],{"count":927,"href":1187},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F777\u002Frevisions",[1189],{"id":1190,"href":1191},908,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F777\u002Frevisions\u002F908",[1193],{"embeddable":120,"href":935},[1195],{"href":1196},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=777",[1198,1200],{"taxonomy":143,"embeddable":120,"href":1199},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=777",{"taxonomy":146,"embeddable":120,"href":1201},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=777",[1203],{"name":150,"href":151,"templated":120},{"id":1205,"date":1206,"date_gmt":1207,"guid":1208,"modified":1210,"modified_gmt":1211,"slug":1212,"status":14,"type":15,"link":1213,"title":1214,"content":1216,"excerpt":1218,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1220,"categories":1221,"application":1222,"class_list":1223,"acf":1225,"_links":1256},771,"2015-04-30T17:32:16","2015-04-30T21:32:16",{"rendered":1209},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=771","2026-01-26T11:52:45","2026-01-26T16:52:45","2015-technology-demonstration-report","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2015\u002F04\u002F30\u002F2015-technology-demonstration-report\u002F",{"rendered":1215},"2015 Technology Demonstration Report",{"rendered":1217,"protected":21},"\u003Cp>\u003Cstrong>Technology Demonstration Report (TDR) for underwater survey equipment in support of Explosive Remnants of War (EWR) technical survey operations.\u003C\u002Fstrong>\u003C\u002Fp>\n\u003Cp>Marine Magnetics’ \u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fproducts\u002Fmarine-gradiometers\u002Fseaquest2\u002F\">SeaQuest\u003C\u002Fa> and \u003Ca href=\"https:\u002F\u002Fmarinemagnetics.com\u002Fproducts\u002Fmarine-magnetometers\u002Fauv\u002F\">AUV\u002FASV Explorer\u003C\u002Fa> were demonstrated in this \u003Ca href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FGeneva-International-Centre-for-Humanitarian-Demining-GICHD-TDR-15-01FINAL.pdf\">2015 report\u003C\u002Fa> from Geneva International Centre for Humanitarian Demining (GICHD).\u003C\u002Fp>\n",{"rendered":1219,"protected":21},"\u003Cp>Marine Magnetics’ SeaQuest and AUV\u002FASV Explorer were demonstrated in this 2015 report from Geneva International Centre for Humanitarian Demining (GICHD).\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[611,713,332],[1224,15,36,37,38,39,335,616,716,336],"post-771",{"external_link":1226,"hero_media":1227,"credits":28,"related_products":1255},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002FGeneva-International-Centre-for-Humanitarian-Demining-GICHD-TDR-15-01FINAL.pdf",{"width":340,"height":341,"file":1228,"filesize":1229,"sizes":1230,"image_meta":1251,"id":1253,"url":1254},"2024\u002F07\u002F2015-TechnologyDemonstration-Thumb.png",977553,{"medium":1231,"large":1235,"thumbnail":1239,"medium_large":1243,"chip":1247},{"file":1232,"width":50,"height":347,"mime-type":183,"filesize":1233,"url":1234},"2015-TechnologyDemonstration-Thumb-300x200.png",82243,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002F2015-TechnologyDemonstration-Thumb-300x200.png",{"file":1236,"width":57,"height":352,"mime-type":183,"filesize":1237,"url":1238},"2015-TechnologyDemonstration-Thumb-1024x683.png",586992,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002F2015-TechnologyDemonstration-Thumb-1024x683.png",{"file":1240,"width":63,"height":63,"mime-type":183,"filesize":1241,"url":1242},"2015-TechnologyDemonstration-Thumb-150x150.png",35283,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002F2015-TechnologyDemonstration-Thumb-150x150.png",{"file":1244,"width":68,"height":361,"mime-type":183,"filesize":1245,"url":1246},"2015-TechnologyDemonstration-Thumb-768x512.png",372048,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002F2015-TechnologyDemonstration-Thumb-768x512.png",{"file":1248,"width":86,"height":86,"mime-type":183,"filesize":1249,"url":1250},"2015-TechnologyDemonstration-Thumb-100x100.png",17900,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002F2015-TechnologyDemonstration-Thumb-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1252},[],909,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2024\u002F07\u002F2015-TechnologyDemonstration-Thumb.png",[542,909],{"self":1257,"collection":1262,"about":1264,"author":1266,"replies":1268,"version-history":1271,"predecessor-version":1274,"acf:post":1278,"wp:attachment":1281,"wp:term":1284,"curies":1289},[1258],{"href":1259,"targetHints":1260},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F771",{"allow":1261},[111],[1263],{"href":114},[1265],{"href":117},[1267],{"embeddable":120,"href":121},[1269],{"embeddable":120,"href":1270},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=771",[1272],{"count":297,"href":1273},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F771\u002Frevisions",[1275],{"id":1276,"href":1277},910,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F771\u002Frevisions\u002F910",[1279,1280],{"embeddable":120,"href":935},{"embeddable":120,"href":579},[1282],{"href":1283},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=771",[1285,1287],{"taxonomy":143,"embeddable":120,"href":1286},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=771",{"taxonomy":146,"embeddable":120,"href":1288},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=771",[1290],{"name":150,"href":151,"templated":120},{"id":1292,"date":1293,"date_gmt":1294,"guid":1295,"modified":1297,"modified_gmt":1298,"slug":1299,"status":14,"type":15,"link":1300,"title":1301,"content":1303,"excerpt":1305,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1307,"categories":1308,"application":1309,"class_list":1310,"acf":1312,"_links":1344},749,"2015-04-27T16:54:56","2015-04-27T20:54:56",{"rendered":1296},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=749","2025-12-02T16:07:37","2025-12-02T21:07:37","high-resolution-magnetics-in-marine-exploration","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2015\u002F04\u002F27\u002Fhigh-resolution-magnetics-in-marine-exploration\u002F",{"rendered":1302},"High Resolution Magnetics in Marine Exploration",{"rendered":1304,"protected":21},"\u003Cblockquote>\u003Cp>The Acquisition of marine magnetic data on seismic exploration vessels has increased dramatically over the last five years. More sensitive magnetometer equipment, combined with new software processing methods are proving that marine magnetic data can enhance 3-D seismic geological interpretations. The author journeys aboard a seismic research vessel with a crew from FUGRO-LCT, and describes how Sea SPY Overhauser magnometers are used to enhance exploration geological\u002Fgeophysical data models.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>The continuing search for new oilfields relies primarily on using seismic methods to analyze the geology of a region. In recent years, 3-D seismic visualization models have improved the oil and gas exploration process tremendously. This advancement has only strengthened the demand for further improvement. A marine seismic survey is an impressive operation by any standards, both in terms of organization and cost. One survey can involve a fleet of vessels, equipped with millions of dollars worth of equipment and instrumentation. The concept of significantly increasing the quality of results for the relatively small cost of magnetic survey equipment can be attractive. But convincing seismic surveyors to change their ways to accommodate a new sensing method can be difficult, if not impossible. The only way that marine magnetic data can be acquired in conjunction with a seismic survey is if the magnetometer equipment does not interfere in any way with the seismic equipment. The environment is set by the seismic procedures. The magnetics personnel and instrumentation must adapt.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_713\" class=\"wp-caption aligncenter\">\n\u003Cdiv id=\"attachment_713\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.45.38-PM.png\" rel=\"attachment wp-att-713\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-713\" class=\"wp-image-713\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.45.38-PM.png\" alt=\"Screen Shot 2015-10-29 at 4.45.38 PM\" width=\"500\" height=\"345\" aria-describedby=\"caption-attachment-713\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-713\" class=\"wp-caption-text\">Integrated 3D Earth Model.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003Ch2>Coping with the environment\u003C\u002Fh2>\n\u003Cp>To survey a geological area, the area must be broken down into a pattern of parallel lines, along which the vessel must navigate. 3- D seismic surveys usually cover smaller areas than 2-D surveys, but it is still not unusual to see survey lines 100km or more in length. With the vessel averaging about 5 knots, one line can take more than 11 hours, during which the magnetometer must run continuously. A few hours can usually be used for diagnostics and repair while changing lines, but the equipment is expected to operate continuously for weeks at a time. Meanwhile, the vessel is isolated at sea, and it is very difficult to bring in spare parts. An equipment failure here would be a huge and costly problem, so reliability is the number one priority.\u003C\u002Fp>\n\u003Ch2>Long term operation\u003C\u002Fh2>\n\u003Cp>When acquiring magnetic data over a long time period, absolute accuracy becomes very important. Overhauser magnetometers like SeaSPY do not drift due to effects such as temperature, time, or even magnetic heading. However, the Earth’s magnetic field is continually fluctuating, mostly because of influence from the sun. This effect, known as diurnal variation, can slowly affect the absolute value of the Earth’s field by hundreds of nT (nanoTesla) over the course of a day. This is 4 to 5 orders of magnitude greater than the sensitivity of the magnetometer.\u003C\u002Fp>\n\u003Cp>Since diurnal variations affect large areas of the Earth uniformly, it is possible to remove them by using a stationary reference magnetometer, known as a base station. Ideally, the base station should be positioned in the center of the survey area, but in practice, it is usually installed on shore as close to the survey area as possible.\u003C\u002Fp>\n\u003Ch2>Coping with the other players\u003C\u002Fh2>\n\u003Cp>The main sensing element in a seismic survey is the streamer cable, a liquid-filled flexible tube that contains an array of hydrophones. A single 3-D survey vessel will typically trawl between 4 and 12 streamer cables, each about 2.5km in length. The array of streamers is deployed so that the hydrophones are arranged in a tightly controlled grid pattern in the horizontal plane.\u003C\u002Fp>\n\u003Cp>Each of the streamer cables costs millions of dollars, so obviously physical contact with anything is not acceptable. When deploying a towed magnetometer, the first priority is to make sure it stays away from the streamers. FUGRO-LCT does this by using buoyant tow cable developed and supplied by Marine Magnetics. The cable contains a floatation foam that keeps it at the surface, and weight inside the towfish then brings it to a shallow depth away from the swell. Keeping the tow cable out of the way at the surface allows very long cable lengths to be deployed without risk of contacting the streamers, which are typically 10m below the surface. Ideally, the magnetometer cable should be towed at a distance of three times the length of the vessel, to be clear of the vessel’s magnetic interference.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_714\" class=\"wp-caption aligncenter\">\n\u003Cdiv id=\"attachment_714\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.47.47-PM.png\" rel=\"attachment wp-att-714\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-714\" class=\"wp-image-714\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.47.47-PM.png\" alt=\"Screen Shot 2015-10-29 at 4.47.47 PM\" width=\"500\" height=\"326\" aria-describedby=\"caption-attachment-714\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-714\" class=\"wp-caption-text\">Closeup of impact damage sustained during a week-long continuous deployment in the Gulf of Mexico. The signs of impact were only discovered when the towfish was retrieved, since the magnetometer was not affected operationally. Further obstacles are the large powerful airguns, trawled by floating umbilicals, that generate the sound pulses the hydrophones listen for. The guns are normally deployed about 35m behind the vessel, while the magnetometer is kept at a distance of 250m. Some surveys have the guns deployed from a completely separate vessel, which makes magnetometer deployment slightly easier.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003Ch2>The deployment process\u003C\u002Fh2>\n\u003Cp>The seismic streamers are deployed first, starting with the tailbuoy, by large paravanes that keep the streamer away from the ship during deployment.\u003C\u002Fp>\n\u003Cp>Once the streamers are in place, the magnetometer can be deployed. Since an even number of streamers is used during a 3-D seismic survey, there is usually a clear path straight aft of the vessel, and this is where the magnetometer is placed while trawling. A winch is always used to speed deployment and retrieval. From the winch, a deck leader extends the tow connection to a control room where the data logging equipment is stored, along with gravity meters that are almost always used in conjuction with a magnetometer survey on a seismic vessel.\u003C\u002Fp>\n\u003Cp>The airguns are deployed only when the magnetometer is in place. This is where the buoyancy of the magnetometer tow cable does its job. With the cable visible at the surface, the guns can be deployed around it, and kept clear of it.\u003C\u002Fp>\n\u003Ch2>Ruggedness Requirements\u003C\u002Fh2>\n\u003Cp>Having the magnetometer tow cable at the surface leaves it free to contact other objects, such as debris. To protect against this, the tow cable has a thick polyurethane jacket, and the towfish is covered with polyurethane ‘armour’ for high abrasion resistance and impact toughness. At times, the towfish has suffered severe impact from unknown objects, and the survey has continued without interruption.\u003C\u002Fp>\n\u003Ch2>Tow Cable Dynamics\u003C\u002Fh2>\n\u003Cp>Keeping the tow cable at the surface keeps it straight along its deployment length, not curved as it would be if it were allowed to sink gradually to a deep towfish depth. As the vessel moves up and down on the swell, there is little elasticity in the towing system to dampen movement in the towfish. A severe sea state can not only add periodic position error to magnetic data, but can also severely wear the tow cable and connection assembly as slack is constantly created, and taken up suddenly.\u003C\u002Fp>\n\u003Cp>Increasing the towfish drag in the water dampens peaks in the towing force by increasing the average towing force. Adding drag to the towfish also increases its natural towing depth, which is otherwise affected by towing speed and the buoyancy of the cable. This is easily adjusted by increasing the weight of the towfish, or by fastening extra lead weight to the tow cable itself. With increased tow force damping, position error becomes highly correlated to the position of the ship, and is easily eliminated by a good positioning system.\u003C\u002Fp>\n\u003Cp>With a long cable length deployed, high towfish drag, and a rough sea state, steady stress on the towing system can be considerable. To prevent failure under even the most extreme conditions, the tow cable uses a very high performance vectran strength member that is stiffer than kevlar, giving it a high working load, and allowing it to keep a relatively small diameter and weight. A S e a S P Y m a g n etometer transmits data digitally over the tow cable, and its communication system does not use high frequencies, so an elastic twisted pair configuration is used instead of more fragile coax.\u003C\u002Fp>\n\u003Ch2>Using the data\u003C\u002Fh2>\n\u003Cp>Marine magnetometer data contains important geological information such as the thickness of sediments, the locations of faults, and the aerial extent of volcanic rocks. In frontier exploration areas marine magnetics and gravity data are often combined to provide a low cost regional exploration tool for the delineation of large basins prior to conducting expensive seismic surveys. In more mature exploration environments marine magnetics data are often combined with gravity, seismic and well log data to generate an integrated geophysical interpretation of the prospect.\u003C\u002Fp>\n\u003Ch2>Fusing data sources\u003C\u002Fh2>\n\u003Cp>The first step in conducting an integrated geophysical interpretation is the construction of a hypothetical 3D geologic earth model of the prospect using the magnetic, gravity, seismic and well data as an initial qualitative guide for the shapes and sizes of the geologic structures. The earth model consists of a bathymetry layer, geologic horizons, and faults with each layer of the model having a unique set of physical rock properties including density, velocity and susceptibility. After computing the magnetic, gravitational and seismic response of the model, the explorationist analyzes the similarities and differences between the computer generated responses and data that was measured in the field. In areas where the computed model and measured data are in good agreement the explorationist can have a high degree of confidence in the validity of the earth model. In areas where the computed model and measured data are not in good agreement the explorationist is free to change the earth model until the computed response matches that of the measured data.\u003C\u002Fp>\n\u003Cp>As magnetics data provides an independent measurement of a specific rock property (susceptibility or ferrous mineral content) its integration with other data such as gravity, seismic and well log data that measure different rock properties yields a more highly constrained earth model. A well integrated and constrained earth model enables the explorationist to reduce exploration risks. Advances in marine magnetometer equipment and increases in the utilization of the magnetics method at sea have played an important role in both the reduction of exploration costs, and the reliability of geologic interpretations.\u003C\u002Fp>\n",{"rendered":1306,"protected":21},"\u003Cp>Aboard modern seismic vessels, SeaSPY magnetics add a new layer of clarity—strengthening 3-D interpretations without complicating the survey.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[713],[1311,15,36,37,38,39,614,716],"post-749",{"external_link":28,"hero_media":1313,"credits":1341,"related_products":1342},{"width":340,"height":341,"file":1314,"filesize":1315,"sizes":1316,"image_meta":1337,"id":1339,"url":1340},"2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration.png",1078991,{"medium":1317,"large":1321,"thumbnail":1325,"medium_large":1329,"chip":1333},{"file":1318,"width":50,"height":347,"mime-type":183,"filesize":1319,"url":1320},"High-Resolution-Magnetics-in-Marine-Exploration-300x200.png",75569,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration-300x200.png",{"file":1322,"width":57,"height":352,"mime-type":183,"filesize":1323,"url":1324},"High-Resolution-Magnetics-in-Marine-Exploration-1024x683.png",686973,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration-1024x683.png",{"file":1326,"width":63,"height":63,"mime-type":183,"filesize":1327,"url":1328},"High-Resolution-Magnetics-in-Marine-Exploration-150x150.png",30986,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration-150x150.png",{"file":1330,"width":68,"height":361,"mime-type":183,"filesize":1331,"url":1332},"High-Resolution-Magnetics-in-Marine-Exploration-768x512.png",412587,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration-768x512.png",{"file":1334,"width":86,"height":86,"mime-type":183,"filesize":1335,"url":1336},"High-Resolution-Magnetics-in-Marine-Exploration-100x100.png",14595,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1338},[],883,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetics-in-Marine-Exploration.png","\u003Cp>Doug Hrvoic, President and Co-founder of Marine Magnetics Corporation\u003C\u002Fp>\n",[1343],98,{"self":1345,"collection":1350,"about":1352,"author":1354,"replies":1356,"version-history":1359,"predecessor-version":1362,"acf:post":1366,"wp:attachment":1369,"wp:term":1372,"curies":1377},[1346],{"href":1347,"targetHints":1348},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F749",{"allow":1349},[111],[1351],{"href":114},[1353],{"href":117},[1355],{"embeddable":120,"href":121},[1357],{"embeddable":120,"href":1358},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=749",[1360],{"count":273,"href":1361},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F749\u002Frevisions",[1363],{"id":1364,"href":1365},884,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F749\u002Frevisions\u002F884",[1367],{"embeddable":120,"href":1368},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fproduct\u002F98",[1370],{"href":1371},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=749",[1373,1375],{"taxonomy":143,"embeddable":120,"href":1374},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=749",{"taxonomy":146,"embeddable":120,"href":1376},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=749",[1378],{"name":150,"href":151,"templated":120},{"id":1380,"date":1381,"date_gmt":1382,"guid":1383,"modified":1385,"modified_gmt":1386,"slug":1387,"status":14,"type":15,"link":1388,"title":1389,"content":1391,"excerpt":1393,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1395,"categories":1396,"application":1397,"class_list":1398,"acf":1400,"_links":1431},30,"2011-01-01T14:51:00","2011-01-01T19:51:00",{"rendered":1384},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=30","2026-02-12T17:23:53","2026-02-12T22:23:53","mapping-marine-ferrous-targets-using-the-seaquest-gradiometer-system","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2011\u002F01\u002F01\u002Fmapping-marine-ferrous-targets-using-the-seaquest-gradiometer-system\u002F",{"rendered":1390},"Mapping Marine Ferrous Targets Using the SeaQuest Gradiometer System",{"rendered":1392,"protected":21},"\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System.pdf\">Download Original Article\u003C\u002Fa>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Cp>In June 2003, the Naval Undersea Warfare Center (NUWC), Keyport WA, surveyed a small waterway within Puget Sound using a SeaQuest gradiometer system. The goal of the survey was to determine the suitability of the site as a location for the U.S. Navy’s new Electro-Magnetic Field Measurement (EMFM) System, consisting of several stationary magnetic and electric field measurement sensors.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1404\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.04-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1404\" class=\"wp-image-1404\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.04-AM.png\" width=\"500\" height=\"239\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1404\" class=\"wp-caption-text\">Figure 1: Location of survey site\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>The purpose of the EMFM system is to measure the relatively small electromagnetic signatures of unmanned undersea vehicles, so selection of a magnetically quiet location was crucial to the success of the project. The area was deemed likely to contain quantities of scrap metal from historical and industrial activities (such as the nearby torpedo testing range) that could interfere with the operation of the EMFM system. The objective of the survey was to locate the geographic position and depth of burial of all ferro-metallic objects within the survey area that would generate anomalies greater than one nanoTesla (nT) and gradients greater than 3 nT\u002Fm at a distance of less than 25 m. With that information, the optimum locations for the EMFM System sensors could then be determined.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1403\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.22-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1403\" class=\"wp-image-1403\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.22-AM.png\" width=\"500\" height=\"350\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1403\" class=\"wp-caption-text\">Figure 2: The SeaQuest three-axis gradiometer system\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>Marine Magnetics’ SeaQuest system, the only commercially available three component marine gradiometer platform, was chosen for this project since it offers several advantages over total-field sensors and conventional (single axis) magnetic gradiometers. SeaQuest is capable of measuring the transverse, vertical, and longitudinal gradient of the ambient field simultaneously, which allows direct calculation of the Total Magnetic Gradient (a.k.a. Analytic Signal, see Roest et al., 1992)\u003Csup id=\"fnref11\">\u003Ca href=\"#fn11\">1\u003C\u002Fa>\u003C\u002Fsup> in real time. This greatly reduces post processing time and increases survey accuracy, since the measured total gradient data is free of diurnal variation, as well as immune to the unpredictable effects of permanently magnetized sources and an inclined ambient field. (For a detailed discussion on the threory of total-field gradiometry see the Background Theory section at the conclusion of this document).\u003C\u002Fp>\n\u003Cp>Most importantly, the total gradient information enhances near-surface anomalies (such as man-made steel objects) and greatly simplifies the complex three-dimensional information provided by magnetic field data into an easy to interpret form.\u003C\u002Fp>\n\u003Cp>The presented results demonstrate the inherent advantages of measuring all three components of the magnetic gradient vector and interpreting total gradient data when attempting to quickly locate the position and depth of ferro-metallic objects. The total gradient data allowed easy identification of several targets in the survey area that otherwise would have been missed by conventional survey methods due to geologically sourced magnetic anomalies.\u003C\u002Fp>\n\u003Ch2>Instrument Description\u003C\u002Fh2>\n\u003Cp>The Marine Magnetics SeaQuest system (Figure 2) used in this study consists of a three-sensor biaxial platform that measures transverse horizontal gradient over a baseline of 1.5 m, and vertical gradient over a baseline of 0.5 m. Real-time longitudinal gradient measurement is accomplished by comparing successive total-field measurements to each other using their relative GPS positions along the survey track, or by adding a fourth sensor to the platform tail if higher precision is required. Alternatively the unit may be operated in tandem with a SeaSPY magnetometer for long-baseline measurement. For this study a 3-sensor configuration was used.\u003C\u002Fp>\n\u003Cp>SeaQuest’s most important characteristic is the superb absolute accuracy of its Overhauser sensors. If a magnetic gradiometer displays even minute absolute shifts between its sensors, either due to heading effects or systemmatic inaccuracy, it is impossible to correlate adjacent survey lines, and also to relate multiple axis gradient measurements into a single total gradient result (see Equation 1 on page 5). Complex manual adjustment must then be applied post-survey, introducing a major source of error. The SeaQuest system eliminates this error with its Overhauser sensors that are repeatable to better than 0.01 nT, and show zero detectable heading error.\u003C\u002Fp>\n\u003Cp>SeaQuest’s Overhauser sensors are also free from ‘dead zones’ which complicate the use of alkali-vapour sensors. Sensors that have a dead zone must be oriented correctly with respect to the inclination of the ambient field in order to produce valid data. This is particularily problematic at mid to low latitudes, where even an optimally oriented sensor will fail to produce data in certain survey line directions.\u003C\u002Fp>\n\u003Cp>Another important characteristic is platform stability. Since it is measuring a directional quantity that is heavily dependent on distance from the magnetic source, a gradiometer must provide accurate spatial position data for its sensors. SeaQuest incorporates an acoustic altimeter and pressure sensor to report its vertical position in the water column, and an accurate 2-axis tilt sensor to report pitch and roll. Most importantly, the platform is extremely hydrodynamically stable, which minimizes the need for dynamic compensation for motion effects.\u003C\u002Fp>\n\u003Cp>SeaQuest provides a base noise spectral density of 0.01 nT-RMS\u002Frt-Hz per sensor. This translates to roughly 0.009 nT\u002Fm noise in horizontal gradient, and 0.028 nT\u002Fm noise in vertical gradient. Relating noise levels to actual detectable changes requires us to define a threshold signal-to-noise ratio (SNR) that we can use to identify anomalies. If a SNR of 10 is used to define our minimum detection levels, SeaQuest’s practical magnetic gradient detection levels are 0.1 nT\u002Fm horizontal and about 0.25 nT\u002Fm vertical. This is an order of magnitude finer than the deviation one would see from gradiometers based on other technologies simply by rotating them in place, and measuring their heading error.\u003C\u002Fp>\n\u003Cp>It is important to note that SeaQuest produces raw data that is not filtered – the frequency response extends evenly to the Nyquist frequency, which is the maximum theoretical frequency that data can represent. Filtering the data to a lower bandwidth, a common practice for faster sampling optically pumped magnetometers to reduce the apparent noise level, introduces phase shifts into the data that are different for each frequency being measured. This makes it impossible to correlate signals measured by independent total field sensors, and form an accurate three-dimensional total gradient result.\u003C\u002Fp>\n\u003Ch2>Survey Parameters\u003C\u002Fh2>\n\u003Cp>The gradiometer survey was conducted over a two-day period, in addition to side scan sonar and multibeam acquisition. A total of 12 hours survey time were required for the gradiometer.\u003C\u002Fp>\n\u003Cp>The survey vessel was a civilian-crewed, wooden-hulled U.S. Navy officer training ship adapted for survey work. SeaQuest was deployed 100 m astern to insure that the magnetic influence of the ship was negligible at the sensor position. The instantaneous depth, altitude, pitch and roll of the tow body were recorded with each magnetic gradient sample.\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.35-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1402\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.35-AM.png\" width=\"500\" height=\"266\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>The survey positions were acquired by a Trimble RTK GPS system and adjusted by a Sonardyne USBL transponder. The transponder unit was battery powered, and was mounted on the SeaQuest tow cable 2m forward of the tow body to prevent the transponder’s magnetic effect being measured by the gradiometer. Positioning error was determined to be less than 1m. The adjusted position data was integrated in real time into the SeaQuest data stream by the SeaQuest logging software. Survey lines were created and displayed with QINSy software by QPS.\u003C\u002Fp>\n\u003Cp>The survey block consisted of 26 East-West survey lines, nominally spaced at 25m collected in a racetrack fashion over the 650 x 1000m site. Two North-South tie-lines were collected for quality control purposes. In this survey design the measured transverse gradient corresponds to the y-gradient (North-South component of the total gradient) and the longitudinal (along-track) gradient corresponds to the xgradient (East-West component). The vertical gradient is also subsequently referred to as the z-gradient.\u003C\u002Fp>\n\u003Cp>The water depth in the survey block varied considerably, with shallow water at the edges and deeper water in the center. A relatively constant pressure depth was used for the bulk of the survey, and vessel speed was increased slightly during line change, allowing SeaQuest to rise over the shallow areas when needed. Figure 3 shows a map of the area bathymetry, calculated with data from the SeaQuest altimeter and pressure sensor. Tide deviation was corrected manually.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1401\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.43-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1401\" class=\"wp-image-1401\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.43-AM.png\" width=\"500\" height=\"210\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1401\" class=\"wp-caption-text\">Figure 3: Area Bathymetric Map. Survey lines spanned the entire width and height of the above map, but the ridge to the east was dominated by strong geological magnetism, and was determined to be inappropriate for the Navy’s needs in placement of their AUV-monitoring sensors.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>Data Processing\u003C\u002Fh2>\n\u003Cp>After the survey, the recorded data was imported into Geosoft’s Oasis Montaj software, a package commonly used for professional-quality magnetic data processing and interpretation. As with a typical magnetometer survey, data was evaluated and edited on a line-by-line basis for quality control purposes. Magnetic data was gridded using the minimum curvature method (Briggs, 1977) with a 5m cell size.\u003Csup id=\"fnref1\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cp>Very little processing was required to present the data in the form given in this paper, due in large part to the magnetic cleanliness of the SeaQuest platform, and the high accuracy of the Overhuaser sensors. These characteristics eliminated the need for complex and error-prone filtering and level-shifting operations necessary to obtain usable results with other magnetic gradiometers.\u003C\u002Fp>\n\u003Cp>Grids were created directly from measured data only. No compensation for diurnal effect was required, and no heading or altitude compensation was applied. The grids produced were (1)Total field, (2)Xgradient, (3)Y-gradient, (4)Z-gradient and (5)Total-Gradient. The production of the X and Y gradient grids required the data to have the appropriate sign correction applied to account for opposite survey line directions.\u003C\u002Fp>\n\u003Cp>The total gradient data (calculated by the SeaQuest acquisition software during the survey), is mathematically equivalent to the Analytic Signal. It is a simple conversion from Cartesian to polar coordinates, and can be described as:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.51-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-1400\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.57.51-AM.png\" width=\"500\" height=\"172\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>where B is the ambient magnetic field, and dB\u002Fdx, dB\u002Fdy, and dB\u002Fdz are the spatial derivatives (gradients) of the total field in the three Cartesian axes x,y,z. All three of these gradients are measured directly by  SeaQuest, making the calculation of total gradient very simple. This operation reduces the magnetic data to anomalies whose maxima mark the edges of magnetized bodies, as well as centering the anomalies over the source bodies (Roest et al., 1992).\u003Csup id=\"fnref4\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cp>Targets were identified by using the Blakely algorithm (Blakely and Simpson, 1986) to automatically find peaks in the gridded total gradient data. \u003Csup id=\"fnref2\">\u003C\u002Fsup>This test compares the values of each grid cell to the values of its neighboring cells. If the current cell has a value higher than all of its adjacent cells it is selected as a target, and its geographic position is recorded to a target list. Targets lists were then separated into primary and secondary based on amplitude of the signal, and interpretation of the other data products.\u003C\u002Fp>\n\u003Cp>The apparent depth to the primary targets was calculated by Euler’s homogeneity equation (Euler Deconvolution – Reid et al., 1990) using the produced x, y and z gradient grids from the measured data.\u003Csup id=\"fnref3\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Ch2>Results\u003C\u002Fh2>\n\u003Cp>The following pages show the striking contrast between conventional magnetometer (total field) data and the high resolution gradient data obtainable with SeaQuest.\u003C\u002Fp>\n\u003Cp>Figure 4 shows the total magnetic field data collected by the top sensor of the SeaQuest platform. This image represents data that would be obtainable by a conventional total field survey and is presented for comparison purposes. The total field image is dominated by north-south trending curvilinear anomalies, which are likely related to magnetic susceptibility variations in the bedrock. This strong background magnetic response makes it difficult to quickly identify anomalies associated with ferrous objects. The amplitudes of these curvilinear anomalies increase eastward suggesting that the depth to bedrock is decreasing eastward. Presenting the total field grid with a ‘stretched’ colour-scale allows identification of at least four potential ferrous targets in the western half of the survey site (arrows).\u003C\u002Fp>\n\u003Cp>In contrast, the total gradient map (Figure 5) allows easy identification of at least 12 (high-confidence) ferro-magnetic objects within the survey block. The wavelengths associated with the geological magnetic effects are effectively suppressed in this image in comparison to the total field image. Targets are defined by simple ‘bulls-eye type’ positive anomalies, which are centered over the target position. In the western part of the survey block, a low amplitude NNW-trending linear anomaly is present. This anomaly corresponds to a known pipeline marked on the marine charts of the area. It is worth noting that the amplitude of the pipeline anomaly is less than 0.5nT\u002Fm, and yet it is clearly visible in the total gradient map.\u003C\u002Fp>\n\u003Cp>Also of interest is the large anomaly slightly to the east of the center of the map. Despite its size, the anomaly is obscured by geology in the total field data, yet it shows up prominently in the total gradient data.\u003C\u002Fp>\n\u003Cp>For comparison, the three single-component gradient maps are presented in Figure 6. The data generally shows enhancement of short wavelength anomalies that could define targets. However, interpretation of target positions is still complicated by anomalies that are not centered over the source, anomaly distortion, and remaining geological interference.\u003C\u002Fp>\n\u003Cp>It is easy to see that the total gradient (Analytic Signal) directly measured by SeaQuest provides the clearest results, effectively creating an intuituve magnetic ‘image’ of the sea bottom. While the singleaxis gradient results enhance only certain types of anomalies based on their geographic direction, the total gradient is effectively a direction-independent result, enhancing all near-surface anomalies equally, and suppressing deep geology evenly.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1399\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.05-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1399\" class=\"wp-image-1399\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.05-AM.png\" width=\"500\" height=\"310\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1399\" class=\"wp-caption-text\">Figure 4: Total magnetic field map of the NUWC survey site. The image is dominated by North-South trending curvilinear anomalies related to buried geology. Only a few ferro-magnetic targets are identifiable (arrows). The Eastern part of the survey block is dominated by geological noise.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv id=\"attachment_1398\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.20-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1398\" class=\"wp-image-1398\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.20-AM.png\" width=\"500\" height=\"281\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1398\" class=\"wp-caption-text\">Figure 5: Total Magnetic Gradient (analytic signal) map of the NUWC survey site. The deep geological signal is eliminated, and extremely small targets can be easily resolved, including a faint linear feature in the west that was invisible in the total field data. The linear feature corresponds to a known pipeline.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.42-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"wp-image-1397\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.42-AM.png\" width=\"500\" height=\"273\" \u002F>\u003C\u002Fa>\u003Cp class=\"wp-caption-text\">Figure 6: All three measured magnetic gradient axes shown independently. Gradient in the x (East-West) direction. Note enhancement of north-south oriented anomalies. The pipeline in the west of the block is visible, but difficult to interpret.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.52-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"wp-image-1396\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.58.52-AM.png\" width=\"500\" height=\"270\" \u002F>\u003C\u002Fa>\u003Cp class=\"wp-caption-text\">Gradient in the y (North-South) direction. Note enhancement of East-West oriented anomalies. Geology has virtually disappeared because the geological features are N-S trending. However, the pipeline in the west of the block is nearly invisible.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.59.01-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"wp-image-1395\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.59.01-AM.png\" width=\"500\" height=\"271\" \u002F>\u003C\u002Fa>\u003Cp class=\"wp-caption-text\">Gradient in the z (vertical) direction. High frequency features are enhanced relatively equally. Note significant remaining influence of the strong deep geology in the east.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.59.13-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"wp-image-1394\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.59.13-AM.png\" width=\"500\" height=\"287\" \u002F>\u003C\u002Fa>\u003Cp class=\"wp-caption-text\">Figure 7: Interpretation of data products overlaid on grayscale total gradient map. Primary target depth estimates (see triangle symbols) obtained from Euler Deconvolution of the measured gradients. Total gradient grid values of the target position provide an estimate of the relative target\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv id=\"attachment_1393\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.59.25-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1393\" class=\"wp-image-1393\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FScreen-Shot-2018-01-16-at-8.59.25-AM.png\" width=\"500\" height=\"243\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1393\" class=\"wp-caption-text\">Figure 8: Profile view of one line of SeaQuest data over the NUWC survey site. A- Total-field data recorded from the top sensor. B- Measured x, y and z gradients. C- Corresponding total-gradient calculated in real-time, showing significantly improved signal-to-noise ratio of ferrous targets. Point 1- The complex negative-couplet anomaly measured in the total-field is transformed into a positive peak in the total-gradient, indicating the source position. Point 2- The longer wavelength (deeper) magnetic signal in the total-field profile A is not present in the total-gradient profile C, allowing for easier identification of small near surface targets such as at Point 3.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>Conclusions\u003C\u002Fh2>\n\u003Cp>This paper demonstrates the inherent advantages of directly measuring the Total Magetic Gradient over conventional magnetometer and gradiometer techniques, when searching for small ferro-metallic objects.\u003C\u002Fp>\n\u003Cp>Magnetic gradient is commonly used to enhance the signals from small, relatively close sources typical of iron manmade objects, and to suppress the signals from large distant sources associated with geological variation. The total gradient technique goes even further by eliminating the directional dependence of conventional gradiometer methods. This produces an easily interpreted magnetic ‘image’ of the sea floor, with target positions unambiguously marked by ‘bulls-eye’ type anomalies. Also, the total gradient anomalies are expressed with a higher signal-to-background-noise ratio than with conventional techniques, enabling the identification of tiny targets that would otherwise be invisible.\u003C\u002Fp>\n\u003Cp>Since the total gradient grid places positive anomalies directly over the source bodies, it allows target maps to be rapidly and accurately generated by an automated peak-picking algorithm, and allows depth estimates to be efficiently obtained by Euler Deconvolution.\u003C\u002Fp>\n\u003Cp>The SeaQuest gradiometer platform enables the acquisiton of high-quality total gradient data because of its hydrodynamic stability and the high absolute accuracy of its sensors, producing clean results free from heading errors and offsets. Despite high currents and demanding conditions, SeaQuest provided consistent results that did not require the filtering or level-shifting that are necessary steps, yet large sources of calculation error, for other gradiometer instruments.\u003C\u002Fp>\n\u003Cp>What did this mean for the Navy’s goal of placing EMFM sensors for AUV monitoring? SeaQuest revealed a number of magnetic sources that were not detected by acoustic methods, that would have interfered with the Navy’s sensors. The most prominent obstacle was the large anomaly just to the east of the center of the block (Target ID 6 in figure 7).\u003C\u002Fp>\n\u003Cp>The Navy’s original goal was to clear the site of magnetic anomalies if any were found. After the survey, divers were sent to investigate several targets, but visibility was zero due to ocean conditions. Further investigation is planned next year.\u003C\u002Fp>\n\u003Cp>Instead of clearing the site, the Navy moved its test range to the south-eastern end of the survey block where the gradient data indicated a large magnetically homogeneous area. The EMFM sensors were deployed and are now operating correctly.\u003C\u002Fp>\n\u003Ch2>Background Theory\u003C\u002Fh2>\n\u003Cp>Total-field marine magnetometers are routinely used in applications where there is a need to delineate the location and relative size of ferro-metallic objects at or buried below the seabed.\u003C\u002Fp>\n\u003Cp>In small target mapping applications using a conventional magnetometer, data is collected on closely spaced survey lines and interpolated into a gridded-array of data cells and displayed as colour-contoured map formats. Targets are located on the map by identifying anomalous short wavelength and comparatively high amplitude deviations in field intensity, which are superimposed on the regional and ‘background’ field variations. In many cases however, the variations in background field may be considerable in comparison to the very small anomalies that define the targets of interest.\u003C\u002Fp>\n\u003Cp>Near-surface geologically-sourced magnetic variations and solar-sourced “diurnal” magnetic variations are two examples of problematic ‘background’ magnetic signals. This background noise can mask the targets of interest and thus complicate interpretation. This can lead to missed or falsely identified targets in a survey. The interpretation of magnetic field data at mid to low latitudes is further complicated by an ambient field vector that is inclined with respect to the vertical. This results in dipole anomalies that have a complex waveform (i.e. usually a positive deviation followed by a negative deviation). This makes it less intuitive to determine the exact location of source body. In addition, virtually all man made objects have significant permanent magnetization that can further distort the field variations over a target.\u003C\u002Fp>\n\u003Cp>In a conventional magnetometer survey, diurnal variations can be compensated for by the use of a second “base-station” magnetometer. This magnetometer remains stationary for the duration of the survey in order to record the solar-related variations in field intensity so that they can later be removed from the survey data. This correction is essential when the goal of the survey is to produce a high-resolution magnetic map using total-field magnetic data only. However, in marine surveys the use of a base-station magnetometer often complicates the survey logistics and increases costs. For example, finding a suitable location for the base-station, (i.e. that is free of cultural magnetic noise, relatively close to the survey site, and secure enough to leave unattended for a long period of time) can be a major challenge, particularly in urbanized or industrialized locations.\u003Csup id=\"fnref8\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cp>Removing the magnetic effects of geology from survey data is more complex. Often it involves the use of spatial Fourier-domain filters (i.e. upward\u002Fdownward continuation) applied to the total-field grid to remove the wavelengths in the data associated with the geology (Li and Oldenburg,1998). \u003Csup id=\"fnref6\">\u003C\u002Fsup>Several other methods may be successful (i.e. calculation of artificial gradients or the analytic signal from carefully leveled total-field data (Roest et al., 1992). \u003Csup id=\"fnref9\">\u003C\u002Fsup>However, all methods require significant processing time and expertise, resulting in increased costs.\u003C\u002Fp>\n\u003Cp>Compensation for inclination of the Earth’s field can be carried out by reducing the data to the magnetic pole (Aina, 1986).\u003Csup id=\"fnref5\">\u003C\u002Fsup> This filter operation simplifies the vector nature of the field by adjusting the field values to represent data collected in a vertically oriented magnetic field (as at the magnetic pole). This greatly simplifies interpretation, but the process is not stable at low magnetic latitudes (Macleod et al., 1993). \u003Csup id=\"fnref11\">\u003C\u002Fsup>\u003Csup id=\"fnref8\">\u003C\u002Fsup>Furthermore the process requires the assumption of induced magnetization for all anomalies, which is not valid for almost all ferro-magnetic objects.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Gradiometers\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>A gradiometer is a specialized type of magnetometer that measures a gradient, or first spatial derivative of the total magnetic field. Gradiometers usually consist of two sensors separated by a fixed distance. The sensors simultaneously measure the total field strength. The difference in measured intensity is divided by the distance between the sensors (baseline distance) resulting in a linear estimate of the gradient of the ambient field. The orientation of the gradiometer will determine what component of the three-dimensional field is measured (usually the x, y, or vertical components).\u003C\u002Fp>\n\u003Cp>A well designed magnetic gradiometer has a high degree of immunity from diurnal and magnetic storm activity. Short-baseline magnetic gradient data also shows enhancement of small-wavelength near surface anomalies as generated by ferro-metallic objects, and tends to suppress longer wavelength geological anomalies that may interfere in target mapping applications.\u003C\u002Fp>\n\u003Cp>Most commercially available marine gradiometers consist of two synchronized and separated total-field towfish and are limited to measurement of only one gradient component; either the x or y components by transverse or longitudinal configurations. Longitudinal configurations measure the ‘along track’ gradient and consist of the first towfish separated from the second by a length of cable in a ‘single-file’ manner. This gradiometer design is not optimal for target mapping since the separation between the towfish is not rigidly fixed, and thus requires very long baseline distances (i.e. > 20 m) to obtain an accurate gradient measurement.\u003C\u002Fp>\n\u003Cp>Transverse marine gradiometers measure the ‘cross-track’ gradient and have the two towfish separated horizontally by a rigid support system, allowing improved resolution of small, near surface anomalies. However, the design has several drawbacks, including the dependency of the survey line direction on the measured gradient direction, and the inability to resolve the vertical component of the gradient vector. In addition, single component gradient data still requires correction for the inclination of the Earth’s field and permanently magnetized sources in order to result in consistent anomalies that are directly over the source bodies.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>3-Axis Gradient Measurement\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>As demonstrated in this study, the measurement of three independent magnetic gradients of the total field using the SeaQuest multiaxis gradiometer system allows real-time calculation of the total-magnetic gradient of the field as described by Equation 1. This operation reduces the magnetic data to anomalies whose maxima mark the edges of magnetized bodies, as well centering the anomalies over the source bodies regardless of the presence of permanent magnetization or inclination of the ambient field. Since the amplitudes in the total gradient grid are derived from a combination of all vector omponents of the field into a simple constant, it can be thought of as a map of total magnetization in the ground.\u003C\u002Fp>\n\u003Cp>With the SeaQuest system, gradients are measured as instantaneous observations over short base lines and are thus impervious to diurnal magnetic field effects. The calculated total gradient data is therefore also devoid of diurnal field effects, which eliminates the need for the base-station correction. Due to the frequency of the measured gradients and inherent limitation of the sensitivity of magnetometers, very long wavelength magnetic features are lost in the total gradient information. But this is an advantage in target mapping exercises. Long wavelength information is best viewed by using one or all three of the available total-field measurements.\u003C\u002Fp>\n\u003Cp>It is worthwhile to note that data products analogous to the total gradient map in Figure 5 can be produced from single-sensor total field data. It is accepted practice to calculate the Analytic Signal grid, starting with single total field grid (Roest et al., 1992; MacLeod et al., 1993). This process requires calculation of the apparent x, y, and z derivative grids prior to calculation of the analytic signal grid as in Equation 1. However, the results of this process will be vastly inferior to using measured gradient products, and would require a very carefully collected and leveled total field grid in order to create useful results. No matter how good the correction, the results could never approach the quality obtained by the SeaQuest system.\u003C\u002Fp>\n\u003Cp>The SeaQuest system employs many design elements to eliminate or reduce as many sources of error in the total gradient as possible. The rigid spacing of the sensors eliminates relative positioning errors. Sensors are extremely accurate and stable so that the measured difference between them will be consistent and repeatable under all conditions. The platform is hydrodynamically stable, maintaining minimal pitch and roll and therefore eliminating errors due to gradient axis orientation.\u003C\u002Fp>\n\u003Col id=\"footnotes\">\n\u003Cli>\u003Cstrong>Aina, A\u003C\u002Fstrong>., 1986, Reduction to equator, reduction to pole and orthogonal reduction of magnetic profiles: Expl. Geophys., Austr. Soc. Expl. Geophys., \u003Cstrong>17\u003C\u002Fstrong>, 141-145.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Briggs\u003C\u002Fstrong>, 1974, Machine contouring using minimum curvature. Geophysics, \u003Cstrong>39\u003C\u002Fstrong>, 39-48.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Li, Y.\u003C\u002Fstrong> and Oldenburg, D. W., 1998, Separation of regional and residual magnetic field data: Geophysics, \u003Cstrong>63\u003C\u002Fstrong>, 431-439.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>MacLeod, I. N., Vierra, S., Chavew, A. C.\u003C\u002Fstrong>, 1993, Analytic signal and reduction-to-the- pole in the interpretation of total magnetic field data at low magnetic latitudes, Proceedings of the third international congress of the Brazillian society of geophysics.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Reid, A. B., Allsop, J. M., Granser, H., Millett, A. J., Somerton, I. W.\u003C\u002Fstrong>, 1990, Magnetic interpretation in three dimensions using Euler deconvolution: Geophysics, \u003Cstrong>55\u003C\u002Fstrong> (1), 80-91.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Roest, W. R., Verhoef, J. and Pilkington, M.\u003C\u002Fstrong>, 1992, Magnetic interpretation using the 3-D analytic signal : Geophysics, \u003Cstrong>57\u003C\u002Fstrong>, 116-125.\u003C\u002Fli>\n\u003C\u002Fol>\n",{"rendered":1394,"protected":21},"\u003Cp>Marine Magnetics’ SeaQuest system, the only commercially available three component marine gradiometer platform, was chosen for this project since it offers several advantages over total-field sensors and conventional magnetic gradiometers.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[611,713,332],[1399,15,36,37,38,39,614,616,716,336],"post-30",{"external_link":28,"hero_media":1401,"credits":1429,"related_products":1430},{"width":340,"height":341,"file":1402,"filesize":1403,"sizes":1404,"image_meta":1425,"id":1427,"url":1428},"2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System.png",1908673,{"medium":1405,"large":1409,"thumbnail":1413,"medium_large":1417,"chip":1421},{"file":1406,"width":50,"height":347,"mime-type":183,"filesize":1407,"url":1408},"Mapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-300x200.png",84604,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-300x200.png",{"file":1410,"width":57,"height":352,"mime-type":183,"filesize":1411,"url":1412},"Mapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-1024x683.png",1051693,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-1024x683.png",{"file":1414,"width":63,"height":63,"mime-type":183,"filesize":1415,"url":1416},"Mapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-150x150.png",33964,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-150x150.png",{"file":1418,"width":68,"height":361,"mime-type":183,"filesize":1419,"url":1420},"Mapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-768x512.png",575515,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-768x512.png",{"file":1422,"width":86,"height":86,"mime-type":183,"filesize":1423,"url":1424},"Mapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-100x100.png",16425,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1426},[],676,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2016\u002F07\u002FMapping-Marine-Ferrous-Targets-Using-the-SeaQuest-Gradiometer-System.png","\u003Cp data-start=\"68\" data-end=\"296\">Originally published as \u003Cem data-start=\"96\" data-end=\"184\">Mapping Marine Ferrous Targets Using the SeaQuest Gradiometer System, Rev. 1.3 (2011).\u003Cbr \u002F>\n\u003C\u002Fem>Written by Matthew Pozza and Doug Hrvoic, Marine Magnetics Corporation, Richmond Hill, Ontario, Canada.\u003C\u002Fp>\n",[542],{"self":1432,"collection":1437,"about":1439,"author":1441,"replies":1443,"version-history":1446,"predecessor-version":1450,"acf:post":1454,"wp:attachment":1456,"wp:term":1459,"curies":1464},[1433],{"href":1434,"targetHints":1435},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F30",{"allow":1436},[111],[1438],{"href":114},[1440],{"href":117},[1442],{"embeddable":120,"href":121},[1444],{"embeddable":120,"href":1445},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=30",[1447],{"count":1448,"href":1449},23,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F30\u002Frevisions",[1451],{"id":1452,"href":1453},999,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F30\u002Frevisions\u002F999",[1455],{"embeddable":120,"href":579},[1457],{"href":1458},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=30",[1460,1462],{"taxonomy":143,"embeddable":120,"href":1461},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=30",{"taxonomy":146,"embeddable":120,"href":1463},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=30",[1465],{"name":150,"href":151,"templated":120},{"id":1467,"date":1468,"date_gmt":1469,"guid":1470,"modified":1472,"modified_gmt":1473,"slug":1474,"status":14,"type":15,"link":1475,"title":1476,"content":1478,"excerpt":1480,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1482,"categories":1483,"application":1484,"class_list":1485,"acf":1487,"_links":1518},36,"2008-01-01T14:53:07","2008-01-01T19:53:07",{"rendered":1471},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=36","2026-01-26T12:44:40","2026-01-26T17:44:40","high-resolution-magnetic-target-survey","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2008\u002F01\u002F01\u002Fhigh-resolution-magnetic-target-survey\u002F",{"rendered":1477},"High-Resolution Magnetic Target Survey",{"rendered":1479,"protected":21},"\u003Cblockquote>\u003Cp>Magnetic surveying is a common methodology for small-object detection applications such as UXO clearance, pipeline location and archaeology. Now gradiometers using Overhauser technology are doing the job faster and better by directly measuring the analytic signal – a high-resolution data form that is ideal for resolving small magnetic features and eliminating the unwanted effects of geology and solar interference.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Ch1 class=\"p1\">Harnessing the power of three-axis total-field magnetic gradient\u003C\u002Fh1>\n\u003Cp>Magnetometers have long been used to locate small, buried ferrometallic objects in all varieties of marine environments. Quantum total-magnetic-field sensors based on the wellknown proton or the more recent and powerful Overhauser technology have made the acquisition of stable, good quality, low-noise data relatively easy. The challenge in a target-search application is most often the interpretation of results, specifically the separation of artefacts that are not significant from the beacons that will lead a surveyor to his goals.\u003C\u002Fp>\n\u003Ch2>How We ‘See’ Objects Magnetically\u003C\u002Fh2>\n\u003Cp>A magnetometer measures the Earth’s magnetic field.A ferrometallic object is detectable by a magnetometer because it creates a magnetic field of its own that results in a local deviation in the Earth’s magnetic field. The shape of this deviation is dependent upon both the permanent and induced magnetisation of the ferrous object.The permanent magnetisation of the object may be thought of as the magnetisation acquired by the object when it was cooled from a molten state and will move and reorient with the object; it might therefore point in any direction.The induced magnetisation of the object is a result of the action of the Earth’s magnetic field on the object and is always oriented with the Earth’s field; its magnitude is a scalar function of the Earth’s field.\u003C\u002Fp>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv id=\"attachment_707\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.13.25-PM.png\" rel=\"attachment wp-att-707\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-707\" class=\"wp-image-707\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.13.25-PM.png\" alt=\"Screen Shot 2015-10-29 at 4.13.25 PM\" width=\"500\" height=\"195\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-707\" class=\"wp-caption-text\">Figure 1: Total magnetic effect of a 10kg iron object modelled at a 5m survey altitude using Earth field inclinations of 0, 25 and 45 degrees respectively. North is toward the lower left. The vertical units are nT and the horizontal units are m. Target location is 0,0.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>These two magnetic fields vector-add both with each other and also with the Earth’s ambient magnetic field within the space surrounding the object. This creates quite a complex mathematical combination that is complicated further by the change of the Earth’s field inclination at different latitudes. Furthermore, magnetometer surveys are conducted on relatively horizontal planes that slice through the fields we wish to detect. Consequently, the total-magnetic-field anomalies we measure are often complex in shape, even for the simplest point-source dipole.\u003C\u002Fp>\n\u003Cp>To illustrate, Figure 1 shows 3D plots of the same point-source dipole modelled at a measurement altitude of 5m.The model takes into account induced magnetisation only, at three different Earth field inclinations of 0, 25 and 45 degrees.The Earth field inclination is a function of latitude, so the same target clearly appears different depending on where in the world it is located. Furthermore, the magnetic signal does not have a clear centre and it is not straightforward to pinpoint the target’s precise location.\u003C\u002Fp>\n\u003Cp>This becomes a greater problem when there are multiple small targets close enough together that their fields overlap. Figure 2a shows several iron objects of varying sizes and depths. Some of the objects are close together.The modelled magnetic map (Figure 2b) shows that the total field does not easily resolve all of the target positions; smaller and shallower targets are obscured by the magnetic response of larger and deeper objects. In the case of actual survey data, the measured total field will be complicated by ‘background’ magnetic anomalies generated by geological variations in the seabed and by temporal variation caused by solar activity.\u003C\u002Fp>\n\u003Ch2>Total-field Magnetic Gradiometers\u003C\u002Fh2>\n\u003Cp>A total-field gradiometer is a specialised type of magnetometer that measures a first spatial derivative, or gradient of the total magnetic field. The simplest gradiometer consists of two sensors separated by a fixed distance that simultaneously measure the total magnetic field. Difference in intensity is divided by distance between the sensors, giving a linear estimate of the gradient.The orientation of the axis between the sensors determines which independent component of the three-dimensional field is measured (x, y, or vertical). A well-designed gradiometer is not affected by diurnal variation (solar effects) and tends to suppress longer wavelength geological anomalies that may interfere in target mapping applications.\u003C\u002Fp>\n\u003Cp>For decades, two-sensor gradiometers that measure a single axis of the magnetic gradient have been used. These measure a directional quantity that is dependent on their orientation in space, which frequently makes their data more, not less, complicated to interpret than total-field data.They tend to enhance magnetic structures orientated in specific directions.This is an undesirable characteristic for small-object survey.\u003C\u002Fp>\n\u003Cp>For example, Figure 2c shows the calculated east-west magnetic gradient over the same objects calculated for the total field map in Figure 2b. Smaller and shallower targets are more easily resolved than in the total field map. However, due to the nature of horizontal gradient data, it is difficult to pinpoint the source locations. Furthermore, horizontal gradient data is still prone to anomaly distortions related to permanent magnetisation.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_1390\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2018-01-16-at-8.47.49-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1390\" class=\"wp-image-1390\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2018-01-16-at-8.47.49-AM.png\" alt=\"\" width=\"500\" height=\"425\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1390\" class=\"wp-caption-text\">Figure 2: Modelled target map. a- Schematic of target sizes and locations. b- Total field map. c-Single axis gradient in east-west direction. d- Analytic signal. Colour intensity units are nT for (b) or nT\u002Fm for (c) and (d)\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>Three-axis Gradient – the Analytic Signal\u003C\u002Fh2>\n\u003Cp>Clearly, the magnetic gradient is a vector quantity in itself – despite the fact that it is derived from scalar (non-directional) values. The simple gradiometers described above measure only one axis of the total gradient vector at a time.To measure the entire vector, we need to measure gradient along three independent directions in 3D space.This is precisely the task for which the SeaQuest gradiometer was designed.\u003C\u002Fp>\n\u003Cp>Once we have the entire gradient vector, we can calculate its magnitude – ignoring its direction for the moment, just as we do with total magnetic field.The result is known as the analytic signal: a data form that is used in geophysical investigations to highlight specific types of geological features. Like the single-axis gradients, the analytic signal is a higher-frequency data form than the total field. That is, it is able to resolve small targets near to each other with greater precision than total field. But, unlike the single-axis gradients, analytic signal is a completely non-directional quantity and is unaffected by the measuring platform’s orientation in space.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_709\" style=\"width: 510px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.20.32-PM.png\" rel=\"attachment wp-att-709\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-709\" class=\"wp-image-709\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.20.32-PM.png\" alt=\"Screen Shot 2015-10-29 at 4.20.32 PM\" width=\"500\" height=\"185\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-709\" class=\"wp-caption-text\">Figure 3: Analytic signal of the same object and field inclinations as in Figure 1. Vertical units are nT\u002Fm\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>This characteristic makes interpretation of the analytic signal very easy and intuitive. Looking back to the 10kg object we modelled in Figure 1, Figure 3 shows the same object modelled in analytic signal form at the same three Earth field inclinations. The analytic signal produces a clean, positive peak that is centred directly over the source of each target. The shape of the peak is largely unaffected by the Earth’s field inclination and also therefore by the ratio of permanent and induced magnetisation in the target.\u003C\u002Fp>\n\u003Cp>In our modelled target field, Figure 2d shows the same objects as in 2a,b and c in analytic signal form.A clear peak marks each target. Most importantly, some small targets that were obscured in the total field by the presence of nearby large sources are now clearly visible.This last characteristic is in fact one of the most valuable features of using analytic signal. The most difficult complication in a successful small-target survey is frequently elimination of sources of geological interference. Geology typically manifests itself as large, distant anomalies that can exceed the amplitudes of the small targets by orders of magnitude in the total field.As a higher frequency data form, the analytic signal is very effective at suppressing strong, distant sources of interference while enhancing the small, nearby sources we are interested in for target search.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_711\" style=\"width: 310px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.24.14-PM.png\" rel=\"attachment wp-att-711\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-711\" class=\"wp-image-711\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-10-29-at-4.24.14-PM.png\" alt=\"Screen Shot 2015-10-29 at 4.24.14 PM\" width=\"300\" height=\"411\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-711\" class=\"wp-caption-text\">Figure 4: Field example data. a- total magnetic field map. Targets are obscured by deeper geological sources. b- Analytic signal map of same area created by gridding raw SeaQuest data. Interpreted target positions indicated by triangle symbols. Smaller targets indicated by cross-symbols\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>Field Example\u003C\u002Fh2>\n\u003Cp>In June 2003 a Marine Magnetics SeaQuest gradiometer was used by the US Naval Underwater Warfare Center to conduct a high-resolution survey in the inshore waters near their Keyport,Washington facility. The goal was to map the area’s man-made magnetic debris. Figure 4a shows the total magnetic field data collected by the top sensor of the gradiometer. This image represents data that would be obtainable by a conventional marine total field survey and is presented for comparison purposes. The image is dominated by sweeping anomalies related to geological variations of the seabed. This strong background magnetic response makes it difficult to quickly identify anomalies associated with ferrous objects, especially in the eastern half of the survey block. Only four potential ferrous targets in the western half of the survey site are readily identifiable (arrows).\u003C\u002Fp>\n\u003Cp>The recorded analytic signal data is displayed in Figure 4b. The geological features are effectively suppressed.As a result, at least twelve targets are readily identifiable (triangle symbols). The interpretation of the target positions is also simplified, since all targets are expressed as ‘bulls-eye’ type positive anomalies. The most prominent feature of the analytic signal data is the large anomaly just east of the centre of the analytic signal map. Despite its large size, the anomaly is obscured by geology in the total field data. Dive teams later verified this target as a buried car.\u003C\u002Fp>\n\u003Ch2>Summary\u003C\u002Fh2>\n\u003Cp>Analytic signal is a data-form that provides superior resolution of small ferrous objects. As a higher frequency data form than total magnetic field, the analytic signal tends to enhance the effects of small nearby targets and suppress the effects of large distant sources, such as geology.This has the effect of lowering the apparent environmental ‘noise’ level in the data, allowing smaller, fainter targets to be resolved.\u003C\u002Fp>\n\u003Cp>Analytic signal is also a simple, nondirectional quantity that identifies the location of targets with a clear peak. This makes an analytic signal map intuitive and easy to interpret – the closest thing possible to a magnetic image of the seafloor. This characteristic also makes it easy to identify targets with an automated algorithm. Marine Magnetics’ SeaQuest gradiometer is designed to directly measure the analytic signal by simultaneously measuring three magnetic gradient axes. The result is a magnetic surveying tool that provides a new standard for high-resolution small-target search.\u003C\u002Fp>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F10\u002Fhigh-res-magnetic-target-survey.pdf\">Download the Full Report\u003C\u002Fa>\u003C\u002Fdiv>\n",{"rendered":1481,"protected":21},"\u003Cp>Magnetic surveying is a common methodology for small-object detection applications such as UXO clearance, pipeline location and archaeology. Now gradiometers using Overhauser technology are doing the job faster and better by directly measuring the analytic signal – a high-resolution data form that is ideal for resolving small magnetic features and eliminating the unwanted effects of […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[610,713,332],[1486,15,36,37,38,39,335,615,716,336],"post-36",{"external_link":28,"hero_media":1488,"credits":1516,"related_products":1517},{"width":340,"height":341,"file":1489,"filesize":1490,"sizes":1491,"image_meta":1512,"id":1514,"url":1515},"2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey.png",1391787,{"medium":1492,"large":1496,"thumbnail":1500,"medium_large":1504,"chip":1508},{"file":1493,"width":50,"height":347,"mime-type":183,"filesize":1494,"url":1495},"High-Resolution-Magnetic-Target-Survey-300x200.png",107054,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey-300x200.png",{"file":1497,"width":57,"height":352,"mime-type":183,"filesize":1498,"url":1499},"High-Resolution-Magnetic-Target-Survey-1024x683.png",826767,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey-1024x683.png",{"file":1501,"width":63,"height":63,"mime-type":183,"filesize":1502,"url":1503},"High-Resolution-Magnetic-Target-Survey-150x150.png",43711,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey-150x150.png",{"file":1505,"width":68,"height":361,"mime-type":183,"filesize":1506,"url":1507},"High-Resolution-Magnetic-Target-Survey-768x512.png",519113,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey-768x512.png",{"file":1509,"width":86,"height":86,"mime-type":183,"filesize":1510,"url":1511},"High-Resolution-Magnetic-Target-Survey-100x100.png",21357,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1513},[],823,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FHigh-Resolution-Magnetic-Target-Survey.png","\u003Cp>Written by Doug Hrvoic and Matthew Pozza, Marine Magnetics Corporation.\u003C\u002Fp>\n",[542],{"self":1519,"collection":1524,"about":1526,"author":1528,"replies":1530,"version-history":1533,"predecessor-version":1536,"acf:post":1540,"wp:attachment":1542,"wp:term":1545,"curies":1550},[1520],{"href":1521,"targetHints":1522},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F36",{"allow":1523},[111],[1525],{"href":114},[1527],{"href":117},[1529],{"embeddable":120,"href":121},[1531],{"embeddable":120,"href":1532},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=36",[1534],{"count":608,"href":1535},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F36\u002Frevisions",[1537],{"id":1538,"href":1539},824,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F36\u002Frevisions\u002F824",[1541],{"embeddable":120,"href":579},[1543],{"href":1544},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=36",[1546,1548],{"taxonomy":143,"embeddable":120,"href":1547},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=36",{"taxonomy":146,"embeddable":120,"href":1549},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=36",[1551],{"name":150,"href":151,"templated":120},{"id":1553,"date":1554,"date_gmt":1555,"guid":1556,"modified":1558,"modified_gmt":1559,"slug":1560,"status":14,"type":15,"link":1561,"title":1562,"content":1564,"excerpt":1566,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1568,"categories":1569,"application":1570,"class_list":1572,"acf":1575,"_links":1616},46,"2007-01-01T14:58:54","2007-01-01T19:58:54",{"rendered":1557},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=46","2026-05-24T23:17:09","2026-05-25T03:17:09","seaspy-overhauser-magnetometer-technical-application-guide","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2007\u002F01\u002F01\u002Fseaspy-overhauser-magnetometer-technical-application-guide\u002F",{"rendered":1563},"SeaSPY Overhauser Magnetometer Technical Application Guide",{"rendered":1565,"protected":21},"\u003Cp>This paper provides a thorough description of what a SeaSPY Overhauser magnetometer is, what it does, and how it does it. In doing so, it references advanced concepts in the fields of electromagnetics, quantum physics, and mathematics. However, it does not assume that its audience has a technical background, and its arguments are placed in language that anyone can understand.\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Cstrong>Section 1\u003C\u002Fstrong> provides an introduction to the principles of magnetism. It describes how magnetic fields are modeled, and defines the terms necessary to understand the model. It also describes how different materials interact with magnetic fields, and how to detect objects using those interactions.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Section 2\u003C\u002Fstrong> introduces the Earth’s magnetic field, and gives an introduction to methods used to measure it.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Section 3\u003C\u002Fstrong> provides a thorough technical description of how a SeaSPY Overhauser magnetometer works.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Section 4\u003C\u002Fstrong> describes common terms and concepts that are used in magnetometry, and how they relate to the SeaSPY magnetometer.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Ch2>Section 1: Modeling and Using Magnetic Fields\u003C\u002Fh2>\n\u003Ch3>\u003Cstrong>Vectors and Fields\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The term vector refers to a quantity whose value may be represented by both a magnitude and a direction in space. Force, velocity, and acceleration are all examples of vectors.\u003C\u002Fp>\n\u003Cp>A field may be defined mathematically as some function of a vector within a region of space, so that a vector quantity is defined at every point in the region. The field that is most familiar to us all is the gravitational force field generated by the Earth. We know this field exists because we can feel it all the time – our bodies have sensors that tell us it is all around us, wherever we go over the surface of the Earth.\u003C\u002Fp>\n\u003Cp>Another field that is constantly present all around us is the Earth’s magnetic field. Although our bodies do not have sensors that allow us to detect this field directly, people have long had tools that can detect it and map it. A compass needle, for example, will have a force exerted upon it by a surrounding magnetic field; it is a tool that is designed to measure only the directional component of the magnetic field vector at its location.\u003C\u002Fp>\n\u003Cp>In order to visualize a field that we cannot directly see, it is often necessary to make a map of the field, in the same way we map the Earth’s geography. One-dimensional maps chart the value of the field as it changes over a line of space. Two-dimensional maps are charts of the field over an area of space. A common model for a two-dimensional map is the contour map, which shows lines where the local vector is constant. The lines are spaced apart by the resolution of the map.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>The Nature of Magnetic Fields\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The symbol for magnetic field intensity is H, and its units are amperes per meter (A\u002Fm). Magnetic flux is a concept that has been invented to help visualize magnetic fields, and to help understand the way they interact. A magnetic contour map of the space around a bar magnet, for example, will show contour lines SeaSPY Technical Application Guide rev1.4 Page 2 of 13 Copyright 2007 Marine Magnetics Corp flowing around the magnet. These lines are known as magnetic flux lines, and the concentration of lines within an area of space is known as magnetic flux density.\u003C\u002Fp>\n\u003Cp>The symbol for magnetic flux density is B, and the unit for it is the Tesla (T). An older unit that is often used for magnetic flux density is the gauss (G), where 1T is the same as 10,000 G. A gamma is a non-SI unit that is sometimes used by geophysicists. One gamma is equal to 1nT (10-9 T).\u003C\u002Fp>\n\u003Cp>In free space, (i.e. a vacuum devoid of matter) a magnetic field produces magnetic flux according to the following relation.\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.32.22-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-789 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.32.22-PM.png\" alt=\"\" width=\"175\" height=\"52\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where µo is defined as the permeability of free space, and has a value of 4π x 10-7 henrys per meter (H\u002Fm). The presence of different materials in a magnetic field will alter the distribution of magnetic flux because they have a magnetic permeability that is different from that of free space. This is discussed further in a later section.\u003C\u002Fp>\n\u003Cp>Gauss’ law states that magnetic flux must ‘flow’ in closed loops; flux lines do not terminate on a ‘magnetic charge’. A consequence of this law is that all magnetic fields must exist in the form of dipoles. Every source of magnetic field must have a positive (north) and negative (south) pole. By convention, magnetic flux flows from the source object’s north pole to its south pole outside the object. The magnetic flux returns from the south to the north pole within the object, closing the loop.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Magnetic permeability of materials\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>When a material is placed in a magnetic field, the magnetic flux density produced in the material is expressed as\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.32.58-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-791 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.32.58-PM.png\" alt=\"\" width=\"201\" height=\"66\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where µr is the relative magnetic permeability of the material. Materials for which µr is less than one are called diamagnetic, since they seem to ‘oppose’ the applied magnetic field. Materials for which µr is greater than one seem to ‘amplify’ the applied field, and are called paramagnetic. Some materials have very high permeability, and these are known as ferromagnetic. All materials that are thought of as being ‘magnetic’ fall in this category.\u003C\u002Fp>\n\u003Cp>If the flux density of a vacuum is subtracted from the flux density of a material, the result is a quantity that represents the added flux density due only to the material. This difference can be expressed as µoI where I is the induced magnetization of the material – the magnetic field created by the interaction of the applied field with the material’s magnetic permeability. The total flux density within the material can therefore be expressed as:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.33.37-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-792 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.33.37-PM.png\" alt=\"\" width=\"256\" height=\"85\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>The value I \u002F H is defined as the magnetic susceptibility of the material. Mathematically, this is equal to µr – 1, and it is has no units. Diamagnetic materials will have a negative susceptibility, and paramagnetic materials will have a positive susceptibility. Free space has a susceptibility of 0.\u003C\u002Fp>\n\u003Cp>Although susceptibility is unitless, its values differ depending on the system used to quantify magnetic field. This paper will specify susceptibilities in the SI system of units. The cgs system is also commonly used in geology and geophysics. To convert the SI units for susceptibility to cgs, divide by 4π.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Permanent Magnetization\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The above section describes the formation of an induced dipole when a magnetic field is applied to a material. When a large magnetic field is applied to a ferromagnetic material and then removed, the material will retain the magnetization that was induced by the high field. This magnetization is known as a permanent dipole. In order to demagnetize a material that has a permanent dipole, a field of opposing direction must be applied to the material. The value of the field that is necessary to demagnetize the material is known as the coercive force, Hc, and is a physical property of the material.\u003C\u002Fp>\n\u003Cp>Materials that have a relatively large Hc are known as magnetically hard. Those with a relatively small Hc are known as magnetically soft. This property is not related to the physical hardness of the material.\u003C\u002Fp>\n\u003Cp>A ferromagnetic material may also be magnetized (or demagnetized) by heating it above its Curie temperature – by definition the temperature above which the material is no longer paramagnetic. If such a material is cooled in the presence of a magnetic field, it will retain most of the magnetization induced by this field. The permanent magnetization of geological minerals is a result of cooling in the presence of the Earth’s magnetic field.\u003C\u002Fp>\n\u003Cp>As a result of this latter effect, most man-made ferromagnetic objects have a permanent magnetization that was introduced when the object was formed. The permanent dipole can be removed from an object by the process of degaussing. Military vehicles are often degaussed by passing them through a suite of magnetometer sensors that can determine the amount of permanent magnetization in the vehicle, and then by applying strong cancellation fields to eliminate the magnetization.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Magnetic Moment \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The concepts of induced and permanent magnetization are not enough to model an object’s total magnetic influence. Magnetic moment is a measure of the total strength of a dipole. Technically, it is defined as the torque experienced when a dipole is at right angles to a magnetic field of unit intensity1 . It is a function of the object’s size and shape as well as its magnetic properties.\u003C\u002Fp>\n\u003Cp>Conceptually, magnetic moment is the integral of the object’s magnetization over its volume. It is also a function of the length of the dipole (the distance between the north and south poles). In order to simplify the calculation of magnetic moment, it is convenient to assume a point-source dipole. This is actually quite accurate if the model need only represent the object’s magnetic influence at distances much farther from the object than the object’s size. In this case, an object’s magnetic moment, M, can be represented by the following relation:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.33.55-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-793 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.33.55-PM.png\" alt=\"\" width=\"157\" height=\"102\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where \u003Cstrong>B\u003C\u002Fstrong>i is the material’s internal flux density, and V is the material’s volume. M has units of A·m2 . An object’s permanent and induced dipoles will geometrically add to form a single dipole that produces \u003Cstrong>B\u003C\u002Fstrong>i.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Detecting magnetic objects \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Once an object’s magnetic moment is known, one can calculate the intensity of the object’s magnetic influence at varying distances. Conversely, one can use data gathered by a magnetometer to pinpoint the size and location of a magnetic moment of unknown origin. 1 Handbook of Chemistry and Physics 67th ed. CRC Press, 1986. Page F-91. SeaSPY Technical Application Guide rev1.4 Page 4 of 13 Copyright 2007 Marine Magnetics Corp Since the calculative tools described so far by this paper assume that the magnetic moment is generated by a point source, we have as yet no means of using magnetometer data to determine the actual size of an object (i.e. its mass or volume). However, by making a few reasonable assumptions, we can estimate a ferromagnetic object’s size and mass from the size of its magnetic moment.\u003C\u002Fp>\n\u003Cp>First, it is very complicated to model the influence of a permanent dipole moment, since it can have any orientation within the Earth’s ambient field, and there is rarely any means to estimate its magnitude. It is therefore convenient to assume a worst-case scenario of no permanent magnetization of the object. Second, the object’s average magnetic susceptibility can usually be estimated with a little bit of information about the material that makes up most of the object. Many man-made structures, especially relatively modern ones, are made of iron-based alloys. For the purposes of this section, we will assume that the object being searched for is made of low-grade, high-carbon iron with a susceptibility of 100. Further information on the susceptibility of iron alloys is available in the next section.\u003C\u002Fp>\n\u003Cp>Second, the object’s average magnetic susceptibility can usually be estimated with a little bit of information about the material that makes up most of the object. Many man-made structures, especially relatively modern ones, are made of iron-based alloys. For the purposes of this section, we will assume that the object being searched for is made of low-grade, high-carbon iron with a susceptibility of 100. Further information on the susceptibility of iron alloys is available in the next section.\u003C\u002Fp>\n\u003Cp>Our final estimation is that the magnetic influence of a dipole moment is spherical in shape around the dipole’s source. Although this is not precisely true, the amount of error introduced by this estimation will be less than our estimation of the object’s overall susceptibility.\u003C\u002Fp>\n\u003Cp>The magnetic influence of a magnetic object can be deduced directly from the object’s dipole moment using the following relation2 :\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.34.28-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-794 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.34.28-PM.png\" alt=\"\" width=\"159\" height=\"91\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where Br is the flux density induced by the object at distance r. Using our solution for magnetic moment above, this relation can be expressed as:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.34.49-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-795 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.34.49-PM.png\" alt=\"\" width=\"170\" height=\"94\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>The final question that remains is: how can we calculate Bi, the material’s internal flux density? If we go back to the discussion about magnetic permeability of materials, we find that magnetic susceptibility is used to represent the added flux density within a permeable material, over and above that of free space. Bi can be determined by multiplying the material’s susceptibility by the value of the ambient flux density (the intensity of the Earth’s magnetic field at the given location. See the Earth’s Magnetic Field section).\u003C\u002Fp>\n\u003Cp>Using the equations given above, we now have the tools we need to estimate the magnetic influence of various sized iron objects at varying distances. The following chart shows the influences of iron objects of different masses, using a density of 7.86g\u002Fcm3 . The chart is a log-log plot, which shows the third-order relations as straight lines.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_796\" style=\"width: 850px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.35.17-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-796\" class=\"wp-image-796 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.35.17-PM.png\" alt=\"\" width=\"840\" height=\"634\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-796\" class=\"wp-caption-text\">This chart has been calculated assuming no permanent magnetization of the object, a susceptibility of 100, and an ambient field of 50,000nT.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>To conclude this section, it must be acknowledged that the above may seem like a lot of approximations. An exacting scientist would have reason to be wary. The assumptions taken here may cause these calculations to be valid only to within an order of magnitude. However, many pieces of information are often not available to the magnetic searcher. Even a coarse approximation such as that offered here is frequently enough to design parameters for a magnetic survey that will be successful in pinpointing the locations of the objects being searched for.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>A note about steels and iron alloys \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>High purity laboratory-grade iron can have a susceptibility of up to 100,0003 . Alloying elements such as chromium, and impurities such as carbon decrease the susceptibility. In general, high carbon steel and cast iron, although still very magnetic, are less magnetically permeable than low-carbon steels.\u003C\u002Fp>\n\u003Cp>Certain types of stainless steel consist of the nonmagnetic austenitic microstructure (an example is marine-grade alloy 316). These steels are rarely used for structural or vehicular applications due to high cost. Welding, machining and cold work of austenitic stainless steel can cause a reversion of the microstructure in the affected area to the more common martensite that is magnetic, making it very difficult to create a practical object from this material that is completely nonmagnetic.\u003C\u002Fp>\n\u003Ch2>Section 2: Measuring the Earth’s Magnetic Field\u003C\u002Fh2>\n\u003Ch3>\u003Cstrong>The Earth’s Magnetic Field \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The origin of the Earth’s magnetic field is not fully understood, but it is generally accepted that it is caused by electric current generated by movement of the Earth’s conductive, liquid iron-nickel core – a phenomenon known as the dynamo effect. As a result of this effect, the Earth resembles a large rotating permanent magnet.\u003C\u002Fp>\n\u003Cp>The magnitude of the Earth’s magnetic field varies from approximately 20,000nT at the southern Brasilian coast to over 65,000nT in northern Canada and Antarctica. The inclination (the angle between the Earth’s field and the horizontal) varies from 90o at the magnetic poles to 0o at approximately the equator.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_797\" style=\"width: 963px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.37.00-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-797\" class=\"wp-image-797 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.37.00-PM.png\" alt=\"\" width=\"953\" height=\"558\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-797\" class=\"wp-caption-text\">Map of total magnetic field intensity over the surface of the Earth, as of 1995. The contour interval is 5000nT on a Mercator projection. Source: United States Department of Defense.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch3>\u003Cstrong>Diurnal Effects\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The magnetic field produced by a single dipole has no distinct boundary; it simply decreases in intensity until it is no longer detectable. The Earth’s field, however, is within the influence of the Sun’s comparatively gigantic magnetic field. The Sun’s larger field interacts with the Earth’s, giving it a distinct boundary. The space within that boundary is known as the magnetosphere. The space outside the magnetosphere is dominated by the Sun’s field, and by a constant stream of free ions and electrons that flows from the Sun, called the solar wind.\u003C\u002Fp>\n\u003Cp>Changes in the Sun’s magnetic field affect the Earth’s field dramatically. They continually influence the position of the boundary of the magnetosphere. The Sun’s influence on the magnetosphere is apparent at SeaSPY Technical Application Guide rev1.4 Page 7 of 13 Copyright 2007 Marine Magnetics Corp the Earth’s surface as a low frequency variation that can have high amplitude. Different levels of solar activity can result in changes of several hundred nT in the course of a few hours.\u003C\u002Fp>\n\u003Cp>A base station magnetometer (such as Marine Magnetics’ SENTINEL product) is a unit whose sole purpose is to measure diurnal variations, for subsequent correction of mobile survey data. This is a similar concept to using a GPS reference station to correct mobile GPS data. Placing a base station reasonably close to a survey area (within 50-100km) can completely eliminate diurnal effects. Alternately, if increased distance and lower temporal resolution can be tolerated, worldwide magnetic observatory data can be obtained over the Internet from Intermagnet4 .\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Total Field and Vector Magnetometers \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Regardless if the source of the anomaly created by a ferromagnetic object is a permanent or induced dipole, or a combination of both, the intensity of the anomaly will always be small when compared with the Earth’s relatively strong ambient magnetic field. When the field of the anomaly is vector-added to the surrounding Earth’s field, the change in the directional component of the Earth’s field will be insignificant. The change in the magnitude of the Earth’s field vector will be far more significant.\u003C\u002Fp>\n\u003Cp>Total field magnetometers (like SeaSPY) measure only the magnitude of the magnetic field vector, independent of its direction with respect to the sensor. Vector magnetometers have the ability to measure the component of ambient magnetic field that is projected along one dimension in space. Flux gates, Magnetoresistive, and Hall-Effect sensors are all examples of vector magnetometers.\u003C\u002Fp>\n\u003Cp>In order to calculate the total field, three separate vector magnetometer sensors must be oriented at right angles to each other, and their outputs geometrically added by a signal processor. There are practical limitations to how precisely and how rigidly the three sensors can be fixed together at exactly right angles. For this reason, the total-field precision of even the best flux-gate magnetometers is limited to an order of magnitude less than a SeaSPY magnetometer. Furthermore, the output of all vector-field sensors will experience drift with time and with temperature. Vector magnetometers require periodic calibration with an accurate reference such as a proton-spin magnetometer. Proton-spin magnetometers never require calibration, even when first manufactured.\u003C\u002Fp>\n\u003Cp>This is why total-field magnetometers are inherently superior to vector magnetometers when the task is detection of ferromagnetic anomalies within the Earth’s magnetosphere, especially for long-term monitoring applications. It is also the reason why total field magnetometers are so widely used in the fields of oceanography, geophysical exploration, and buried object detection.\u003C\u002Fp>\n\u003Ch2>Section 3: SeaSPY Theory of Operation\u003C\u002Fh2>\n\u003Cp>Marine Magnetics’ SeaSPY product measures the ambient magnetic field using a specialized branch of Nuclear Magnetic Resonance technology, applied specifically to hydrogen nuclei (protons).\u003C\u002Fp>\n\u003Cp>SeaSPY is not what is commonly known as a ‘proton magnetometer’; it is an Overhauser magnetometer. Although still relying on proton spin resonance, an Overhauser magnetometer is as different from a proton magnetometer as a gasoline engine is from a steam engine. Both devices are based on similar physics, but they perform their task completely differently, and this is apparent in their relative levels of performance.\u003C\u002Fp>\n\u003Cp>As with steam and gasoline engines, it is important to understand the way a proton magnetometer sensor works before attempting to understand the more sophisticated Overhauser sensor.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Proton-spin magnetometers \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>A standard proton-spin magnetometer sensor begins with a small volume of proton-rich fluid such as kerosene or methanol. Inducing a large temporary artificial magnetic field around the liquid (usually with a coil) will cause the spin populations of the protons in the liquid to become biased toward one state, effectively aligning the spin axes of a small majority of protons5 . This is known as polarization. In effect, this process endows the liquid with an induced magnetic moment, since the liquid as a whole behaves as a paramagnetic (or in the case of water, a diamagnetic) material.\u003C\u002Fp>\n\u003Cp>When fully polarized (i.e. when the external field has been applied for a long enough time), the proton spin population will follow the following relation:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.39.18-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-798 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.39.18-PM.png\" alt=\"\" width=\"181\" height=\"98\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where N+ and N- are the number of protons with positive and negative spin polarizations respectively, Bp is the ambient (applied) magnetic flux density, and k is Boltzmann’s constant (1.381×10-23 J\u002FK). µi here is the magnetic moment of a proton (1.41×10-26 A·m2 ) – it should not be confused with magnetic permeability.\u003C\u002Fp>\n\u003Cp>The larger the ratio of N+ to N-, the larger the overall magnetization of the liquid, and the more signal the magnetometer will be able to produce.\u003C\u002Fp>\n\u003Cp>The importance of this relation is that the maximum output signal of a proton magnetometer is proportional to the applied field, Bp. To generate a practical level of signal, Bp must be very large (usually more than 100 times the magnitude of the Earth’s field). This requires a great deal of energy to maintain long enough for polarization to occur.\u003C\u002Fp>\n\u003Cp>Once the proton population has been polarized, the proton spin axes are stimulated to precess around the ambient magnetic field vector. This process is known as deflection, since it deflects the proton spin axes from their equilibrium direction with the application of a sharp magnetic pulse. This is analogous to nudging the axis of a spinning top so that it begins to precess around the vertical gravity force vector as it spins.\u003C\u002Fp>\n\u003Cp>The alternating magnetic field generated by proton precession may be detected by a coil, and its frequency measured by the magnetometer electronics. This frequency is directly proportional to the magnitude of the ambient field vector.\u003C\u002Fp>\n\u003Cp>In practice, the process of polarization and signal measurement are alternated to sample the ambient magnetic field. The proton precession signal cannot be sampled while the polarizing field is in place.\u003C\u002Fp>\n\u003Cp>The proton precession frequency will occupy a single narrow spectral line, whose width depends on the chemistry of the solvent. Furthermore, this frequency is completely independent of environmental effects such as temperature. This gives proton-spin total-field magnetometers unsurpassed accuracy and stability characteristics.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>The Overhauser Effect\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The difference between proton and Overhauser magnetometers is most apparent in the way that the proton spin populations are biased. The Overhauser effect is a phenomenon that uses electron-proton coupling to achieve proton polarization.\u003C\u002Fp>\n\u003Cp>A specially engineered chemical that contains a free radical atom6 (an atom with an unbound electron) is added to the proton-rich liquid. The unbound electrons in the fluid can be easily and efficiently stimulated by exposure to low-frequency RF radiation that corresponds to a specific energy level transition. Instead of re-releasing this energy as emitted radiation, the unbound electrons transfer it to nearby protons. This polarizes the protons without the need to generate a large artificial magnetic field.\u003C\u002Fp>\n\u003Cp>When polarized, the proton spin population in an Overhauser magnetometer will follow this relation:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.40.04-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-799 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.40.04-PM.png\" alt=\"\" width=\"242\" height=\"97\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where h is Plank’s constant (6.626×10-34 J·s), ωi is the proton spin angular frequency, and ωs is the electron spin angular frequency. ωi is a function of the ambient field, and ωs is heavily dependent on the molecular structure of the Overhauser chemical.\u003C\u002Fp>\n\u003Cp>The significance of this relation is that the maximum output signal of an Overhauser magnetometer will depend on the design of the Overhauser chemical, not on the amount of energy that is put into the sensor. Consequently, SeaSPY Overhauser magnetometer sensors can produce clear and strong proton precession signals using only 1-2W of power. In contrast, standard proton sensors cannot produce signals that approach the same order of magnitude, even when consuming hundreds of Watts of power.\u003C\u002Fp>\n\u003Cp>Another benefit of the Overhauser effect is that polarization power is applied at a frequency that is far out of the bandwidth of the precession signal. Therefore, the sensor can be polarized in tandem with precession signal measurement. This effectively doubles the amount of information available to the magnetometer, allowing faster sampling rates than standard proton magnetometers.\u003C\u002Fp>\n\u003Cp>Since Overhauser magnetometers measure the same proton-resonance spectral line as standard proton magnetometers, they exhibit the same excellent accuracy and long-term stability characteristics. Added to this are larger bandwidth, lower power consumption, and sensitivity that is one to two orders of magnitude better.\u003C\u002Fp>\n\u003Ch2>Section 4: Characteristics of SeaSPY Magnetometers\u003C\u002Fh2>\n\u003Cp>Magnetometers, like most sensory instruments, consist of two basic parts: a sensor and a measurement device. The sensor produces an analog electrical signal that is proportional to the external influence being sensed, in this case magnetic field. Magnetometer sensors are active sensors, meaning they require external energy to function. The minimum amount of energy required for the magnetometer sensor to do its job is limited by the physics of the magnetometer technology.\u003C\u002Fp>\n\u003Cp>The measurement device converts the analog signal produced by the sensor into digital magnetic field units. The measurement device is also frequently responsible for real-time control of the sensor, ensuring that the sensor receives the correct amount of power, or is stimulated properly at the right time.\u003C\u002Fp>\n\u003Cp>All total-field magnetometer sensors produce a signal whose frequency is proportional to magnetic field. The measurement device is therefore in essence a very precise frequency counter.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Resolution \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Resolution is a characteristic of the measurement device. It is the minimum change in signal frequency that the measurement device can resolve. In a properly designed device, resolution is reflected by the number of significant digits that are displayed.\u003C\u002Fp>\n\u003Cp>SeaSPY’s resolution is 0.001nT, meaning that if an ideal noise-free magnetometer signal were being measured, variations as small as 0.001nT would be detected.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Sensitivity \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Sensitivity is a measure of how small a variation in actual magnetic field can be detected by the instrument as a whole. In a properly designed magnetometer, sensitivity is a characteristic of the sensor, and is a direct function of the base noise level of the sensor signal.\u003C\u002Fp>\n\u003Cp>The simplest method of calculating noise level is to assume that the noise within a set of data is broadband (white) noise, i.e. noise that is truly random. If this assumption is true, the root-mean-squared (RMS) model may be applied. The RMS value of a sample of data of n points is represented by the symbol σ. It is calculated as follows:\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.40.34-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-800 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.40.34-PM.png\" alt=\"\" width=\"204\" height=\"110\" \u002F>\u003C\u002Fa>\u003C\u002Fp>\n\u003Cp>Where m is the mean of the data sample, xi is each data point (from 1 to n), and Σ is the summation operator. σ is also known as the standard deviation of the sample. The units for σ are the same as xi. Therefore the σ of a sample of magnetometer data is represented in nT.\u003C\u002Fp>\n\u003Cp>A more accurate method of specifying the noise level of a data set is to divide the noise power in the data by its frequency bandwidth – that is, the entire range of frequencies that the data can possibly represent. The result is called the noise spectral density of the data, and it is represented in units of nT\u002F √Hz.\u003C\u002Fp>\n\u003Cp>The maximum frequency that can be represented by a set of data is one-half the sampling rate, known as the Nyquist frequency. For example, the Nyquist frequency of data sampled at 1Hz is 0.5Hz.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Bandwidth \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Bandwidth is defined as the range of frequencies of magnetic field variation that can be detected by the magnetometer. SeaSPY’s bandwidth is its Nyquist frequency. Therefore, to calculate the noise spectral density of SeaSPY data sampled at 1Hz, the RMS value of the data sample should be divided by the SeaSPY Technical Application Guide rev1.4 Page 11 of 13 Copyright 2007 Marine Magnetics Corp square root of 0.5. In conditions free of external effects (such as diurnal variation) this value is consistently less than or equal to 0.015nT RMS\u002F√Hz7 .\u003C\u002Fp>\n\u003Cp>It should not be taken for granted that a magnetometer’s sampling bandwidth is its Nyquist frequency. One common method for reducing noise is by reducing the amount of high-frequency content in the magnetometer data by applying a digital low-pass filtering algorithm. This technique effectively reduces the sampling bandwidth of the magnetometer.\u003C\u002Fp>\n\u003Cp>SeaSPY magnetometers do not apply such a bandwidth-reducing filter to their data. Preserving the maximum possible sampling bandwidth presents the user with as much information as possible, allowing a digital filter to be applied later according to the user’s needs.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Drift \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Drift is the slow change of the magnetometer output with time, without an actual magnetic field change occurring. Drift can be a characteristic of either the sensor or the measuring device. Good design will reduce or even eliminate drift in the measuring device. However, drift in the sensing device usually cannot be reduced by design.\u003C\u002Fp>\n\u003Cp>Drift can be best expressed by plotting noise spectral density vs. frequency – i.e. converting the data sample from time domain to frequency domain.\u003C\u002Fp>\n\u003Cp>If a data sample is made up of only truly white noise, the frequency spectrum will be ‘flat’. That is, the data set will be made up evenly of all frequencies within the sampling bandwidth of the magnetometer. In contrast, data that exhibits drift with time will show what is known as ‘1 over f noise’, indicating that the noise level increases in the lower frequency area of the bandwidth.\u003C\u002Fp>\n\u003Cp>One of SeaSPY’s most powerful features is a complete lack of 1\u002Ff noise – a totally flat noise spectrum. This means that a SeaSPY magnetometer is just as sensitive at measuring magnetic field variations as slow as 0.0001 Hz as it is at measuring much faster variations. This characteristic is vital for long-term monitoring, and for creating maps of data that has been collected over long periods of time.\u003C\u002Fp>\n\u003Cp>Drift can also appear to occur due to external environmental influences. Temperature drift is the change of the output of the magnetometer as the ambient temperature increases or decreases. A SeaSPY magnetometer will show less than 0.01nT temperature drift over its entire specified temperature range of –40C to +60C. This is because an Overhauser sensor shows no temperature drift, and the SeaSPY electronics measure the sensor frequency using a time reference with extremely high temperature stability.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Heading Error \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Heading Error is a change in the magnetometer’s output that is due to a change in the direction of magnetic field with respect to the magnetometer sensor. There are two possible sources of this effect.\u003C\u002Fp>\n\u003Cp>The presence of an induced dipole within detection range of the sensor, and fixed to the tow system, will cause a heading error. This is because the orientation of the dipole will stay parallel to the ambient field. The dipole will therefore change direction with respect to the sensor as the ambient field changes direction with respect to the sensor. Since a dipole’s field of influence is not spherical (see footnote 2) this action will cause a change in the flux density at the sensor’s location.\u003C\u002Fp>\n\u003Cp>This source of heading error can be completely eliminated by proper design of the magnetometer as a whole. With sufficient effort, ferromagnetic material can be excluded from all structural components of the instrument. For example, the SeaSPY electronics module contains special custom-made connectors that are made without the layer of nickel that is commonly found underneath gold plating. All of the materials in the SeaSPY towfish, especially those in direct contact with the sensor, are carefully tested to have extremely low magnetic permeability, and are therefore undetectable by the sensor.\u003C\u002Fp>\n\u003Cp>The same physics that give SeaSPY Overhauser magnetometer sensors their excellent absolute accuracy characteristics also ensure that the output of these sensors will be completely independent of the ambient magnetic field direction. This is not so for all total-field magnetometers. Some optically pumped magnetometers possess an inherent heading error characteristic that is due to the physics of their operation.\u003C\u002Fp>\n\u003Cp>Heading error can be a serious problem. When creating 2-D maps, heading error will show up as an offset between successive survey lines. When searching for small anomalies, this offset can completely obscure potential targets. The heading error offset can be partially compensated for in a 2-D survey by collecting one or more tie lines of data that are perpendicular to the main survey lines. The tie lines can then be used to ‘level’ the main survey data in post-processing. However, it is always more accurate and much simpler to collect heading error-free data to begin with.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Dead Zone\u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>A dead zone is a range of rotation of a total-field magnetometer sensor, with respect to the ambient field, in which the sensor will produce no signal. When this occurs, the magnetometer will not be able to measure the value of the ambient magnetic field.\u003C\u002Fp>\n\u003Cp>Some simple proton magnetometer sensors do have a dead zone. This zone is typically a cone along the sensor’s axis that is about ±15o in size. In contrast, SeaSPY Overhauser sensors do not have a dead zone. The amount of signal produced by the sensor is completely independent of magnetic field direction.\u003C\u002Fp>\n\u003Cp>Optically pumped total-field magnetometers have a dead zone that is an inherent property of their physics of operation. Unlike an Overhauser sensor, an optically pumped sensor’s dead zone cannot be eliminated by design implementation.\u003C\u002Fp>\n\u003Cp>In some applications, a dead zone can be a tolerable shortcoming of a magnetometer. In towed marine applications, however, a dead zone can cause serious operational difficulty. It will restrict the range of headings that the magnetometer can be towed, and will often cause unacceptable complications when towing other instrumentation (such as seismic streamers or side-scan sonar) concurrently. It also makes operation in a remotely operated vehicle (ROV) or an autonomous underwater vehicle (AUV) impractical.\u003C\u002Fp>\n\u003Ch2>\u003Cstrong>Contact Information \u003C\u002Fstrong>\u003C\u002Fh2>\n\u003Cp>The purpose of this document is to answer as many questions as possible regarding Marine Magnetics’ SeaSPY magnetometer. It is a work in progress that, it is hoped, will change and grow with time. If you have any questions, suggestions, or information you would like to contribute, please \u003Ca title=\"Contact\" href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcontact\u002F\">contact us.\u003C\u002Fa>\u003C\u002Fp>\n\u003Ch2>References and Further Reading\u003C\u002Fh2>\n\u003Col id=\"footnotes\">\n\u003Cli id=\"fn1\">\u003Cstrong>Craik, Derek.\u003C\u002Fstrong> Magnetism – Principles and Applications, John Wiley and Sons, 1995.\u003Cbr \u002F>\nA complete investigation of modeling of magnetic sources of all types.\u003C\u002Fli>\n\u003Cli id=\"fn2\">\u003Cstrong>William H. Hayt.\u003C\u002Fstrong> Engineering Electromagnetics, 4th ed. McGraw-Hill, 1981.\u003Cbr \u002F>\nChapters 8 and 9 provide a thorough and complete introduction to the first principles of magnetism.\u003C\u002Fli>\n\u003Cli id=\"fn3\">Handbook of Chemistry and Physics, 67th ed. CRC Press, 1986.\u003Cbr \u002F>\nSection E119 provides a description and tables of susceptibilities of various materials. Other sections provide a good primer on magnetic properties of materials.\u003C\u002Fli>\n\u003Cli id=\"fn4\">Metals Handbook, desk edition. American Society for Metals Press, 1988.\u003Cbr \u002F>\nSection 2-19 describes first principles behind magnetization of materials. Section 20-5 provides a thorough article on materials for permanent magnets.\u003C\u002Fli>\n\u003Cli id=\"fn5\">\u003Cstrong>A.P French, Edwin Taylor.\u003C\u002Fstrong> An Introduction to Quantum Physics. M.I.T. Press, 1978.\u003Cbr \u002F>\nProvides General information on quantum states, and magnetic properties of subatomic particles. Also a good reference for physical constants.\u003C\u002Fli>\n\u003Cli id=\"fn6\">\u003Cstrong>Tom Boyd, Colorado School of Mines.\u003C\u002Fstrong> Introduction to Geophysical Exploration. http:\u002F\u002Fwww.mines.edu\u002Ffs_home\u002Ftboyd\u002FGP311\u002Fintrogp.shtml (web document). An excellent introduction to using magnetometers for geophysical survey purposes. Also describes other useful geophysical survey tools.\u003C\u002Fli>\n\u003Cli id=\"fn7\">\u003Cstrong>Albert Overhauser.\u003C\u002Fstrong> Paramagnetic relaxation in metals. Physics Review #89, 1953. pp689-700.\u003Cbr \u002F>\nIn-depth description of the electron-proton coupling phenomenon used in Overhauser sensors. Not related to magnetometry, but interesting reading for the experienced physicist.\u003C\u002Fli>\n\u003Cli id=\"fn8\">\u003Cstrong>J. T. Weaver.\u003C\u002Fstrong> Magnetic Variations Associated with Ocean Waves and Swell. Journal of Geophysical Research, vol 70 #8, 1965.\u003Cbr \u002F>\nUseful knowledge for marine surveyors operating in open water where the size of waves and swell can be significant.\u003C\u002Fli>\n\u003C\u002Fol>\n",{"rendered":1567,"protected":21},"\u003Cp>This paper provides a thorough description of what a SeaSPY Overhauser magnetometer is, what it does, and how it does it. In doing so, it references advanced concepts in the fields of electromagnetics, quantum physics, and mathematics. However, it does not assume that its audience has a technical background, and its arguments are placed in […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[610,874,611,713,1571,332],15,[1573,15,36,37,38,39,335,615,877,616,716,1574,336],"post-46","application-offshore-alt-energy",{"external_link":28,"hero_media":1576,"credits":1614,"related_products":1615},{"width":1577,"height":1578,"file":1579,"filesize":1580,"sizes":1581,"image_meta":1610,"id":1612,"url":1613},1640,1240,"2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide.png",1972595,{"medium":1582,"large":1587,"thumbnail":1592,"medium_large":1596,"1536x1536":1601,"chip":1606},{"file":1583,"width":50,"height":1584,"mime-type":183,"filesize":1585,"url":1586},"SeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-300x227.png",227,51838,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-300x227.png",{"file":1588,"width":57,"height":1589,"mime-type":183,"filesize":1590,"url":1591},"SeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-1024x774.png",774,563623,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-1024x774.png",{"file":1593,"width":63,"height":63,"mime-type":183,"filesize":1594,"url":1595},"SeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-150x150.png",20463,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-150x150.png",{"file":1597,"width":68,"height":1598,"mime-type":183,"filesize":1599,"url":1600},"SeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-768x581.png",581,319114,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-768x581.png",{"file":1602,"width":74,"height":1603,"mime-type":183,"filesize":1604,"url":1605},"SeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-1536x1161.png",1161,1182595,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-1536x1161.png",{"file":1607,"width":86,"height":86,"mime-type":183,"filesize":1608,"url":1609},"SeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-100x100.png",10645,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1611},[],680,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FSeaSPY-Overhauser-Magnetometer-Technical-Application-Guide.png","\u003Cp>Originally published in \u003Cem data-start=\"28\" data-end=\"64\">SeaSPY Technical Application Guide\u003C\u002Fem>, Rev. 1.4 (2007).\u003C\u002Fp>\n\u003Cp>Written by Doug Hrvoic, President and Co-Founder of Marine Magnetics Corporation, an electrical engineer specializing in the design of Overhauser, proton, and optically pumped quantum magnetometers since 1992.\u003C\u002Fp>\n",[543],{"self":1617,"collection":1622,"about":1624,"author":1626,"replies":1628,"version-history":1631,"predecessor-version":1635,"acf:post":1639,"wp:attachment":1641,"wp:term":1644,"curies":1649},[1618],{"href":1619,"targetHints":1620},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F46",{"allow":1621},[111],[1623],{"href":114},[1625],{"href":117},[1627],{"embeddable":120,"href":121},[1629],{"embeddable":120,"href":1630},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=46",[1632],{"count":1633,"href":1634},27,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F46\u002Frevisions",[1636],{"id":1637,"href":1638},1195,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F46\u002Frevisions\u002F1195",[1640],{"embeddable":120,"href":577},[1642],{"href":1643},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=46",[1645,1647],{"taxonomy":143,"embeddable":120,"href":1646},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=46",{"taxonomy":146,"embeddable":120,"href":1648},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=46",[1650],{"name":150,"href":151,"templated":120},{"id":1652,"date":1653,"date_gmt":1654,"guid":1655,"modified":1657,"modified_gmt":1658,"slug":1659,"status":14,"type":15,"link":1660,"title":1661,"content":1663,"excerpt":1665,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1667,"categories":1668,"application":1669,"class_list":1670,"acf":1672,"_links":1703},38,"2005-01-04T14:56:18","2005-01-04T19:56:18",{"rendered":1656},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=38","2026-05-24T23:20:39","2026-05-25T03:20:39","comparison-of-a-new-marine-magnetometer-system-to-high-resolution-aeromagnetic-data-a-case-study-from-offshore-oman","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2005\u002F01\u002F04\u002Fcomparison-of-a-new-marine-magnetometer-system-to-high-resolution-aeromagnetic-data-a-case-study-from-offshore-oman\u002F",{"rendered":1662},"Comparison of a New Marine Magnetometer System to High-Resolution Aeromagnetic Data – A Case Study From Offshore Oman",{"rendered":1664,"protected":21},"\u003Ch2>Summary\u003C\u002Fh2>\n\u003Cp>During a marine seismic survey in 1998, conducted offshore Oman for Triton Oman Inc., a marine magnetometer was used to collect a comparison a new magnetic data set for purposes of comparison with a previously flown high-resolution aeromagnetic survey. Profile analysis is provided for purposes of a critical comparison between the two data types.\u003C\u002Fp>\n\u003Ch2>Introduction\u003C\u002Fh2>\n\u003Cp>For decades, the standard for towed marine oil exploration magnetometers has been the proton precession technology. Such instruments have proven robust under demanding field conditions, but data has been subject to limitations in resolution due to a combination of measurement technology, external noise sources, and sampling limitations. The Overhauser effect sensor now available to the industry requires lower power, provides dramatically higher signal to noise, and in the configuration tested, provides RS-232 data from the towed sensor, effectively avoiding shipboard noise sources and data “line loss” associated with transmission of small analog voltages from proton precession sensors.\u003C\u002Fp>\n\u003Cp>Additional emphasis has been placed on towed marine magnetic data acquisition due to the increased safety of this method when compared to low-level aeromagnetic data acquisition.\u003C\u002Fp>\n\u003Ch2>Theory of Operation\u003C\u002Fh2>\n\u003Cp>The Overhauser effect is a phenomenon that dramatically improves the efficiency of a proton magnetometer sensor. Overhauser sensors contain a precisely engineered chemical additive that allows the sensor to be activated or polarized with tuned high frequency radiation. The result is an order of magnitude lower operating power, and one to two orders of magnitude better sensitivity over a standard proton sensor.\u003C\u002Fp>\n\u003Cp>Overhauser sensors as illustrated in this case study are also designed to deliver very high absolute accuracy, eliminating drift, heading error, and orientation problems. This characteristic is essential for creating large maps over a long period of time.\u003C\u002Fp>\n\u003Ch2>Examples from Offshore Oman\u003C\u002Fh2>\n\u003Cp>The following illustrations are from the offshore Oman case study. Figure 1 illustrates the field area of the survey, with the aeromagnetic data grid shown with an overlay of the 2D marine magnetic survey lines. Figures 2 to 5 are profile comparisons of data. Additional comparisons and vertical continuation comparisons of the data are included in the poster presentation.\u003C\u002Fp>\n\u003Cp>The area was an exceptional selection for the data comparison, since the local magnetic field contains a broad spectrum of anomaly amplitudes and wavelengths. Geologically, the Northwestern half of the area is primarily a thick carbonate section, which transitions into an ophiolite field in the Southeastern half of the survey area.\u003C\u002Fp>\n\u003Cp>Typical magnetic susceptibility values for carbonate rocks are on the order of 10-6 cgs units, with ophiolites ranging from 10-2 to 10-6 cgs units. These values may vary by an order of magnitude or more in most cases.\u003Csup id=\"fnref1\">\u003Ca href=\"#fn1\">1\u003C\u002Fa>,\u003C\u002Fsup> \u003Csup id=\"fnref2\">\u003Ca href=\"#fn2\">2\u003C\u002Fa>\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cp>\u003Cstrong>Description of data (aeromagnetic data):\u003C\u002Fstrong>\u003C\u002Fp>\n\u003Cul>\n\u003Cli>Contractor – World Geoscience Corporation\u003C\u002Fli>\n\u003Cli>Diurnally and IGRF corrected, and leveled\u003C\u002Fli>\n\u003Cli>Data every 8 meters along line\u003C\u002Fli>\n\u003Cli>Cesium vapor magnetometer sensor\u003C\u002Fli>\n\u003Cli>Cessna 404 aircraft\u003C\u002Fli>\n\u003Cli>XYZ grid 50 x 50 m, dropped onto lines for comparison\u003C\u002Fli>\n\u003Cli>Flight elevation 80 meters above mean sea level\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>\u003Cstrong>Description of data (marine data):\u003C\u002Fstrong>\u003C\u002Fp>\n\u003Cul>\n\u003Cli>Contractor – LCT\u003C\u002Fli>\n\u003Cli>Tow offset and IGRF corrected\u003C\u002Fli>\n\u003Cli>SeaSPY Overhauser effect magnetometer system\u003C\u002Fli>\n\u003Cli>Resolution 0.001 nT\u003C\u002Fli>\n\u003Cli>Sensitivity 0.015 nT\u003C\u002Fli>\n\u003Cli>Absolute accuracy 0.2 nT\u003C\u002Fli>\n\u003Cli>Approx. 70 meter seismic survey vessel\u003C\u002Fli>\n\u003Cli>Tow distance 300 meters\u003C\u002Fli>\n\u003Cli>Acquired over 19 lines during a 6 day period\u003C\u002Fli>\n\u003Cli>Data every 3 meters along line (1 Hz recording)\u003C\u002Fli>\n\u003Cli>Data not leveled or diurnally corrected\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Ch2>Airborne vs. Marine Magnetometer Comparison – Anderson, Longacre, and Quist\u003C\u002Fh2>\n\u003Cp>\u003Cstrong>General:\u003C\u002Fstrong>\u003C\u002Fp>\n\u003Cul>\n\u003Cli>The resampling of the aeromagnetic data from the final processed grid onto the same projected lines as the marine ship tracks for comparison purposes will be equivalent to the application of a small filter to the aeromagnetic data. Other than this grid to profile operation, no other filtering or operators were applied to the aeromagnetic data used for the comparison, as provided by the Operator\u003C\u002Fli>\n\u003Cli>Two different filters were applied to the marine magnetic data for best comparison with the aeromagnetic data. The initial comparisons are displayed with a 240 second filter on the marine data, and the upward continuation of the marine data was done on data with only a 60 second filter. These filters were applied in order to suppress high frequency low amplitude noise from the movement of sea waves (an electrolyte) over the marine magnetometer sensor.\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cdiv id=\"attachment_755\" style=\"width: 539px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.27.20-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-755\" class=\"wp-image-755 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.27.20-PM.png\" alt=\"\" width=\"529\" height=\"337\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-755\" class=\"wp-caption-text\">Figure 1: Area of the case study offshore Oman, illustrating the aeromagnetic survey data coverage with an overlay showing the marine magnetometer lines. Note the varied spectral content in the magnetic data, ranging from low to high frequency and low to high amplitude magnetic anomalies.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv id=\"attachment_757\" style=\"width: 540px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.28.02-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-757\" class=\"wp-image-757 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.28.02-PM.png\" alt=\"\" width=\"530\" height=\"377\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-757\" class=\"wp-caption-text\">Figure 2: Profile comparison of aeromagnetic data profile extracted from grid (white) vs. marine data (red). A 240 second filter was applied to only the marine magnetometer data. Survey line number 32. Total horizontal scale is 50 kms, total vertical scale is 500 nT.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv id=\"attachment_758\" style=\"width: 541px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.28.43-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-758\" class=\"wp-image-758 \" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.28.43-PM.png\" alt=\"\" width=\"531\" height=\"378\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-758\" class=\"wp-caption-text\">Figure 3: Zoom in profile comparison of aeromagnetic data profile extracted from grid (white) vs. marine magnetic data (red). A 240 second filter was applied to only the marine magnetometer data. Survey line number 32. Total horizontal scale is 15 kms, total vertical scale is 500 nT.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv id=\"attachment_1386\" style=\"width: 541px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2018-01-16-at-8.18.59-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1386\" class=\"wp-image-1386\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2018-01-16-at-8.18.59-AM.png\" width=\"531\" height=\"376\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1386\" class=\"wp-caption-text\">Figure 4: Profile comparison of aeromagnetic data profile extracted from grid (white) vs. marine magnetic data (red). A 60 second filter was applied to only the marine magnetometer data, which has been upward continued 80 meters for comparison purposes. Survey line number 32. Total horizontal scale is 15 kms, total vertical scale is 500 nT.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv id=\"attachment_1385\" style=\"width: 541px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2018-01-16-at-8.19.11-AM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1385\" class=\"wp-image-1385\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2018-01-16-at-8.19.11-AM.png\" width=\"531\" height=\"374\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-1385\" class=\"wp-caption-text\">Figure 5: Zoom in profile comparison of aeromagnetic data profile extracted from grid (white) vs. marine magnetic data (red). A 60 second filter was applied to only the marine magnetometer data, which has been upward continued 80 meters for comparison purposes. Survey line number 32. Total horizontal scale is 15 kms, total vertical scale is 500 nT.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>Conclusions\u003C\u002Fh2>\n\u003Cp>This case study illustrates the field performance of the Overhauser effect marine magnetometer system in a real exploration ennvironment.  Subsequent field studies have shown similar system performance in other areas of the world.\u003C\u002Fp>\n\u003Cp>In comparison with vintage marine magnetometer data, the Overhauser system is providing an order of magnitude higher resolution marine magnetic data than the industry has consistently achieved with other technologies.  These improvements, in parallel with lowered risk to data acquisition personnel, provide significant advances in the state of the art for marine magnetic mapping.\u003C\u002Fp>\n\u003Ch2>Acknowledgements\u003C\u002Fh2>\n\u003Cp>The authors would like to thankfully acknowledge The Management of Triton Oman, Inc. and the Oman Ministry of Oil and Gas for their providing access to the data presented.\u003C\u002Fp>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002Fcomparison-new-marine.pdf\">Download Original Report\u003C\u002Fa>\u003C\u002Fdiv>\n\u003Ch2>References\u003C\u002Fh2>\n\u003Col id=\"footnotes\">\n\u003Cli id=\"fn1\">\u003Cstrong>S. Breiner\u003C\u002Fstrong>, Applications Manual for Portable Magnetometers, Geometrics Publication, 1973. \u003Ca class=\"backlink\" href=\"#fnref1\">↩︎\u003C\u002Fa>\u003C\u002Fli>\n\u003Cli id=\"fn2\">\u003Cstrong>L. Nettleton. \u003C\u002Fstrong> \u003Ca class=\"backlink\" href=\"#fnref2\">↩︎\u003C\u002Fa>\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Brown, R.P., Comeaux, L.B., and Ward, R.W.\u003C\u002Fstrong>, Submitting an Expanded Abstract Using sSubmit, Society of Exploration Geophysicists International Exposition and 68th Annual Meeting, New Orleans 1998.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Ross, C.P. and Verm, R.W.\u003C\u002Fstrong>, Submitting an Expanded Abstract Using Submit with EASE, Society of Exploration Geophysicists International Exposition and 69th Annual Meeting, Houston 1999.\u003C\u002Fli>\n\u003C\u002Fol>\n",{"rendered":1666,"protected":21},"\u003Cp>Summary During a marine seismic survey in 1998, conducted offshore Oman for Triton Oman Inc., a marine magnetometer was used to collect a comparison a new magnetic data set for purposes of comparison with a previously flown high-resolution aeromagnetic survey. Profile analysis is provided for purposes of a critical comparison between the two data types. […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[713],[1671,15,36,37,38,39,335,716],"post-38",{"external_link":28,"hero_media":1673,"credits":1701,"related_products":1702},{"width":340,"height":341,"file":1674,"filesize":1675,"sizes":1676,"image_meta":1697,"id":1699,"url":1700},"2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman.png",650799,{"medium":1677,"large":1681,"thumbnail":1685,"medium_large":1689,"chip":1693},{"file":1678,"width":50,"height":347,"mime-type":183,"filesize":1679,"url":1680},"Comparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-300x200.png",57642,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-300x200.png",{"file":1682,"width":57,"height":352,"mime-type":183,"filesize":1683,"url":1684},"Comparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-1024x683.png",412286,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-1024x683.png",{"file":1686,"width":63,"height":63,"mime-type":183,"filesize":1687,"url":1688},"Comparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-150x150.png",23020,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-150x150.png",{"file":1690,"width":68,"height":361,"mime-type":183,"filesize":1691,"url":1692},"Comparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-768x512.png",263689,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-768x512.png",{"file":1694,"width":86,"height":86,"mime-type":183,"filesize":1695,"url":1696},"Comparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-100x100.png",11397,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1698},[],831,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F12\u002FComparison-of-a-New-Marine-Magnetometer-System-to-High-Resolution-Aeromagnetic-Data-–-A-Case-Study-From-Offshore-Oman.png","\u003Cp data-start=\"91\" data-end=\"346\">Written by Brian S. Anderson (Fugro-LCT), Mark B. Longacre (MBL, Inc.), and Patrick Quist (Fugro-LCT).\u003C\u002Fp>\n",[543],{"self":1704,"collection":1709,"about":1711,"author":1713,"replies":1715,"version-history":1718,"predecessor-version":1721,"acf:post":1725,"wp:attachment":1727,"wp:term":1730,"curies":1735},[1705],{"href":1706,"targetHints":1707},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F38",{"allow":1708},[111],[1710],{"href":114},[1712],{"href":117},[1714],{"embeddable":120,"href":121},[1716],{"embeddable":120,"href":1717},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=38",[1719],{"count":874,"href":1720},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F38\u002Frevisions",[1722],{"id":1723,"href":1724},1199,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F38\u002Frevisions\u002F1199",[1726],{"embeddable":120,"href":577},[1728],{"href":1729},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=38",[1731,1733],{"taxonomy":143,"embeddable":120,"href":1732},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=38",{"taxonomy":146,"embeddable":120,"href":1734},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=38",[1736],{"name":150,"href":151,"templated":120},{"id":1738,"date":1739,"date_gmt":1740,"guid":1741,"modified":1743,"modified_gmt":1744,"slug":1745,"status":14,"type":15,"link":1746,"title":1747,"content":1749,"excerpt":1751,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1753,"categories":1754,"application":1755,"class_list":1756,"acf":1758,"_links":1789},42,"2004-03-16T14:57:46","2004-03-16T19:57:46",{"rendered":1742},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=42","2026-01-26T12:27:36","2026-01-26T17:27:36","marine-magnetic-survey-of-a-submerged-roman-harbour-caesarea-maritima-israel","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2004\u002F03\u002F16\u002Fmarine-magnetic-survey-of-a-submerged-roman-harbour-caesarea-maritima-israel\u002F",{"rendered":1748},"Marine Magnetic Survey of a Submerged Roman Harbour, Caesarea Maritima, Israel",{"rendered":1750,"protected":21},"\u003Ch2>Abstract\u003C\u002Fh2>\n\u003Cp>The harbour built by King Herod’s engineers at Caesarea represented a major advance in Roman harbour construction that incorporated the use of large (390 m3 ), form-filled hydraulic concrete blocks to build an extensive foundation for the harbour moles and breakwater barriers. Marine geophysical surveys were recently conducted across the submerged harbour in an attempt to map the configuration of the buried concrete foundation. A total of 107 line km of high-resolution marine magnetic surveys (nominal 15 m line separations) and bathymetry were acquired over a 1 km2 area of the submerged harbour using an Overhauser marine magnetometer, integrated DGPS and single-beam (200 KHz) echosounder. The feasibility of magnetic detection of the concrete was established before the survey by magnetic susceptibility testing of concrete core samples. All concrete samples contained appreciable amounts of fe-oxide-rich volcanic ash (‘pozzolana’) and showed uniformly high susceptibility values (κ > 10-4 cgs) when compared to harbour bottom sediments and building stones (κ < 10-6 cgs).\u003C\u002Fp>\n\u003Cp>Magnetic surveys identify a localized increase in magnetic intensity (ca. 3-10 nT) that is attributed to the presence of hydraulic concrete within the buried harbour structure. The mapped anomaly patterns are distinctly rectilinear, indicating that the concrete foundation was laid out in ‘header’ fashion in dominantly N-S and W-E trending segments. Magnetic lows identify ‘cells’ within the concrete framework that were likely backfilled with harbour sediments prior to construction of the harbour moles and quays.\u003C\u002Fp>\n\u003Ch2>Summary\u003C\u002Fh2>\n\u003Cp>This study demonstrates the utility of magnetic methods for mapping buried concrete structures in a marine archaeological setting and provides important new insights into the method of construction of Herod’s harbour. Magnetic property testing of hydraulic concrete samples shows that they are characterised by high magnetic susceptibilities and are good targets for magnetic detection. It is anticipated that the methods described here will have wider application to other Roman harbour sites where pozzolan concrete materials were employed.\u003C\u002Fp>\n\u003Cp>Magnetic mapping at Sebastos confirms that concrete structures exposed at several locations on the harbour are part of a much more extensive foundation work that underlies the entire mole structure (Fig. 8B). The interpreted magnetic anomaly patterns suggest that the two moles were established by the construction of two large rectangular ‘islets’ with concrete perimeter walls and internal compartments or ‘cells’. The compartments were either actively infilled, or acted as large baffles trapping littoral sediment through the natural processes of longshore drift.\u003C\u002Fp>\n",{"rendered":1752,"protected":21},"\u003Cp>Abstract The harbour built by King Herod’s engineers at Caesarea represented a major advance in Roman harbour construction that incorporated the use of large (390 m3 ), form-filled hydraulic concrete blocks to build an extensive foundation for the harbour moles and breakwater barriers. Marine geophysical surveys were recently conducted across the submerged harbour in an […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[610,713],[1757,15,36,37,38,39,335,615,716],"post-42",{"external_link":28,"hero_media":1759,"credits":1787,"related_products":1788},{"width":340,"height":341,"file":1760,"filesize":1761,"sizes":1762,"image_meta":1783,"id":1785,"url":1786},"2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel.png",2409156,{"medium":1763,"large":1767,"thumbnail":1771,"medium_large":1775,"chip":1779},{"file":1764,"width":50,"height":347,"mime-type":183,"filesize":1765,"url":1766},"Marine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-300x200.png",138795,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-300x200.png",{"file":1768,"width":57,"height":352,"mime-type":183,"filesize":1769,"url":1770},"Marine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-1024x683.png",1648471,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-1024x683.png",{"file":1772,"width":63,"height":63,"mime-type":183,"filesize":1773,"url":1774},"Marine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-150x150.png",52226,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-150x150.png",{"file":1776,"width":68,"height":361,"mime-type":183,"filesize":1777,"url":1778},"Marine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-768x512.png",942294,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-768x512.png",{"file":1780,"width":86,"height":86,"mime-type":183,"filesize":1781,"url":1782},"Marine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-100x100.png",23375,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1784},[],820,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMarine-Magnetic-Survey-of-a-Submerged-Roman-Harbour-Caesarea-Maritima-Israel.png","\u003Cp>Originally published in \u003Ca href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetic-Survey-Nautical-Archaeology.pdf\">The International Journal of Nautical Archaeology, Volume 33, Issue 1\u003C\u002Fa> (2004).\u003Cbr data-start=\"191\" data-end=\"194\" \u002F>Written by Joseph I. Boyce, Eduard G. Reinhardt, Avner Raban, and Matthew R. Pozza.\u003C\u002Fp>\n",[1343,543],{"self":1790,"collection":1795,"about":1797,"author":1799,"replies":1801,"version-history":1804,"predecessor-version":1808,"acf:post":1812,"wp:attachment":1815,"wp:term":1818,"curies":1823},[1791],{"href":1792,"targetHints":1793},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F42",{"allow":1794},[111],[1796],{"href":114},[1798],{"href":117},[1800],{"embeddable":120,"href":121},[1802],{"embeddable":120,"href":1803},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=42",[1805],{"count":1806,"href":1807},10,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F42\u002Frevisions",[1809],{"id":1810,"href":1811},821,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F42\u002Frevisions\u002F821",[1813,1814],{"embeddable":120,"href":577},{"embeddable":120,"href":1368},[1816],{"href":1817},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=42",[1819,1821],{"taxonomy":143,"embeddable":120,"href":1820},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=42",{"taxonomy":146,"embeddable":120,"href":1822},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=42",[1824],{"name":150,"href":151,"templated":120},{"id":1826,"date":1827,"date_gmt":1828,"guid":1829,"modified":1831,"modified_gmt":1832,"slug":1833,"status":14,"type":15,"link":1834,"title":1835,"content":1837,"excerpt":1839,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1840,"categories":1841,"application":1842,"class_list":1843,"acf":1845,"_links":1876},34,"2003-01-01T14:52:29","2003-01-01T19:52:29",{"rendered":1830},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=34","2026-01-26T12:57:13","2026-01-26T17:57:13","magnetic-mapping-of-buried-hydraulic-concrete-harbour-structures-king-herods-harbour-caesarea-maritima-israel","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2003\u002F01\u002F01\u002Fmagnetic-mapping-of-buried-hydraulic-concrete-harbour-structures-king-herods-harbour-caesarea-maritima-israel\u002F",{"rendered":1836},"Magnetic Mapping of Buried Hydraulic Concrete Harbour Structures: King Herod’s Harbour, Caesarea Maritima, Israel",{"rendered":1838,"protected":21},"\u003Ch2>Abstract\u003C\u002Fh2>\n\u003Cp>The harbour built by King Herod’s engineers at Caesarea represented a major advance in Roman harbour construction that incorporated the use of large (390 m3 ), form-filled hydraulic concrete blocks to build an extensive foundation for the harbour moles and breakwater barriers. Marine geophysical surveys were recently conducted across the submerged harbour in an attempt to map the configuration of the buried concrete foundation. A total of 107 line km of high-resolution marine magnetic surveys (nominal 15 m line separations) and bathymetry were acquired over a 1 km2 area of the submerged harbour using an Overhauser marine magnetometer, integrated DGPS and single-beam (200 KHz) echosounder. The feasibility of magnetic detection of the concrete was established before the survey by magnetic susceptibility testing of concrete core samples. All concrete samples contained appreciable amounts of fe-oxide-rich volcanic ash (‘pozzolana’) and showed uniformly high susceptibility values (κ > 10-4 cgs) when compared to harbour bottom sediments and building stones (κ < 10-6 cgs).\u003C\u002Fp>\n\u003Cp>Magnetic surveys identify a localized increase in magnetic intensity (ca. 3-10 nT) that is attributed to the presence of hydraulic concrete within the buried harbour structure. The mapped anomaly patterns are distinctly rectilinear, indicating that the concrete foundation was laid out in ‘header’ fashion in dominantly N-S and W-E trending segments. Magnetic lows identify ‘cells’ within the concrete framework that were likely backfilled with harbour sediments prior to construction of the harbour moles and quays.\u003Csup id=\"fnref1\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Ch2>Introduction\u003C\u002Fh2>\n\u003Cp>The harbour built by King Herod’s engineers at Caesarea Maritima (Fig 1a) represented a major advance in Roman harbour construction. The marine structure incorporated the use of large (390 m3 ), form-filled hydraulic concrete blocks to build an extensive foundation for the harbour moles and breakwater barriers. The now ruined harbour covers a 10 Ha area (Fig. 1b) and lies submerged at depths of 3-9 m below present sea level.\u003Csup id=\"fnref2\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cp>Underwater excavations conducted at the harbour site during the last two decades have revealed a wealth of information about Roman harbour engineering and technology \u003Csup id=\"fnref5\"> \u003C\u002Fsup>(Holfelder, 1988, 1997, 1999; Hillard, 1989; Oleson, 1988; Raban,1992, 1994, Raban et al. 1999). What set this harbour apart from other Roman harbours of its time was the innovative use of hydraulic concrete (a mixture of lime, volcanic ash and aggregate) to construct an extensive breakwater barrier and foundation for the harbour moles (Fig. 1b). The importance of hydraulic concrete in the construction of the harbour is well established but the extent and the detailed layout of the foundation has been more difficult to reconstruct. The foundation is well exposed at several locations on the breakwater perimeter (Fig. 1b), but over most of the harbour it is buried by up to 2 metres of littoral sediments and a thick rubble layer. The rubble layer consists of collapsed building stones, including large sandstone ashlars that pose a major obstacle for underwater excavations.\u003Csup id=\"fnref4\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cdiv id=\"attachment_765\" style=\"width: 462px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.50.22-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-765\" class=\"wp-image-765 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.50.22-PM.png\" alt=\"\" width=\"452\" height=\"425\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-765\" class=\"wp-caption-text\">Figure 1. a) Location of study area. b) Map of the Herodian harbour showing general location of submerged breakwaters and location of modern shoreline. Location of stratigraphic boreholes also shown (after Neev et al., 1978).\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>In 2001, a pilot project was conducted to evaluate the use of magnetic methods for mapping the layout of the buried breakwater structures. A primary objective of the geophysical work was to evaluate whether magnetic surveys could be used to detect and map the configuration of buried concrete foundation. It was reasoned that the high content of volcanic ash and tuff within the hydraulic concrete (materials rich in magnetic oxides) should provide a sufficient magnetic contrast to allow detection and mapping with a marine magnetic survey.\u003C\u002Fp>\n\u003Cp>In this paper we report on the preliminary results of magnetic property analysis of hydraulic concrete samples and marine geophysical survey work at Caesarea. This work demonstrates the utility of magnetic methods for mapping buried harbour structures and provides important new insights into the layout and method of construction of Herod’s harbour. Hydraulic concrete was used widely in the construction of other Roman ports (Brandon, 1996; Holfelder, 1997) and the methods reported here have broader application to investigations of other ancient harbour sites.\u003C\u002Fp>\n\u003Ch2>Methods\u003C\u002Fh2>\n\u003Ch3>\u003Cstrong>Magnetic property measurements \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The feasibility of detecting concrete breakwater structures with magnetic surveys was evaluated before the survey work by magnetic susceptibility testing of concrete core samples. Magnetic susceptibility is a measure of the ease with which materials obtain magnetization and can be used to estimate the strength of magnetic anomaly that will be measured during a total field magnetic survey (Pozza et al., 2002). Analyses were also conducted on a variety of harbour bottom sediments, pottery (shards) and building stones, to assess the contrasts in the magnetic susceptibility of harbour bottom materials. A total of 10 concrete core samples were tested from two locations on the southern mole (site K1 and K9). In each case 5 to10 g samples of concrete were separated from the core, dried at 40°C and then disaggregated by crushing. Each sample was then weighed and its magnetic susceptibility was determined using a Bartington MS-2 meter. A calibration sample was measured following each sample run to monitor and correct for instrument drift.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Marine geophysical surveys \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>Marine magnetic and bathymetry surveys were acquired over a 1 km2 area of the outer harbour and the adjacent offshore area over two survey days (Fig. 2). An attempt was also made to survey the modern harbour area but was abandoned due to high magnetic gradients produced by a large sunken barge at the harbour entrance. The survey was conducted from a small Zodiac inflatable boat (Fig. 3) with N-S survey lines and W-E tie lines spaced at 10-20 m intervals (total 107 line km; Fig. 2).\u003C\u002Fp>\n\u003Cp>Magnetic data were acquired using a marine Overhauser magnetometer (Marine Magnetics ‘SeaSPY’) (Fig. 3a) towed at a distance of 20 m behind the boat and a depth of 1-2 m. The sensor elevation was also recorded with each magnetic measurement to allow for later correction of the water depth related changes in magnetic intensity (‘drape corrections’ see below). The magnetometer was cycled at 4 Hz (0.25 s sample interval), providing better than one sample per meter at average boat speeds of 4 knots. The Overhauser magnetometer has the advantage of high sensitivity (0.015 nT) and does not suffer problems with heading errors and dead zones that complicate the use of optically-pumped alkali vapour magnetometers. Diurnal magnetic field variations were recorded continuously during the survey with a base station proton magnetometer located on the shoreline. Single-beam bathymetry data and positional data were acquired simultaneously with the magnetics using a 200 kHz echosounder and a differential GPS-chart plotting system.\u003C\u002Fp>\n\u003Cp>The post-cruise processing of magnetic data included de-spiking to remove ferrous anomalies, diurnal and lag corrections, tie-line levelling and micro-levelling (Minty, 1991) (to remove uncompensated diurnal and systematic errors) and application of drape corrections (Pilkington and Thurston, 2001; Pozza et al., 2002). Drape corrections remove the effects of changes in sensor altitude and bottom topography and are critical because the drop off in magnetic signal amplitude is inversely proportional to the distance to the source cubed (i.e attenuation ∝ 1\u002Fr3 ). In land-based surveys, such corrections are usually not required because the sensor(s) are carried across the ground at a relatively constant height above the ground-surface. In a marine survey, however, both the bottom topography and the elevation of the sensor are constantly changing and need to be compensated. The 1\u002Fr3 fall-off in signal (or increase in amplitude, as sensor to bottom distance decreases) may in some cases, be larger than the amplitude of the signals of interest, and may introduce a significant ‘terrain effect’ in the magnetic signal. A number of schemes have been developed for removal of terrain-induced errors and are discussed in detail elsewhere (Pilkington and Thurston, 2001).\u003C\u002Fp>\n\u003Cdiv id=\"attachment_767\" style=\"width: 384px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.58.38-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-767\" class=\"wp-image-767 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.58.38-PM.png\" alt=\"\" width=\"374\" height=\"480\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-767\" class=\"wp-caption-text\">Figure 2. Magnetic survey tracklines (total 107 line km). No data were acquired within the inner harbour area due to high magnetic gradients associated with a sunken barge at modern harbour entranceway.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>The fully corrected magnetic data were grided with a cell spacing of 3 m using a minimum curvature algorithm (Briggs, 1977) to generate the total field magnetic map shown in Fig. 5b. A regional residual separation of the total field data was performed by upward continuation to 50 m and subtraction of the regional field. Upward continuation is an analytical transform that yields the magnetic signal for some elevation above the original elevation at which the data was recorded. Subtraction of the upward continued signal has the effect of removing long wavelength signals associated with deep magnetic sources, thereby enhancing shorter wavelengths associated with shallow features of interest. The processing flow for the bathymetry data involved tie-line levelling (Markham, 2001), spline smoothing of profiles and minimum curvature griding of the data with a 3 m cell size.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_768\" style=\"width: 757px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.59.38-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-768\" class=\"wp-image-768 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.59.38-PM.png\" alt=\"\" width=\"747\" height=\"565\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-768\" class=\"wp-caption-text\">Figure 3. Zodiac inflatable boat used to collect the magnetic and bathymetric data at Caesarea. a) Marine Overhauser magnetometer (Marine Magnetics ‘ SeaSPY’), b) GPS antenna, c) Data logging computer, d) Navigation and echo sounder display.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp> \u003C\u002Fp>\n\u003Ch2>Results\u003C\u002Fh2>\n\u003Ch3>\u003Cstrong>Magnetic property analysis \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The hydraulic concrete samples show uniformly high magnetic susceptibilities, ranging from 1×10-4 to 1×10-5 c.g.s. The range of susceptibilities reflects variations in the content of volcanic ash and volcanic rock fragments (aggregate) added during the preparation of the concrete mixture. Analysis of the samples under a light microscope indicates that volcanic materials (ash and lithic fragments) make up 20-50% of the concrete by volume. The aggregate materials consist mainly of basalt and andesite fragments with varying amounts of local beach rock and sandstone bedrock.\u003C\u002Fp>\n\u003Cp>The other harbour bottom materials tested show overall lower magnetic susceptibilities when compared to the hydraulic concrete. Harbour bottom sands and muds (the most abundant bottom materials) have low susceptibilities, ranging from 1×10-5 to 5×10-7 c.g.s., while the kurkar sandstone (bedrock) has an average susceptibility of about1x10-4 c.g.s. The contrast in susceptibility between concrete and harbour bottom sediments is substantial (up to 2 orders of magnitude) and results in a magnetic anomaly that can be measured with a total field magnetic survey. Calculations performed using GM-SYS™ magnetic modeling software indicate that a 25 x 25 x 5 m block of hydraulic concrete (approximate dimensions) within harbour sediments would generate a 7 nT anomaly at a distance of 5 m (field strength 45,000 nT).\u003C\u002Fp>\n\u003Cp>Hamra sediments and pottery fragments are characterized by magnetic susceptibilities that are intermediate between the concrete and harbour bottom sediments. Some hamra samples show high susceptibility values (> 10-4 c.g.s.) owing to the high concentration of iron oxides in the paleosol layers. This suggests that hamra layers may produce significant magnetic contrasts and generate measurable magnetic anomalies.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Bathymetry \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The results of the bathymetry survey are shown as a colour-contoured shaded-relief map in Figure 4a. The water depth across the harbour area varies from approximately 2 m to over 7.5 m.\u003C\u002Fp>\n\u003Cp>The northern and southern moles and the harbour entrance channel are clearly visible in the bathymetric data and correspond well with the harbour outline previously estimated from air-photo analysis (Fig. 4. blue outline). The northern mole has a well defined rectangular structure while the southern mole has a more irregular outline and topography consisting of collapsed rubble and large ashlar blocks.\u003C\u002Fp>\n\u003Cp>The area seaward of the harbour shows a gently sloping shelf with minor erosional channels and anomalous circular feature 150 m west of the harbour (Fig.4a. CF). The feature is approximately 100 m in diameter and has a relief of ~ 0.5 m. The feature has magnetic expression as a well-defined circular anomaly (~ 3 nT) on the total field map (Figure 4b, CF). Preliminary sediment probes conducted on the feature indicate that it may represent a concentration of ballast stones or recent dredge mound. Further work is planned to determine the origin of the feature.\u003C\u002Fp>\n\u003Ch3>\u003Cstrong>Marine Magnetics \u003C\u002Fstrong>\u003C\u002Fh3>\n\u003Cp>The total magnetic field map (Fig. 4b) contains anomalies from several magnetic sources. The most prominent anomaly is a broad zone of high magnetic intensity on the eastern margin of the study area. The anomaly coincides with a sandstone (kurkar) bedrock platform which forms the modern coastline. The western edge of the platform is marked by N-S trending normal fault with a downthrown western block (Mart and Perecman, 1996). Archaeologic evidence from the site suggest that neotectonic movements on the fault may have contributed to the submergence and eventual destruction of Herod’s harbour (Raban, 1992; Reinhardt and Raban, 1999).\u003C\u002Fp>\n\u003Cdiv id=\"attachment_769\" style=\"width: 863px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.00.52-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-769\" class=\"wp-image-769 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.00.52-PM.png\" alt=\"\" width=\"853\" height=\"565\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-769\" class=\"wp-caption-text\">Figure 4. a) Shaded relief bathymetry map of harbour and shallow shelf. Irregular surface relief over breakwaters is due to thick rubble layer. SB = southern breakwater, NB = northern breakwater, HE = harbour entrance, S = scarp, CF = circular feature. Profile A-B (Figure 6) location shown. b) Total field magnetic map for same area. KP = kurkar platform, EC = erosional channels, BA = barge anomaly.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>The buried harbour is clearly defined on the total field image and the residual magnetic field map (Figure 5a) which emphasizes contributions from near-surface magnetic sources. The localized increase in magnetic intensity (ca. 3 – 10 nT) over the breakwater areas is consistent with the presence of high magnetic susceptibility hydraulic concrete within the buried harbour foundation (Raban, 1992; Reinhardt and Raban, 1999). The anomaly patterns over the breakwater areas are distinctly rectinlinear and indicate that the concrete foundation may have been constructed in a ‘header fashion’ with concrete caissons laid out in N-S and E-W trending segments. The lows between magnetic highs can be attributed to infilling of ‘cells’ within the concrete framework with low-magnetic susceptibility materials (most likely beach sand). Figure 5b shows the preliminary interpretation of the magnetic anomalies and speculated layout of the harbour foundations. The northern mole shows a distinctly ‘cellular’ pattern of anomalies, most likely because it is located in a more sheltered position and has remained relatively intact. The southern mole shows a less coherent pattern of anomalies but a roughly rectangular framework is visible at the northern end of the breakwater segment. The southern mole, in general, has undergone more extensive undermining and collapse due to wave attack and this is reflected in the magnetic response.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_771\" style=\"width: 875px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.02.55-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-771\" class=\"wp-image-771 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.02.55-PM.png\" alt=\"\" width=\"865\" height=\"573\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-771\" class=\"wp-caption-text\">Figure 5 a) Residual magnetic field map of breakwater. Note distinct rectilinear framework’ pattern of positive magnetic anomalies separated by magnetic lows defining ‘cells’ (baffles?) within breakwater structure. SB = southern breakwater; NB = northern breakwater. b) Interpretation of magnetic lineaments; linear positive magnetic anomalies are interpreted as framework of concrete foundation blocks enclosing baffles infilled with lower susceptibility sediments (sand?).\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>Other interesting magnetic anomalies in the residual field map include a circular anomaly and other linear anomalies lying in the area seaward of the Herodian breakwaters. Preliminary investigations of some of these anomalies indicate that they are associated with linear concentrations of ballast stones and other building materials. These possibly record offloading of ships ballast by merchantile vessels on their approach to the harbour. The origin of these features is under currently under investigation.\u003C\u002Fp>\n\u003Cp>Figure 6 shows magnetic and bathymetric profiles across the northern mole (location of profile shown in Figure 5a). The northern mole is indicated by double topographic peaks near the beginning of the bathymetry profile (Fig. 6a). The total magnetic field profile (Fig. 6b) clearly show double magnetic peaks directly over the mole followed by an increase in total magnetic field strength due to the buried kurkar platform. Note that the geometry of the anomalies defining the edges of the mole are repeatable and of roughly of the same width over both the southern and northern edges of the mole structure. The magnetic low between the two peaks indicates the proposed area of fill between within the concrete perimeter.\u003C\u002Fp>\n\u003Cp>Fig. 6c is the residual magnetic field profile in which the effect of the regional magnetic field has been removed. Note the relative enhancement of the anomalies defining the mole structure, indicating a near-surface origin. In this profile it is evident that the northern edge of the mole was a slightly higher amplitude (+ 2 nT) than its southern counterpart. This may indicate that the northern perimeter of was constructed with a larger volume of concrete. To north of the breakwater area, the magnetic anomaly pattern shows undulating lows and highs which are interpreted as an erosional topography cut into the sandstone platform. The bedrock channels likely record phases of lowered sea level and subaerial erosion of the coastal platform.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_772\" style=\"width: 780px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.01.42-PM-1.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-772\" class=\"wp-image-772 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-4.01.42-PM-1.png\" alt=\"\" width=\"770\" height=\"436\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-772\" class=\"wp-caption-text\">Figure 6. Magnetic and Bathymetric profiles across northern breakwater structure and Kurkar platform (Location of profile in Fig. 6a). a) Bathymetry, b) Diurnal-corrected total magnetic field, c) Residual Magnetic Field. Note twin magnetic anomalies over southern and northern edges of the breakwater structure.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Ch2>Discussion and Conclusions\u003C\u002Fh2>\n\u003Cp>This study demonstrates the utility of high-resolution marine magnetic surveying for mapping a submerged and partially buried Roman harbour. Magnetic property analysis shows that hydraulic concrete materials within the harbour are of relatively high susceptibility (> 10-5 cgs) when compared to background sediments and are suitable targets for detection with a magnetic survey. The anomaly strength of the concrete structures is small (< 7 nT) when compared to the regional field generated by the local bedrock and requires careful post-cruise processing of the magnetic data. The processing steps that were most significant were removal of diurnal variations and the lag correction. Since the targets of interest are so small (3 – 10 nT), they can be easily masked by solar diurnal variations. The application of tie-line levelling (Markham, 2001; Pozza, 2002) and micro-levelling (Minty, 1991) proved effective in removing the remaining random noise due to positional errors.\u003C\u002Fp>\n\u003Cp>High-resolution magnetic and bathymetric data were collected quickly and with minimal operational costs using a small inflatable boat, SeaSPY marine magnetometer, and integrated D-GPS\u002F echo sounder system (Fig. 4). Use of a small Zodiac inflatable enabled the close survey line spacing necessary for high resolution imaging of the harbour structure. The residual magnetic field map of the harbour clearly identifies the location of concrete footings and provides important new insights into the harbour construction. Further work is planned in the area seaward of the submerged harbour in order to better define the nature of magnetic anomalies associated with ballast stone concentrations.\u003C\u002Fp>\n\u003Cp>Hydraulic concrete was used widely in the construction of other Roman ports (Brandon, 1996; Holfelder, 1997) and the methods reported here have broader application to investigations of other ancient harbour sites.\u003C\u002Fp>\n\u003Ch2>Acknowledgements\u003C\u002Fh2>\n\u003Cp>This work was supported through the Natural Science and Engineering Research Council of Canada research grants to Boyce and Reinhardt. The authors thank S. Collins and I. Psimolous for field and laboratory assistance W.A. Morris for discussions.\u003Csup id=\"fnref6\">\u003C\u002Fsup>\u003Csup id=\"fnref5\">\u003C\u002Fsup>\u003C\u002Fp>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMaritime-Archaeology-Paper-King-Herods-Harbour.pdf\">Download the Full Report\u003C\u002Fa>\u003C\u002Fdiv>\n\u003Ch2>References\u003C\u002Fh2>\n\u003Col id=\"footnotes\">\n\u003Cli>\u003Cstrong>Boyce, J.I., Pozza, M. and Morris,\u003C\u002Fstrong> W.A., 2001. High-resolution magnetic mapping of contaminated sediments in urbanized environments. The Leading Edge, 20: 886-890.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Brandon, C.\u003C\u002Fstrong>, 1996. Cements, concrete, and settling barges at Sebastos: comparisons with other Roman harbor examples and the descriptions of Vitruvius, in Caesarea Martima: In A Retrospective After Two Millenia, edited by A. Raban and K.G. Holum, E.J. 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Exploration Geophysics, 32, p. 95-101.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Pozza, M.R., Boyce, J.I. and Morris\u003C\u002Fstrong>, W.A., 2003 Lake-based magnetic mapping of contaminated sediment distribution, Hamilton Harbour, Ontario, Canada. Journal of Applied Geophysics, In review.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Pozza, M.R.,\u003C\u002Fstrong> 2002 High-resolution marine magnetic surveying: applications to environmental and geological problems. M.Sc. Thesis, McMaster Univ, 176p.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Raban, A.\u003C\u002Fstrong>, 1992. Sebastos, the royal harbour at Caesarea Maritima – a short-lived giant. Int. J. Naut. Archaeol., 21, p. 111-124.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Raban, A.\u003C\u002Fstrong>, 1988. In search of Straton’s Tower: some additional thoughts, In R. Vann, Ed., Caesarea Papers, Thomson-Shore, Ann Arbor, p. 23-35.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Raban, A.\u003C\u002Fstrong>, 1994. Sebastos, the Herodian harbour of Caesarea: construction and operation. Sefunim, 8, 45-59.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Raban, A.\u003C\u002Fstrong>, 1991. The subsidence of Sebastos. Thracia Pontica, 4, p. 339-66.\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Raban, A., Reinhardt, E.G., McGrath, M., Hodge, N.\u003C\u002Fstrong>, 1999 The underwater excavations, 1993-94, in Caesarea Papers 2, edited by K.G. Holum, A. Raban, and J. Patrich. Journal of Roman Archaeology, Supplementary Series No. 35. Journal of Roman Archaeology: Portsmouth, RI., . p. 152-168\u003C\u002Fli>\n\u003Cli>\u003Cstrong>Reinhardt. E.G. and Raban, A.\u003C\u002Fstrong>, 1999. Destruction of Herod the Great’s harbor at Caesarea Maritima, Israel – geoarchaeological evidence. Geology, 27, p. 811-814.\u003C\u002Fli>\n\u003C\u002Fol>\n",{"rendered":1752,"protected":21},{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[610,713],[1844,15,36,37,38,39,335,615,716],"post-34",{"external_link":28,"hero_media":1846,"credits":1874,"related_products":1875},{"width":340,"height":341,"file":1847,"filesize":1848,"sizes":1849,"image_meta":1870,"id":1872,"url":1873},"2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1.png",1862799,{"medium":1850,"large":1854,"thumbnail":1858,"medium_large":1862,"chip":1866},{"file":1851,"width":50,"height":347,"mime-type":183,"filesize":1852,"url":1853},"Magnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-300x200.png",106153,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-300x200.png",{"file":1855,"width":57,"height":352,"mime-type":183,"filesize":1856,"url":1857},"Magnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-1024x683.png",1153872,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-1024x683.png",{"file":1859,"width":63,"height":63,"mime-type":183,"filesize":1860,"url":1861},"Magnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-150x150.png",41780,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-150x150.png",{"file":1863,"width":68,"height":361,"mime-type":183,"filesize":1864,"url":1865},"Magnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-768x512.png",663183,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-768x512.png",{"file":1867,"width":86,"height":86,"mime-type":183,"filesize":1868,"url":1869},"Magnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-100x100.png",19272,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1871},[],818,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F04\u002FMagnetic-Mapping-of-Buried-Hydraulic-Concrete-Harbour-Structures_-King-Herods-Harbour-Caesarea-Maritima-Israel-1.png","\u003Cdiv class=\"text-base my-auto mx-auto pb-10 [--thread-content-margin:--spacing(4)] thread-sm:[--thread-content-margin:--spacing(6)] thread-lg:[--thread-content-margin:--spacing(16)] px-(--thread-content-margin)\">\n\u003Cdiv class=\"[--thread-content-max-width:40rem] thread-lg:[--thread-content-max-width:48rem] mx-auto max-w-(--thread-content-max-width) flex-1 group\u002Fturn-messages focus-visible:outline-hidden relative flex w-full min-w-0 flex-col agent-turn\" tabindex=\"-1\">\n\u003Cdiv class=\"flex max-w-full flex-col grow\">\n\u003Cdiv class=\"min-h-8 text-message relative flex w-full flex-col items-end gap-2 text-start break-words whitespace-normal [.text-message+&]:mt-1\" dir=\"auto\" data-message-author-role=\"assistant\" data-message-id=\"ad7b96e3-fc10-4e7f-a13d-dac27fa10af1\" data-message-model-slug=\"gpt-5\">\n\u003Cdiv class=\"flex w-full flex-col gap-1 empty:hidden first:pt-[1px]\">\n\u003Cdiv class=\"markdown prose dark:prose-invert w-full break-words dark markdown-new-styling\">\n\u003Cp data-start=\"0\" data-end=\"283\" data-is-last-node=\"\" data-is-only-node=\"\">Written by J.I. Boyce and E.G. Reinhardt, School of Geography and Geology, McMaster University, Hamilton, Ontario, Canada; A. Raban, Recanati Institute of Maritime Studies, University of Haifa, Israel; and M.R. Pozza, Marine Magnetics Corporation, Richmond Hill, Ontario, Canada.\u003C\u002Fp>\n\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n\u003C\u002Fdiv>\n",[1343,543],{"self":1877,"collection":1882,"about":1884,"author":1886,"replies":1888,"version-history":1891,"predecessor-version":1894,"acf:post":1898,"wp:attachment":1901,"wp:term":1904,"curies":1909},[1878],{"href":1879,"targetHints":1880},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F34",{"allow":1881},[111],[1883],{"href":114},[1885],{"href":117},[1887],{"embeddable":120,"href":121},[1889],{"embeddable":120,"href":1890},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=34",[1892],{"count":1738,"href":1893},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F34\u002Frevisions",[1895],{"id":1896,"href":1897},819,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F34\u002Frevisions\u002F819",[1899,1900],{"embeddable":120,"href":577},{"embeddable":120,"href":1368},[1902],{"href":1903},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=34",[1905,1907],{"taxonomy":143,"embeddable":120,"href":1906},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=34",{"taxonomy":146,"embeddable":120,"href":1908},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=34",[1910],{"name":150,"href":151,"templated":120},{"id":1912,"date":1913,"date_gmt":1914,"guid":1915,"modified":1917,"modified_gmt":1918,"slug":1919,"status":14,"type":15,"link":1920,"title":1921,"content":1923,"excerpt":1925,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":1927,"categories":1928,"application":1929,"class_list":1930,"acf":1932,"_links":1963},44,"2002-01-01T14:58:22","2002-01-01T19:58:22",{"rendered":1916},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=44","2026-01-26T13:01:30","2026-01-26T18:01:30","high-resolution-magnetic-and-seismic-imaging-of-basement-faults-in-western-lake-ontario-and-lake-simcoe-canada","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2002\u002F01\u002F01\u002Fhigh-resolution-magnetic-and-seismic-imaging-of-basement-faults-in-western-lake-ontario-and-lake-simcoe-canada\u002F",{"rendered":1922},"High-resolution Magnetic And Seismic Imaging Of Basement Faults In Western Lake Ontario And Lake Simcoe, Canada",{"rendered":1924,"protected":21},"\u003Ch2>[TEST]\u003C\u002Fh2>\n\u003Ch2>Abstract\u003C\u002Fh2>\n\u003Cp>The tectonic ‘rejuvenation’ of Precambrian basement faults is now recognized as an important mechanism for generating intraplate earthquakes. In many areas of intraplate North America, concern for the design and safe operation of strategic facilities (e.g. nuclear generating stations) has prompted efforts to re-evaluate basement seismic hazards and map zones of basement faulting. In southern Ontario, Canada, recent efforts have focused on evaluating deeply seated Grenville-age (ca. 1.2 Ga) basement fault zones. The present study is applying a multi-parameter geophysical approach to investigate basement fault zones underlying several lake basins in southern Ontario. Geophysical investigations have included collection of >2000 line km of high-resolution lake-based magnetic surveys (50-100 m line spacing, 1 m in-line sampling), 5-15KHz sub-bottom sonar profiling and side-scan images in western Lake Ontario and Lake Simcoe. Results from western Lake Ontario delineate a prominent, west-east linear magnetic anomaly that is coincident with normal faulting (up to 50 m displacement) of bedrock below the buried Dundas Valley. The anomaly is aligned with surface topographic lineaments on the valley floor and the trend of a previously mapped fault with basement magnetic expression (the Hamilton-Presqu’ile fault). Magnetic mapping in western Lake Simcoe reveals west-east trending linear magnetic anomalies that displace a major Grenville-age terrane boundary. The magnetic boundaries are spatially co-incident with faulting, slumps and gas-escape structures in lake-bottom sediments and are interpreted as reactivated basement faults.\u003C\u002Fp>\n\u003Ch2>Summary\u003C\u002Fh2>\n\u003Cp>This paper has demonstrated the application of high-resolution lake-based magnetics and acoustic imaging to the study of faulting in lake basins in southern Ontario. The approach has provided important new insights into the structural characteristics of the Precambrian basement and possible linkages between basement structures and near-surface deformation.\u003C\u002Fp>\n",{"rendered":1926,"protected":21},"\u003Cp>[TEST] Abstract The tectonic ‘rejuvenation’ of Precambrian basement faults is now recognized as an important mechanism for generating intraplate earthquakes. In many areas of intraplate North America, concern for the design and safe operation of strategic facilities (e.g. nuclear generating stations) has prompted efforts to re-evaluate basement seismic hazards and map zones of basement faulting. […]\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[330],[611,713],[1931,15,36,37,38,39,335,616,716],"post-44",{"external_link":1933,"hero_media":1934,"credits":1962,"related_products":28},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMagnetic-Seismic-Imaging-of-Basement-Faults.pdf",{"width":340,"height":341,"file":1935,"filesize":1936,"sizes":1937,"image_meta":1958,"id":1960,"url":1961},"2025\u002F10\u002FBOB-6-corrections-mock.png",1219695,{"medium":1938,"large":1942,"thumbnail":1946,"medium_large":1950,"chip":1954},{"file":1939,"width":50,"height":347,"mime-type":183,"filesize":1940,"url":1941},"BOB-6-corrections-mock-300x200.png",80828,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F10\u002FBOB-6-corrections-mock-300x200.png",{"file":1943,"width":57,"height":352,"mime-type":183,"filesize":1944,"url":1945},"BOB-6-corrections-mock-1024x683.png",660998,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F10\u002FBOB-6-corrections-mock-1024x683.png",{"file":1947,"width":63,"height":63,"mime-type":183,"filesize":1948,"url":1949},"BOB-6-corrections-mock-150x150.png",33841,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F10\u002FBOB-6-corrections-mock-150x150.png",{"file":1951,"width":68,"height":361,"mime-type":183,"filesize":1952,"url":1953},"BOB-6-corrections-mock-768x512.png",401574,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F10\u002FBOB-6-corrections-mock-768x512.png",{"file":1955,"width":86,"height":86,"mime-type":183,"filesize":1956,"url":1957},"BOB-6-corrections-mock-100x100.png",17454,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F10\u002FBOB-6-corrections-mock-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":1959},[],387,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F10\u002FBOB-6-corrections-mock.png","\u003Cp>Reprinted from Proceedings of SAGEEP Annual Meeting, Feb. 2002, Las Vegas, Nevada, Environmental and Engineering Geophysical Society.\u003C\u002Fp>\n\u003Cp>Written by Joe I. Boyce, Matthew R. Pozza, and William A. Morris, (McMaster University, Hamilton, ON L8S 4K1) and Nicholas Eyles and Mike Doughty (University of Toronto at Scarborough, Scarborough, Ontario, M1C 1A4)\u003C\u002Fp>\n",{"self":1964,"collection":1969,"about":1971,"author":1973,"replies":1975,"version-history":1978,"predecessor-version":1982,"wp:attachment":1986,"wp:term":1989,"curies":1994},[1965],{"href":1966,"targetHints":1967},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F44",{"allow":1968},[111],[1970],{"href":114},[1972],{"href":117},[1974],{"embeddable":120,"href":121},[1976],{"embeddable":120,"href":1977},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=44",[1979],{"count":1980,"href":1981},21,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F44\u002Frevisions",[1983],{"id":1984,"href":1985},412,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F44\u002Frevisions\u002F412",[1987],{"href":1988},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=44",[1990,1992],{"taxonomy":143,"embeddable":120,"href":1991},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=44",{"taxonomy":146,"embeddable":120,"href":1993},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=44",[1995],{"name":150,"href":151,"templated":120},{"id":1997,"date":1998,"date_gmt":1999,"guid":2000,"modified":2002,"modified_gmt":2003,"slug":2004,"status":14,"type":15,"link":2005,"title":2006,"content":2008,"excerpt":2010,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":2012,"categories":2013,"application":2014,"class_list":2015,"acf":2017,"_links":2048},40,"2001-01-01T14:56:59","2001-01-01T19:56:59",{"rendered":2001},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=40","2026-01-26T13:00:52","2026-01-26T18:00:52","towed-body-magnetometer-enhances-subsea-surveys","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2001\u002F01\u002F01\u002Ftowed-body-magnetometer-enhances-subsea-surveys\u002F",{"rendered":2007},"Towed Body Magnetometer Enhances Subsea Surveys",{"rendered":2009,"protected":21},"\u003Cblockquote>\u003Cp>By mounting a magnetometer on a Chelsea Instruments’ NuShuttle undulating towed body, Holland ’s Rijkswaterstaat was able to locate buried wrecks that could not be pinpointed by conventional seismic techniques.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>THE WESTERSCHELDE, in the South West of the Netherlands, is the waterway connection between the Port of Antwerp and the North Sea. Broadening the channel would allow larger seagoing vessels to reach the Port of Antwerp. However, dredging of the channel could not be started because Dutch records showed a great number of shipwrecks in the Westerschelde area which would have created a hazard to the dredging works. But the exact location of the wrecks was not always recorded which led the Zeeland Division of the Rijkswaterstaat decide to identify all shipwrecks in the Westerschelde and relocate them before dredging began.\u003C\u002Fp>\n\u003Cp>The dedicated survey vessel Lodycke was equipped with various sensors, including a multibeam sonar and a Klein sidescan sonar. Accurate positioning information was obtained by RTK DGPS and PosMV heave compensation. The exact position of the sidescan towfish was determined by means of an acoustic transponder on the towfish which was tracked by the vessel’s USBL system. A l l positioning information was merged and an exact position for the different sensors was calculated by NeSA’s PDS software. Sidescan sonar data was logged and displayed using a TEI Isis sonar acquisition system.\u003C\u002Fp>\n\u003Cp>This survey spread had one drawback. It was able to locate wrecks sitting on the seabed or partly covered by sediment but did not have the capability to look beneath the seabed. Buried wrecks could not be located but these would be the biggest hazard to dredging operations. The Westerschelde is known for its diverse geology. Large quantities of heterogeneous sands make it virtually impossible to retrieve subsurface information from the area using standard sub-bottom profiling or chirp systems. Even shallow seismics proved to be unsuccessful. The use of a magnetometer appeared to be the best alternative.\u003C\u002Fp>\n\u003Cp>A magnetometer is a passive survey instrument: it does not send a signal itself, it only “listens” to signals it picks up in the water. As we are aware, the earth generates a magnetic field, which in a small enough area can be assumed to be constant. If a magnetometer is deployed in this area, the measured values will be more or less constant. However, when an object is placed inside the earth’s magnetic field, it will cause an anomaly which shows up in the data as a peak value. This is usually visible by plotting the dataset. A peak value caused by an anomaly is not always of the same shape and size – even for the same object, the magnetometer will not always produce the same anomaly size and shape.\u003C\u002Fp>\n\u003Cdiv id=\"attachment_760\" style=\"width: 461px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.40.33-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-760\" class=\"wp-image-760 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.40.33-PM.png\" alt=\"\" width=\"451\" height=\"382\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-760\" class=\"wp-caption-text\">Contour maps of magnetic anomalies yield more information than separate line graphs but can only be achieved if the height of the magneto meter can be accurately controlled – in this case by mounting it on the towed body.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>The size of this anomaly depends first of all on the material the object is made of. Metal objects will have a far greater effect on the magnetic field than, for example, those of plastic or wood. And while bigger objects can be expected to cause a bigger disturbance compared to a smaller object, the type of material, its size, shape, depth of burial and the direction of the magnetometer crossing the object have a big influence on the size and peak shape of the anomaly. Crossing an object from the opposite direction may cause the peak value to be negative instead of positive. Finally, the height of the magnetometer over the object will influence significantly the size and shape of the anomaly value. For example, a large totally buried object may produce the exact same peak value as a smaller object just below the surface. All these parameters may be a reason for not detecting an object or for misinterpreting a magnetic graph. It is therefore of the utmost importance that the survey crew has control of some if not all of these parameters. Of course it is not possible to control all parameters. The size, shape, material and depth of burial of the object cannot be controlled externally! But if the remaining parameters, such as the height of the magnetometer over the seabed can be controlled with a large degree of accuracy, estimates can be made of the object’s shape and size and maybe even the depth at which it is located.\u003C\u002Fp>\n\u003Cblockquote>\u003Cp>The SeaSpy\u002F Nu-Shuttlecombination means height is controlled to centimetric accuracy.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cp>All this sounds well in theory; how was it accomplished in the real world? As previously stated, a magnetometer detects disturbances in the earth’s magnetic field.\u003C\u002Fp>\n\u003Cp>But because most ships are made of metal the sensor will also detect this signal. So the anomaly from the survey vessel will show at a very high level, causing other anomalies to be lost in the noise. However, if the magnetometer is moved further from the vessel its influence will decrease significantly – as a rule of thumb, the survey vessel ’s influence is negligible at three times the ship’s length.\u003C\u002Fp>\n\u003Cp>\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.41.49-PM.png\">\u003Cimg loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-761 size-full\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.41.49-PM.png\" alt=\"\" width=\"465\" height=\"232\" \u002F>\u003C\u002Fa>The magnetometer selected for the job, a SeaSPY by Marine Magnetics Corporation is an Overhauser magnetometer capable of detecting very small anomalies of the earth ’s magnetic field. This is required when a sediment-covered wreck consists of several pieces of various sizes. Additionally, the Overhauser Effect enables SeaSPY to operate at very low power levels, while maintaining its high sensitivity. The unit is powered via the towcable and data is returned to the data acquisition unit, The magnetometer selected for the job, a SeaSPY by Marine Magnetics Corporation is an Overhauser magnetometer capable of detecting very small anomalies of the earth’s magnetic field. This is required when a sediment-covered wreck consists of several pieces of various sizes. Additionally, the Overhauser Effect enables SeaSPY to operate at very low power levels, while maintaining its high sensitivity. The unit is powered via the towcable and data is returned to the data acquisition unit, in this case NeSA’s PDS 1000.\u003C\u002Fp>\n\u003Cp>The PDS software logs the magnetometer data into a file for later charting. Graphs of the data can also be made using PDS software. Unfortunately, graphs of separate lines alone do not give sufficient information on anomalies. More information can be retrieved from contour maps, where several lines are combined to produce a contour plot, but this is only possible if the height of the magnetometer can be accurately controlled. Furthermore the towfish position has to be known. In consequence, what was needed was a stabilised, controllable platform. After appraising a number of vehicles, NeSA and Rijkswaterstaat chose the Chelsea Instrument Nn-Shuttle.\u003C\u002Fp>\n\u003Cp>By fitting the SeaSPY magnetometer to the Nn-Shuttle, its height can be controlled to centimetric accuracy by using the PDS 1000 software. Together with the USBL transponder mounted on the Nn-Shuttle, this resulted in a magnetometer that was controllable and from which highly accurate positioning information could be acquired.\u003C\u002Fp>\n\u003Cp>Using this specialised wreck finding tool, the Lodycke survey crew was able to locate all the wrecks. After clearance they re-surveyed the area using the magnetometer to confirm the salvage team had completed this work. This way a final check was made to make sure all parts of the wrecks were removed properly.\u003C\u002Fp>\n\u003Cp>The combination of the Chelsea Instruments Nn-Shuttle and the Marine Magnetics SeaSPY magnetometer was so successful that shortly afterwards another Rijkswaterstaat division decided to invest in the same combination of Nn-Shuttle and magnetometer. They intend to use the system for wreck surveys in the North Sea. After successfully using the SeaSPY\u002FNnShuttle combination, the Zeeland Division of Rijkswaterstaat expanded the system with a second SeaSPY magnetometer, creating a stable, highly controllable transverse gradiometer for even more precise measurements. The Chelsea Nn-Shuttle and the Marine Magnetics’ SeaSPY magnetometer have proven to be a useful tool in wreck detection surveys and made it possible to not only check the seabed surface but also below for wreck debris.\u003C\u002Fp>\n\u003Cp>Chelsea Instruments’ Nn-Shuttle towed undulating vehicle was developed in cooperation with Plymouth Marine Laboratory under the DTI’s Support for Products Under Research (SPUR) scheme. There are now over 25 Nn-Shuttles operating worldwide.\u003C\u002Fp>\n\u003Cp>Among Nn-Shuttle attributes are that it is capable of undulating deeper than any other towed vehicle of its type with or without faired cable. It also offers a highly responsive and easily controllable undulating system and it is this attribute that was utilised by NeSA.\u003C\u002Fp>\n\u003Cp>The full range of Chelsea’s towed undulating vehicles (from large carriers capable of undulating down to 500 metres, to vehicles designed for deployment from smaller towing vessels and ships of opportunity) include SeaSoar MkII, ScanFish MkI & MkII, AQUAshuttle andNn-Shuttle.\u003C\u002Fp>\n\u003Cp> \u003C\u002Fp>\n\u003Cdiv id=\"attachment_762\" style=\"width: 241px\" class=\"wp-caption aligncenter\">\u003Ca href=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.43.01-PM.png\" rel=\"attachment wp-att-762\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-762\" class=\"size-full wp-image-762\" src=\"http:\u002F\u002Fwww.marinemagnetics.com\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FScreen-Shot-2015-11-16-at-3.43.01-PM.png\" alt=\"Nu-Shuttle with USBL transponder on its port bow and magnetometer underneath.\" width=\"231\" height=\"164\" \u002F>\u003C\u002Fa>\u003Cp id=\"caption-attachment-762\" class=\"wp-caption-text\">Nu-Shuttle with USBL transponder on its port bow and magnetometer underneath.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cdiv>\u003Ca class=\"button medium\" href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FTowed-Body-Magnetics.pdf\">Download Original Article\u003C\u002Fa>\u003C\u002Fdiv>\n",{"rendered":2011,"protected":21},"\u003Cp>The SeaSpy\u002FNu-Shuttle combination means height is controlled to centimetric accuracy.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[610,713,332],[2016,15,36,37,38,39,614,615,716,336],"post-40",{"external_link":28,"hero_media":2018,"credits":2046,"related_products":2047},{"width":340,"height":341,"file":2019,"filesize":2020,"sizes":2021,"image_meta":2042,"id":2044,"url":2045},"2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys.png",1714146,{"medium":2022,"large":2026,"thumbnail":2030,"medium_large":2034,"chip":2038},{"file":2023,"width":50,"height":347,"mime-type":183,"filesize":2024,"url":2025},"Towed-Body-Magnetometer-Enhances-Subsea-Surveys-300x200.png",106909,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys-300x200.png",{"file":2027,"width":57,"height":352,"mime-type":183,"filesize":2028,"url":2029},"Towed-Body-Magnetometer-Enhances-Subsea-Surveys-1024x683.png",1040961,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys-1024x683.png",{"file":2031,"width":63,"height":63,"mime-type":183,"filesize":2032,"url":2033},"Towed-Body-Magnetometer-Enhances-Subsea-Surveys-150x150.png",40955,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys-150x150.png",{"file":2035,"width":68,"height":361,"mime-type":183,"filesize":2036,"url":2037},"Towed-Body-Magnetometer-Enhances-Subsea-Surveys-768x512.png",610618,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys-768x512.png",{"file":2039,"width":86,"height":86,"mime-type":183,"filesize":2040,"url":2041},"Towed-Body-Magnetometer-Enhances-Subsea-Surveys-100x100.png",19683,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":2043},[],682,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FTowed-Body-Magnetometer-Enhances-Subsea-Surveys.png","\u003Cp>Written by Natasja Verboom (NeSA B.V., Holland), Malcolm Morgan, and Justin Dunning (Chelsea Instruments Ltd, UK).\u003C\u002Fp>\n",[1343,543],{"self":2049,"collection":2054,"about":2056,"author":2058,"replies":2060,"version-history":2063,"predecessor-version":2066,"acf:post":2069,"wp:attachment":2072,"wp:term":2075,"curies":2080},[2050],{"href":2051,"targetHints":2052},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F40",{"allow":2053},[111],[2055],{"href":114},[2057],{"href":117},[2059],{"embeddable":120,"href":121},[2061],{"embeddable":120,"href":2062},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=40",[2064],{"count":608,"href":2065},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F40\u002Frevisions",[2067],{"id":352,"href":2068},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F40\u002Frevisions\u002F683",[2070,2071],{"embeddable":120,"href":577},{"embeddable":120,"href":1368},[2073],{"href":2074},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=40",[2076,2078],{"taxonomy":143,"embeddable":120,"href":2077},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=40",{"taxonomy":146,"embeddable":120,"href":2079},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=40",[2081],{"name":150,"href":151,"templated":120},{"id":2083,"date":2084,"date_gmt":2085,"guid":2086,"modified":2088,"modified_gmt":2089,"slug":2090,"status":14,"type":15,"link":2091,"title":2092,"content":2094,"excerpt":2096,"author":24,"featured_media":25,"comment_status":26,"ping_status":27,"sticky":21,"template":28,"format":29,"meta":2098,"categories":2099,"application":2100,"class_list":2101,"acf":2103,"_links":2137},567,"2000-03-01T12:12:23","2000-03-01T17:12:23",{"rendered":2087},"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002F?p=567","2026-01-26T12:25:17","2026-01-26T17:25:17","marine-magnetometer-said-to-minimise-seismic-interference-risk-2","https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002F2000\u002F03\u002F01\u002Fmarine-magnetometer-said-to-minimise-seismic-interference-risk-2\u002F",{"rendered":2093},"Marine Magnetometer Said To Minimise Seismic Interference Risk",{"rendered":2095,"protected":21},"\u003Ch1>Marine magnetometer said to minimise seismic interference risk.\u003C\u002Fh1>\n\u003Cp>Fugro-LCT is claiming a significant breakthrough in the acquisition of marine magnetic data with its GUNMAG\u003Csup id=\"fnref1\">\u003C\u002Fsup> marine magnetometer system\u003Csup id=\"fnref2\">\u003C\u002Fsup>.\u003C\u002Fp>\n\u003Cp>The company \u003Csup id=\"fnref3\">\u003C\u002Fsup>says that magnetic surveys are most economically conducted in conjunction with seismic acquisition, and for some time now this has posed the problem for potential interference with the seismic equipment. The small risk of entanglement of 250m magnetometer cable with streamers or guns is often seen by seismic contractors as unjustifiable, given the overall cost of the survey. As a result, magnetic data has often not been acquired in areas where it would enhance the geological interpretation.\u003C\u002Fp>\n\u003Cp>Fugro-LCT’s GUNMAG system utilises the SeaSPY Overhauser-effect magnetometer which has several technical advantages over the proton precession magnetometers routinely used in marine acquisition. The SeaSPY is said to increase sampling, typically 1 Hz. With much improved sensitivity and accuracy.\u003C\u002Fp>\n\u003Cp>Most importantly, the company says that the SeaSpy magnetometer signal is digitized to the onboard recording system. The signal therefore suffers no degradation in transmission, in contrast to the analogue voltages produced by proton precession magnetometers. When deployed in conventional, towed sensor mode, the SeaSPY tow cable is only half the diameter of conventional tow cables saving on the need for a dedicated winch.\u003C\u002Fp>\n\u003Cblockquote>\u003Cp>Fugro-LCT has recently designed and engineered a tow block to allow the SeaSPY to be towed from the seismic gun array. The magnetometer links into the existing conductor bundle to the gun array for data transmission and needs only a short 50m tow cable to maintain sufficient distance from the guns. The sensor is kept at the same depth as the guns and well clear of the seismic cables and other equipment.\u003C\u002Fp>\u003C\u002Fblockquote>\n\u003Cdiv id=\"attachment_470\" style=\"width: 310px\" class=\"wp-caption aligncenter\">\u003Cimg loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-470\" class=\"wp-image-470 size-medium\" src=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FGradientMap-300x191.png\" alt=\"\" width=\"300\" height=\"191\" srcset=\"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FGradientMap-300x191.png 300w, https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FGradientMap-768x489.png 768w, https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2015\u002F04\u002FGradientMap.png 940w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \u002F>\u003Cp id=\"caption-attachment-470\" class=\"wp-caption-text\">The presented results demonstrate the inherent advantages of measuring all three components of the magnetic gradient vector and interpreting total gradient data when attempting to quickly locate the position and depth of ferro-metallic objects. The total gradient data allowed easy identification of several targets in the survey area that otherwise would have been missed by conventional survey methods due to geologically sourced magnetic anomalies.\u003C\u002Fp>\u003C\u002Fdiv>\n\u003Cp>The simplicity of installation, according to the company, means that the system can be linked into any of the gun arrays and multiple sensors can be towed to ensure data redundancy or provide magnetic gradient information. The GUNMAG system has already been deployed on a two-month survey off shore Brazil and further surveys are planned.\u003C\u002Fp>\n",{"rendered":2097,"protected":21},"\u003Cp>Fugro-LCT’s GUNMAG system uses the SeaSPY magnetometer to capture precise magnetic data alongside seismic surveys—without the usual interference risks.\u003C\u002Fp>\n",{"_acf_changed":21,"inline_featured_image":21,"footnotes":28},[608],[713],[2102,15,36,37,38,39,614,716],"post-567",{"external_link":28,"hero_media":2104,"credits":2135,"related_products":2136},{"width":1577,"height":1578,"file":2105,"filesize":2106,"sizes":2107,"image_meta":2132,"id":58,"url":2134},"2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk.png",3136424,{"medium":2108,"large":2112,"thumbnail":2116,"medium_large":2120,"1536x1536":2124,"chip":2128},{"file":2109,"width":50,"height":1584,"mime-type":183,"filesize":2110,"url":2111},"Marine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-300x227.png",105256,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-300x227.png",{"file":2113,"width":57,"height":1589,"mime-type":183,"filesize":2114,"url":2115},"Marine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-1024x774.png",1057648,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-1024x774.png",{"file":2117,"width":63,"height":63,"mime-type":183,"filesize":2118,"url":2119},"Marine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-150x150.png",38119,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-150x150.png",{"file":2121,"width":68,"height":1598,"mime-type":183,"filesize":2122,"url":2123},"Marine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-768x581.png",609273,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-768x581.png",{"file":2125,"width":74,"height":1603,"mime-type":183,"filesize":2126,"url":2127},"Marine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-1536x1161.png",2276786,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-1536x1161.png",{"file":2129,"width":86,"height":86,"mime-type":183,"filesize":2130,"url":2131},"Marine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-100x100.png",18470,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk-100x100.png",{"aperture":210,"credit":28,"camera":28,"caption":28,"created_timestamp":210,"copyright":28,"focal_length":210,"iso":210,"shutter_speed":210,"title":28,"orientation":210,"keywords":2133},[],"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMarine-Magnetometer-Said-To-Minimise-Seismic-Interference-Risk.png","\u003Cp>Originally published in \u003Ca href=\"https:\u002F\u002Fdev2.hypelabs.dev\u002Fmarine\u002Fcms\u002Fcustom\u002Fuploads\u002F2025\u002F11\u002FMinimise-Seismic-Risk.pdf\">First Break, Volume 18, Issue 3\u003C\u002Fa> (March 2000). Written by Fugro LCT.\u003C\u002Fp>\n",[1343,543],{"self":2138,"collection":2143,"about":2145,"author":2147,"replies":2149,"version-history":2152,"predecessor-version":2155,"acf:post":2159,"wp:attachment":2162,"wp:term":2165,"curies":2170},[2139],{"href":2140,"targetHints":2141},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F567",{"allow":2142},[111],[2144],{"href":114},[2146],{"href":117},[2148],{"embeddable":120,"href":121},[2150],{"embeddable":120,"href":2151},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcomments?post=567",[2153],{"count":330,"href":2154},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F567\u002Frevisions",[2156],{"id":2157,"href":2158},673,"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fposts\u002F567\u002Frevisions\u002F673",[2160,2161],{"embeddable":120,"href":577},{"embeddable":120,"href":1368},[2163],{"href":2164},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fmedia?parent=567",[2166,2168],{"taxonomy":143,"embeddable":120,"href":2167},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fcategories?post=567",{"taxonomy":146,"embeddable":120,"href":2169},"https:\u002F\u002Fmarinemagnetics.com\u002Fcms\u002Fwp-json\u002Fwp\u002Fv2\u002Fapplication?post=567",[2171],{"name":150,"href":151,"templated":120},[2173,2176,2179],{"id":608,"name":2174,"slug":2175},"In-Action","in-action",{"id":32,"name":2177,"slug":2178},"News","news",{"id":330,"name":2180,"slug":2181},"Research","research",[2183,2186,2189,2192,2195,2198],{"id":610,"name":2184,"slug":2185},"Archeology","archeology",{"id":874,"name":2187,"slug":2188},"Cable + Pipeline","cable-pipeline",{"id":611,"name":2190,"slug":2191},"Environment Survey","environment-survey",{"id":713,"name":2193,"slug":2194},"Geophysical Exploration","geophysical-exploration",{"id":1571,"name":2196,"slug":2197},"Offshore Alt Energy","offshore-alt-energy",{"id":332,"name":2199,"slug":2200},"UXO","uxo"]