Magnetic Survey Techniques

🚀Magnetometer Madness: From Standalone Sensors to the SCM Revolution Offshore UXO and geohazard surveys demand precision, and the choice of magnetometer can make all the difference. Over time, surveyors have moved from standalone magnetometers to twin-vectored gradiometers (TVGs), advanced Scanfishes, and now Self-Compensating Magnetometers (SCMs)—a game-changer in the field. Standalone magnetometers 🎯 have been the go-to for years. Simple, reliable, and cost-effective, they detect ferrous objects beneath the seabed. However, they struggle with noise, heading errors, and coverage gaps, making QA/QC a challenge. They work best for small-scale operations where absolute precision isn’t critical. TVGs ⚡ improved on this by using two sensors at a fixed distance to measure magnetic gradients. By canceling out background noise, they enhance target resolution and depth discrimination. Though better than a single sensor, they still require careful calibration and remain sensitive to vessel-induced interference. For larger-scale operations, Scanfishes 🦑 changed the game. These hydrodynamically stable towfish-mounted arrays cover vast areas efficiently, mapping UXO and geohazards with greater accuracy. However, they come with operational complexity, requiring skilled handling and sophisticated post-processing. Strong currents and drag effects also add to the challenge. Now, SCMs 🚀 are rewriting the rulebook. Unlike traditional systems, they self-correct in real-time, eliminating heading errors and reducing false positives. Their high sensitivity allows for the detection of smaller and deeper objects with unprecedented accuracy. They integrate seamlessly with AUVs, USVs, and towed platforms like EIVA's ROTV to constitute a Hypermag (image below), making them the gold standard for offshore site characterization. Faster, more precise, and less reliant on post-processing, SCMs are revolutionizing UXO detection and geohazard mapping. The days of relying on single-sensor setups are fading. TVGs and Scanfishes still serve a purpose for the time being, but in my opinion, SCMs set a new benchmark for offshore geophysical surveys. As technology evolves, those who will embrace self-compensating magnetometers on towed vehicles or autonomous solutions will lead the way in precision, efficiency, and survey success. 🚢🔍 Image Credit Goes to: EIVA a/s, Geometrics Inc. Ocean Floor Geophysics #Oceanmapping #UXO #Survey #Hydrospatial #Hypermag #Geophysical #ALARP

❓ Did you know…   That drone magnetometry can be used not only for UXO or utilities but also for archaeology?   Drone-based magnetometry, as Ludwig-Maximilians-Universität München demonstrated at the Roman fortress of Theilenhofen, opens up new possibilities for noninvasive surveys of historical sites. The University had used ground-based magnetometers before, but they decided to use drones this time. Drone magnetometry helped cover large, difficult-to-access areas and identify major archaeological features (ditches, fireplaces, etc). This guided detailed ground-based surveys, significantly saving archaeologists' time.   The toolset included DJI M300 RTK drone, SPH Engineering Skyhub onboard computer, SENSYS - Magnetometers & Survey Solutions MagDrone R4 magnetometer, and MagDrone DataTool for data processing. 

Coastal #magnetometer surveys using traditional towed and airborne magnetometers. My article in EAGE (European Association of Geoscientists and Engineers) First Break journal - https://lnkd.in/dPCjZr4i Sean Zandbergen from Shore Monitoring & Research shared with me details of the project with aim to detect cables and pipelines before construction of new wind farm export cable. They used Geometrics Inc. G-882 towed marine magnetometer in deep part of survey area and airborne system with SPH Engineering #MagNIMBUS magnetometer to collect the data in shallow part.

🔵 𝗚𝗘𝗢𝗣𝗛𝗬𝗦𝗜𝗖𝗔𝗟 𝗠𝗘𝗧𝗛𝗢𝗗𝗦 𝗘𝗫𝗣𝗟𝗔𝗡𝗔𝗧𝗜𝗢𝗡: 𝗙𝗿𝗼𝗺 𝗙𝘂𝗻𝗱𝗮𝗺𝗲𝗻𝘁𝗮𝗹𝘀 𝘁𝗼 𝗘𝘅𝗽𝗹𝗼𝗿𝗮𝘁𝗶𝗼𝗻 𝗜𝗺𝗽𝗮𝗰𝘁🛢️ Here’s your ultimate guide to four core geophysical methods—each packed with their scientific principle, survey method, operative physical property and key applications in the oil & gas industry (and beyond). ━━━━━━━━━━━━━━━━━━━━━━ ➤ MAGNETIC METHOD ━━━━━━━━━━━━━━━━━━━━━━ 🔹 Principle: Detects variations in Earth's magnetic field caused by contrasts in magnetic susceptibility. 🔹 Survey Tool: Ground, airborne or marine magnetometers. 🔹 Physical Property: Magnetic susceptibility 🔸 Oil & Gas Applications: → Mapping basement structures and fault zones → Detecting igneous intrusions (potential traps) 🔸 Other Uses: → Mineral exploration (e.g. magnetite, Cu-Au) → Buried object detection in archaeological and environmental studies ━━━━━━━━━━━━━━━━━━━━━━ ➤ GRAVITY METHOD ━━━━━━━━━━━━━━━━━━━━━━ 🔹 Principle: Measures slight changes in gravitational acceleration caused by underground density contrasts. 🔹 Survey Tool: Ground or airborne gravimeters. 🔹 Physical Property: Rock density 🔸 Oil & Gas Applications: → Mapping salt domes and reservoir structures → Structural basin modeling for prospect delineation 🔸 Other Uses: → Locating dense mineral bodies (e.g. iron, base metals) → Geotechnical void mapping and archaeological detection ━━━━━━━━━━━━━━━━━━━━━━ ➤ ELECTROMAGNETIC METHOD (EM) ━━━━━━━━━━━━━━━━━━━━━━ 🔹 Principle: Applies time-varying EM fields to induce currents and measure resulting conductivity or resistivity. 🔹 Survey Tools: TEM, FDEM, marine CSEM, airborne EM and MT for deep targets. 🔹 Physical Property: Electrical conductivity / resistivity 🔸 Oil & Gas Applications: → Marine CSEM to map resistive hydrocarbon layers → Magnetotellurics (MT) for geothermal and deep basin analysis 🔸 Other Uses: → Mapping groundwater and contamination plumes → Detecting buried infrastructure in urban areas ━━━━━━━━━━━━━━━━━━━━━━ ➤ SEISMIC METHOD ━━━━━━━━━━━━━━━━━━━━━━ 🔹 Principle: Sends seismic waves (P, S) into the Earth to analyze reflections and refractions caused by changes in elastic properties. 🔹 Survey Tools: Controlled sources (vibrators, explosives, air guns) + receivers (geophones/hydrophones). 🔹 Physical Property: Acoustic velocity, density, impedance 🔸 Oil & Gas Applications: → 2D/3D reservoir imaging and structural delineation → Velocity models for safe and accurate drilling 🔸 Other Uses: → Earthquake studies and tectonic analysis → Fluid detection via emerging seismoelectric techniques ━━━━━━━━━━━━━━━━━━━━━━ Final Thought: Geophysical tools don’t just “see” underground—they interpret Earth’s hidden stories using physics, precision and data. Mastering these methods opens doors across exploration, engineering and environmental impact. #Geophysics #OilAndGasExploration #MagneticSurvey #GravityMethod #EMSurvey #SeismicExploration #SubsurfaceImaging #CSEM #Geoscience