AUV Towed Integration

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Using an AUV-Borne Magnetometer

Source: Doug Hrvoic, Marine Magnetics

Magnetometers have always been a particular challenge to mount on AUV’s, because of their strong magnetic signatures, until now. To solve the problem an AUV was needed whose magnetism was mild at best, and a magnetometer was needed that was free from dead zones, was small, low powered and free from heading errors and orientation restrictions. Together the Iver2 AUV and Explorer AUV magnetometer create the perfect combination.

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Hrvoic 2014 Geophysical Survey using AUV with Magnetometer and Sidescan Sonar

Small, low cost Autonomous underwater vehicles (AUVs) provide ideal platforms for shallow water survey, as they are capable of unmanned navigation and can be programmed to acquire data at constant depth, or constant altitude above the seabed. AUVs can be deployed under most sea states and are unaffected by vessel motions that often degrade sonar and magnetometer data quality. The integration of sonar and magnetometer sensors on AUV’s is challenging, however, due to limited payload and strong magnetic fields produced by the vehicle motor. In this study, a Marine Magnetics Explorer Overhauser magnetometer was mated to a portable AUV (OceanServer Iver2) creating the first practical AUV-deployed magnetic survey system. To eliminate magnetic interference from the AUV, the magnetometer was tethered to the AUV with a 5 m tow cable, as determined by static and dynamic instrument testing. The results of the magnetic tests are presented, along with field data from a shallow water test area in Lake Ontario near Toronto, Canada. AUV-acquired magnetic survey data were compared directly with a conventional boat-towed magnetic survey of the same area. The AUV magnetic data were of superior quality despite being collected in rough weather conditions that would have made conventional survey impossible. The resulting high-resolution total magnetic intensity and analytic signal maps clearly identify several buried and surface ferrometallic targets that were verified in 500-kHz side-scan sonar imaging and visual inspection by divers.