Magnetic field surveys of coastal waters using an AUV-towed magnetometer

AUV-based measurement of the magnetic field offshore of South Florida is described. The effort is part of a measurement program involving observations from fixed and mobile sensor systems in the region in support of characterizing the local background magnetic field in coastal waters. A SeaSpy magnetometer is towed at some distance from a Bluefin 21 AUV in order that the measurements of the magnetic field are not corrupted by the magnetic noise onboard the AUV. The SeaSpy magnetometer has a sensitivity of 0.01nT and resolution of 0.001nT so that it can facilitate observations in the expected measurement range of interest, 0.01 - 1 nT. The AUV is equipped with onboard upward (600kHz) and downward (300kHz) looking ADCPs, and a CTD package which simultaneously provide the contextual in-situ oceanographic information, including temperature, salinity, and current velocity in the water column. Implementation of the towing system and the considerations given in making the implementation are described. Results from preliminary missions involving towing of the magnetometer in coastal waters are described.