Calibration and localization of AUV-acquired magnetic survey data

A system is being developed to enable the measurement of the magnetic signature of a surface vessel at forward locations. The system consists of a fleet of AUVs (Autonomous Underwater Vehicles) each equipped with a magnetometer. A magnetic signature measurement would be performed in a coordinated relative movement between the fleet and the surface vessel. The precision of the magnetometer system and the precision of each position associated with magnetic measurements in a survey are crucial to the value of this measurement. Results of experiments on these two issues are reported. Calibrations of the AUV/magnetometer systems are performed in-situ and on land and are characterized by a noise floor of less than 10 nT. In experiments performed at a deepwater facility free from extraneous ambient magnetic sources, an AUV passed near a known magnetic source at a fixed location and orientation. Measurements of magnetic field and position estimates based upon navigation data acquired by the AUV were associated. An independent, high-accuracy acoustic tracking system was used during the experiments to determine a ground truth position for the AUV. The predicted magnetic field at the AUV estimated position was compared to the magnetic field acquired by the AUV near the source and found to have an error of 15 nT.