Survey of the magnetic signature of a moving surface vessel by multiple AUVs

A formation of autonomous underwater vehicles (AUVs) equipped with magnetometers has been used to perform a magnetic field survey of a moving surface vessel. The vessel had a nonmagnetic fiberglass hull. A permanent magnet with a known dipole moment was placed at the bow and a small intrinsic field was measured near the stern of the surface vessel. Measurements were taken at various surface vessel orientations, AUV orientations, and AUV depths. The measured field survey was compared to the fields predicted by a dipole model of the permanent magnet with an RMS error between measured and predicted fields of 3.04 nT in the vicinity of the surface vessel. The measured fields were also used to reconstruct a two-dipole model for the surface vessel accounting for the permanent magnet and the intrinsic field with an RMS error between the measured field and the model field of 2.13 nT in the vicinity of the surface vessel. The two-dipole reconstruction solution contained a dipole at a position very close to the permanent magnet on the surface vessel bow and an additional dipole at a position reasonably close to the stern of the boat.