Real-Time Reconstruction of the Eddy-Current Magnetic Field in a Local Region of a Maneuvering UUV Platform

When an unmanned underwater vehicle (UUV) with an aluminum-alloy hull maneuvers, its motion through the geomagnetic field generates an eddy-current magnetic field that interferes with the onboard magnetometer. We propose a method that extracts a low-dimensional spatial basis offline and reconstructs the eddy-current field within a local region online with two magnetometers. Offline, transient finite element method (FEM) simulations with unit excitations along the three body axes provide a quasi-static mode and a relaxation mode per excitation channel together with their step responses. Online, the time derivative of the primary magnetometer output drives a feed-forward reconstruction through the step responses, and the differential measurement of a single auxiliary magnetometer gives one amplitude factor, estimated sample by sample, that corrects the amplitude deviation of the offline model. The method requires neither angular-rate measurements nor calibration maneuvers. Six spatial modes represent the field of yaw, pitch, and roll maneuvers over the entire sensor candidate region with an error below 0.8%, and that of a combined reversing maneuver exciting all three channels with an error of 1.2%. With five classes of magnetometer error and two classes of model error injected, the region reconstruction error is 2.7–3.2% under a favorable installation and 6.1–7.3% under a typical installation. The residual at the primary magnetometer, the eddy-current interference remaining after vector compensation, is 8–9 nT and 14–15 nT. Open-loop feed-forward reconstruction yields 9.7–10.9%, and the complete Tolles–Lawson model calibrated on six other maneuvers yields 9–10 nT and 13–14 nT. In a further test, an independent FEM model with a 10% lower conductivity, an added conductor, and a new mesh generates the data, while the method keeps the original offline model. The amplitude factor converges to 0.90, the true ratio between the fields of the two models, and the residual stays within 4–10 nT. After the primary magnetometer is relocated, the residual without recalibration is 10 nT for the proposed method and 25–40 nT for the Tolles–Lawson model calibrated at the original position.