A Parameterized Geometric Magnetic Field Calibration Method for Vehicles with Moving Masses with Applications to Underwater Gliders

The accuracy of magnetic measurements performed by autonomous vehicles is often limited by the presence of moving ferrous masses. This work proposes a third order parameterized ellipsoid calibration method for magnetic measurements in the sensor frame. In this manner the ellipsoidal calibration coefficients are dependent on the locations of the moving masses. The parameterized calibration method is evaluated through field trials with an autonomous underwater glider equipped with a low power precision fluxgate sensor. These field trials were performed in the East Arm of Bonne Bay, Newfoundland in December of 2013. During these trials a series of calibration profiles with the mass shifting and ballast mechanisms at different locations were performed before and after the survey portion of the trials. The nominal ellipsoidal coefficients were extracted using the full set of measurements from a set of calibration profiles and used as the initial conditions for the third order polynomials. These polynomials were then optimized using a gradient descent solver resulting in a RMS error between the calibration measurements and the local total field of 28 and 17 nT for the first and second set of calibration runs. When the parameterized coefficients are used to correct the magnetic measurements from the survey portion of the field trials the RMS error between the survey measurements and the local total field was 124 and 69 nT when using the first and second set of coefficients.