Magnetic-field estimation using measurements from a floating buoy

Magnetic-field fluctuations caused by solar storms can overload and destroy transformers, power grids and sensitive instrumentation on satellites, planes, and ships. To monitor these magnetic-field fluctuations, it is proposed to install magnetometers on floating buoys in the oceans. To obtain meaningful measurements from these magnetometers, it is important to know the orientation of the axes of the magnetometers with respect to the Earth. In this paper, we estimate the orientation of a floating buoy with respect to Earth using gyro measurements of angular velocity of the buoy. Since the angular position states are unobservable from the angular velocity measurements, we construct an additional fictitious measurement based on physical insights. In addition, to accommodate the additional fictitious measurement, we use an alternative nonlinear model for the buoy dynamics and use nonlinear filtering techniques to estimate the orientation of the buoy.