Some methods for magnetometer zero-level determination

Zero-level determination is an important aspect of the processing of magnetometer observations made onboard spacecrafts. Due to the presence of instrument offset drift as well as magnetic fields produced by the spacecraft, such a zero-level determination requires in-flight methods in addition to preflight calibration. Two different such techniques have been studied, taking advantage of observations made by instruments other than the magnetometer. The first is based on measurements obtained by electron drift instruments, originally designed to measure electric fields. The authors discuss the applicability of such instruments to determine magnetometer offsets. The second method is based on particle pressure tensor measurements, where pressure anisotropy is used to determine the magnetic field direction.