SOME METHODS FOR MAGNETOMETER ZERO-LEVEL DETERMINATION

Zero-level determination is an important aspect of the processing of m agnetometer 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 method s in addition to preflight calibration. Two different such techniques have been studied, taking advantage of observations made by instrument s other than the magnetometer. The first is based on measurements obta ined by electron drift instruments, originally designed to measure ele ctric fields. We shall discuss the applicability of such instruments t o determine magnetometer offsets. The second method is based on partic le pressure tensor measurements, where pressure anisotropy is used to determine the magnetic field direction.