The THEMIS Flux Gate Magnetometer (FGM) measures the background magnetic field and its low frequency fluctuations (up to 64 Hz) in the near-Earth space. FGM is specifically designed to study abrupt reconfigurations of the Earth's magnetosphere during the substorm onset phase. This requires an exceptional offset stability of 0.2 nT/hour. Due to its high sensitivity the FGM is capable to detect variations of the magnetic field with amplitudes of 0.01 nT. For attitude determination purposes the FGM must also operate close to the Earth at field levels of about 25000 nT. Thus the FGM needs to measure fields in a range extending over six orders of magnitude.
FGM was developed at the Institute for Geophysics and Extraterrestrial Physics of TU Braunschweig. The calibration of the magnetometers was carried out in close cooperation with IWF.