THEMIS Flux Gate Magnetometer (FGM) measures the background magnetic field and any low frequency (to 64 Hz) fluctuations superimposed upon it. The FGM can detect variations in the magnetic field within the accuracy of 0.01 nT. The THEMIS FGM uses an updated technology developed in Germany that digitizes the sensor signals directly and replaces the analog hardware by software. Using the digital fluxgate technology results in lower mass of the instruments and improved robustness.

Development Institution: Technical University of Braunschweig, (TU-BS), Germany
FGM Lead: K. H. Glassmeier (TUBS)

The data are transimitted as several different types that vary in time resolution and availability. The fluxgate magnetometer engineering (FGE) quantity is available only during enginneering triggers(typically during perigee). FGE is provided at 1/8 second resolution, but is generally not processed to scientific quality standards. The fluxgate magnetometer low resolution data (FGL) is available during THEMIS fast survey mode. FGL is provided at 1/4 second time resolution. The FGL data is spin-phase corrected and calibrated on the ground for use in scientific data analysis. The fluxgate magnetometer high resolution data is available during THEMIS particle burst mode. It is provided at 1/128 second resolution. The FGH data is spin-phase corrected and calibrated on the ground for use in scientific data analysis. The fluxgate magnetometer spin fit data (FGS) is available at all times. It is provided at 3 second resolution; the nominal period of one THEMIS spacecraft resolution. FGS data is spin-phase corrected on-board. The equatorial correction is done using an A+Bsin(theta)+Ccos(theta) correction. Theta is the spinphase and a 0 spinphase is defined to be at the sunpulse. The Coefficients A,B, & C that were used in spin-phase correction can be found in the THEMIS level 1 FIT data CDF. The axial component of the FGS data is generated by taking the average of the z measurements over each spin. Additional calibrations and cleanup of FGS data may also be performed on the ground. All data types are provided in Despun Spacecraft L-Vector Corrected (DSL), Geocentric Solar Eclipitic(GSE), and Geocentric Solar Magnetospheric(GSM) coordinates. Information about the requested spacecraft mode can be found associated with the THEMIS housekeeping data CDF. The housekeeping cdf stores engineering quantities.