Articles | Volume 35, issue 1
Ann. Geophys., 35, 117–121, 2017
Ann. Geophys., 35, 117–121, 2017

ANGEO Communicates 19 Jan 2017

ANGEO Communicates | 19 Jan 2017

Spin axis offset calibration on THEMIS using mirror modes

Dennis Frühauff1, Ferdinand Plaschke2, and Karl-Heinz Glassmeier1 Dennis Frühauff et al.
  • 1Institut für Geophysik und extraterrestrische Physik, Braunschweig, Germany
  • 2Space Research Institute, Austrian Academy of Sciences, Graz, Austria

Abstract. A newly developed method for determining spin axis offsets of magnetic field instruments on spacecraft is applied to THEMIS. The formerly used determination method, relying on solar wind Alfvénic fluctuations, was rarely applicable due to the orbital restrictions of the mission. With the new procedure, based on magnetic field observation of mirror modes in the magnetosheath, updated spin axis offsets can be estimated approximately once per year. Retrospective calibration of all THEMIS magnetic field measurements is thereby made possible. Since, up to this point, spin axis offsets could hardly ever be calculated due to the mission's orbits, this update represents a substantial improvement to the data. The approximate offset stability is estimated to be < 0.75 nT year−1 for the complete course of the mission.

Short summary
Vector magnetic field instruments mounted on spacecraft require precise in-flight calibration of the offsets of all three axes, i.e., the output in vanishing ambient field. While calibration of the spin plane offsets is trivial, we apply a new technique for determining the spin axis offset, not relying on solar wind data but on magnetosheath encounters. This technique is successfully applied to the satellites of the THEMIS mission to update the calibration parameters of the complete mission.