Abstract
Abstract. We compare the magnetic field data obtained from the flux-gate magnetometer (FGM) and the magnetic field data deduced from the gyration time of electrons measured by the electron drift instrument (EDI) onboard Cluster to determine the spin-axis offset of the FGM measurements. Data are used from orbits with their apogees in the magnetotail, when the magnetic field magnitude was between about 20 and 500 nT. Offset determination with the EDI–FGM comparison method is of particular interest for these orbits, because no data from solar wind are available in such orbits to apply the usual calibration methods using the Alfvén waves. In this paper, we examine the effects of the different measurement conditions, such as direction of the magnetic field relative to the spin plane and field magnitude in determining the FGM spin-axis offset, and also take into account the time-of-flight offset of the EDI measurements. It is shown that the method works best when the magnetic field magnitude is less than about 128 nT and when the magnetic field is aligned near the spin-axis direction. A remaining spin-axis offset of about 0.4 ∼ 0.6 nT was observed for Cluster 1 between July and October 2003. Using multipoint multi-instrument measurements by Cluster we further demonstrate the importance of the accurate determination of the spin-axis offset when estimating the magnetic field gradient.
Highlights
Methods and DataInterinstrument calibration using magnetic field data from the flux-gate magnetometer (FGM) and electron drift instrument (EDI)
Magnetic field and plasma environments of the Earth and other bodies in the solar system have been studied in situ since decades (Balogh, 2010)
Based on a simple comparison between the magnetic field of flux-gate magnetometer (FGM) and the magnetic field deduced from the time of flight of the electron drift instrument (EDI) measurements, we have shown that the remaining spin-axis offset of FGM data can be well determined from the calibrated data set by selecting the appropriate interval, by taking into account the measurement conditions such as the angle of the magnetic field relative to the spin-plane, magnetic field magnitude, and by considering the effect of the time-of-flight offset of the EDI measurement
Summary
Interinstrument calibration using magnetic field data from the flux-gate magnetometer (FGM) and electron drift instrument (EDI). Carr5 1Space Research Institute, Austrian Academy of Sciences, 8042 Graz, Austria 2Graz University of Technology, 8010 Graz, Austria 3University of New Hampshire, Durham, NH 03824, USA 4Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, 38106 Braunschweig, Germany 5Blackett Laboratory, Imperial College London, London, UK * at: Materials Center Leoben Forschung GmbH, Leoben, Austria. Received: 31 May 2013 – Published in Geosci. Discuss.: 30 July 2013 Revised: 13 December 2013 – Accepted: 15 January 2014 – Published: 22 January 2014. ∗∗ This paper is dedicated to the memory of Edita Georgescu
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