Abstract
Abstract. Accurate magnetic field measurements by fluxgate magnetometers onboard spacecraft require ground and regular in-flight calibration activities. Therewith, the parameters of a coupling matrix and an offset vector are adjusted; they are needed to transform raw magnetometer outputs into calibrated magnetic field measurements. The components of the offset vector are typically determined by analyzing Alfvénic fluctuations in the solar wind if solar wind measurements are available. These are characterized by changes in the field components, while the magnetic field modulus stays constant. In this paper, the following question is answered: how many solar wind data are sufficient for accurate fluxgate magnetometer offset determinations? It is found that approximately 40 h of solar wind data are sufficient to achieve offset accuracies of 0.2 nT, and about 20 h suffice for accuracies of 0.3 nT or better if the magnetometer offsets do not drift within these time intervals and if the spacecraft fields do not vary at the sensor position. Offset determinations with uncertainties lower than 0.1 nT, however, would require at least hundreds of hours of solar wind data.
Highlights
In situ investigations of the plasma environments of planets, moons, comets, or other solar system bodies require magnetic field measurements by spacecraft magnetometers
The required measurements can only be provided if those magnetometers are accurately calibrated. This means that a coupling matrix C and an offset vector O have to be accurately known in order to transform raw magnetometer outputs Braw into calibrated magnetic field measurements B
If the spacecraft is non-spinning, i.e., three-axis stabilized, the following methods can be used for offset determination: (1) Alfvénic fluctuations that are abundant in the solar wind are characterized by changes in the magnetic field components, while the field magnitude stays constant
Summary
In situ investigations of the plasma environments of planets, moons, comets, or other solar system bodies require magnetic field measurements by spacecraft magnetometers. If the spacecraft is non-spinning, i.e., three-axis stabilized, the following methods can be used for offset determination: (1) Alfvénic fluctuations that are abundant in the solar wind are characterized by changes in the magnetic field components, while the field magnitude stays constant. An analysis of such fluctuations allows for an adjustment of the offsets through minimization of the changes in the magnetic field magnitude (e.g., Belcher, 1973; Hedgecock, 1975; Leinweber et al, 2008). It shall address the following question: how many solar wind data are needed to obtain all three components of the offset vector with a certain accuracy? The latter assumption means that the spacecraft spin cannot be used to support the determination of the spin plane offset components
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