A New Method of Fluxgate Magnetometer Offset Vector Determination in the Solar Wind Using Any Magnetic Field Variations

Abstract

In-depth study of dynamic processes in the astrophysical plasma environment relies on high-precision measurement of the magnetic field. Fluxgate magnetometers (FGMs) are commonly used on spacecraft to measure the magnetic field. However, their zero offsets vary slowly with time, and therefore need regularly in-flight calibration. Traditional methods of calculating the zero offset are based on properties of Alfvén waves, mirror mode structures, or current sheets. Here, we develop a new method of calculating the zero offset using any interplanetary magnetic field (IMF) variations. We create an offset cube according to the possible range of the IMF strength. The average values of B L for the IMF variation events approximately obey the normal distribution if there are enough events, where B L is the magnetic field in the maximum variance direction. Any constant vector added to the natural magnetic field data of the events will make the standard deviation of the normal distribution larger. Thereby, the point is determined to be the zero offset so that the corresponding standard deviation at this point is the minimum in the offset cube. Our test results show that this method has a 95.5% probability of obtaining the zero offset with an error of less than 0.3 nT when 10–21 hr of data are used. Our method provides an option for the in-flight calibration of the spaceborne FGM in the solar wind when there are not enough Alfvén waves, mirror modes, or current sheets.

Calibration of the Zero Offset of the Fluxgate Magnetometer on Board the Tianwen‐1 Orbiter in the Martian Magnetosheath

“…Using the data of B plus a constant vector in the spacecraft coordinate system, the distribution of 〈 B L 〉 also approximately obeys a normal distribution, but its standard deviation δ would change. Interestingly, δ has a minimum value when the constant vector is ≈ 0, which might be supported by the fact that the median is ∼0 for each component of the IMF over a long enough period (Wang, 2022b). Such a property can be used as an indicator to find out the zero offset of the spaceborne FGM (Wang, 2022b).…”

“…Interestingly, δ has a minimum value when the constant vector is ≈ 0, which might be supported by the fact that the median is ∼0 for each component of the IMF over a long enough period (Wang, 2022b). Such a property can be used as an indicator to find out the zero offset of the spaceborne FGM (Wang, 2022b).…”

“…For a certain subinterval, the average of the L component of the magnetic field 〈 B L 〉 can be calculated by MVA using the data during this whole subinterval. Wang (2022b) found that the distribution of 〈 B L 〉 approximately obeys a normal distribution if the number of the used subintervals is large enough. Using the data of B plus a constant vector in the spacecraft coordinate system, the distribution of 〈 B L 〉 also approximately obeys a normal distribution, but its standard deviation δ would change.…”

“…Figure 1 shows the diagram of the zero offset calculation of the Wang method II, which has three steps as follows (see Wang, 2022b). …”

“…Alfvén waves (Cheng et al., 2022; Davis & Smith, 1968; Meng et al., 2018; Pan et al., 2019; Wang & Pan, 2021a), mirror mode structures (Hu, Wang, Pan, & Zhang, 2022; Plaschke et al., 2017; Plaschke & Narita, 2016; Wang & Pan, 2021b), and current sheets (Wang & Pan, 2022) can be used to determine the zero offset of the spaceborne FGM. Table 1 lists the papers on the in‐flight calibration methods of FGMs, which can be divided into two groups: zero offsets determined by equations (Belcher, 1973; Davis & Smith, 1968; Hedgecock, 1975; Plaschke et al., 2017; Plaschke & Narita, 2016) and probabilities (Meng & Wang, 2023; Wang, 2022a, 2022b; Wang & Pan, 2021a, 2021b, 2022). Since the interplanetary magnetic field (IMF) is highly Alfvénic (see Leinweber et al., 2008), the methods based on Alfvén waves are suitable for the spacecraft in the solar wind.…”