Automatic calculation of the magnetometer zero offset using the interplanetary magnetic field based on the Wang–Pan method

The space-borne fluxgate magnetometer (FGM) requires regular in-flight calibration to obtain its zero offset. Recently, Wang GQ and Pan ZH (2021a) developed a new method for the zero offset calibration based on the properties of Alfvén waves. They found that an optimal offset line (OOL) exists in the offset cube for a pure Alfvén wave and that the zero offset can be determined by the intersection of at least two nonparallel OOLs. Because no pure Alfvén waves exist in the interplanetary magnetic field, calculation of the zero offset relies on the selection of highly Alfvénic fluctuation events. Here, we propose an automatic procedure to find highly Alfvénic fluctuations in the solar wind and calculate the zero offset. This procedure includes three parts: (1) selecting potential Alfvénic fluctuation events, (2) obtaining the OOL, and (3) determining the zero offset. We tested our automatic procedure by applying it to the magnetic field data measured by the FGM onboard the Venus Express. The tests revealed that our automatic procedure was able to achieve results as good as those determined by the Davis–Smith method. One advantage of our procedure is that the selection criteria and the process for selecting the highly Alfvénic fluctuation events are simpler. Our automatic procedure could also be applied to find fluctuation events for the Davis–Smith method.