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

Abstract. The space-borne fluxgate magnetometer (FGM) needs regular in-flight calibration to obtain its zero offset. Recently, a new method based on the properties of Alfvén waves for the zero offset calibration was developed by Wang and Pan (2021). They found that there exists an optimal offset line (OOL) in the offset cube for a pure Alfvén wave, and the zero offset can be determined by the intersection of at least two non-parallel OOLs. Since no pure Alfvén waves exist in the interplanetary magnetic field, the calculation of the zero offset relies on the selection of the highly Alfvénic fluctuation event. 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) selection of highly Alfvénic fluctuation events, (2) evaluation of the OOL of the selected fluctuation events, and (3) determination of the zero offset. We test our automatic procedure by applying it to the magnetic field data measured by the FGM onboard Venus Express. The tests reveal that our automatic procedure is able to achieve as good results as the Davis-Smith method. One advantage of our procedure is that the selection criteria and process for the highly Alfvénic fluctuation event are simpler. Our automatic procedure might also be applied to find fluctuation events for the Davis-Smith method after proper modification.