A New Method to Calculate the Fluxgate Magnetometer Offset in the Interplanetary Magnetic Field: 1. Using Alfven Waves

Magnetic field measurements are essential to explore space. However, the measurement of the fluxgate magnetometer (FGM) is not zero in the null magnetic field. Three methods have been provided to calculate the zero offset of the FGM on-board spacecraft in the solar wind based on the assumption that the fluctuations are Alfven waves. Here, we develop a new method to calculate the zero offset O based on the characteristic of Alfven waves. We first build an offset cube based on the possible range of O since the strength of the interplanetary magnetic field is limited. The variance of the modified B-T (marked as delta) at a point in the offset cube can be obtained. We find that the point with the minimum delta in each plane along a certain axis forms a straight line, which is referred to as the optimal offset line. Interestingly, this line crosses the point with a value equal to O, and its direction is associated with the ambient magnetic field of Alfven waves. We also find that different optimal offset lines have an intersection with a value of O, suggesting that these characteristics of the optimal offset line can be used to determine the zero offset of the FGM. The test results show that our method can get a zero offset with a high accuracy. We suggest that the new method is a useful technique to find the zero offset of the magnetometer for solar wind monitors.