Automatic parameterization for magnetometer zero offset determination

In-situ magnetic field measurements are of critical importance in understanding how the Sun creates and controls the inner heliosphere. In-flight it is necessary to track the combined slowly-varying spacecraft and magnetometer zero offset - the systematic error in the sensor measurements. For a 3-axis stabilised spacecraft, correction of zero offsets principally relies on the solar wind variance method, a technique that uses Alfvénic rotations in the magnetic field. We present a method to determine a key parameter related to the ambient compressional variance of the signal, which determines the selection criteria for identifying clear Alfvénic rotations. Due to the strong dependence on Alfvénicity, we show how frequently offsets can be calculated using our method at different heliocentric distances, using data from Helios. We compare our method with the previous fixed parameter approach and demonstrate an improvement in the probability of calculating an offset of up to 10%.