Optimized Merging of Search-Coil and Fluxgate Data for the Magnetospheric Multiscale Mission

he main objective of the Magnetospheric Multiscale (MMS) mission is to characterize fine-scale structures in the Earth?s magnetotail and magnetopause. These dynamic structures traverse the MMS spacecraft formation at high speed and generate magnetic field signatures that cross the sensitive frequency bands of both search-coil and fluxgate magnetometers. An improved understanding of these events is only possible by combining data from both instrument types for magnetospheric event analysis. This combination is done using a model-based sensor fusion approach that merges data from both instrument types to a virtual instrument with flat gain curve, linear phase and known timing properties as well as the highest sensitivity and lowest noise floor. The generation of the underlying instrument models requires precise knowledge of the instrument frequency responses and timing. This knowledge was obtained in a dedicated end-to-end measurement campaign using a purpose-built magnetic field source tightly coupled to the MMS time standard. Sensor fusion is embedded in a carefully designed setup that minimizes processing artefacts and which is suitable for automated execution. This setup uses the instrument models for frequency response compensation and merges the data using complementary filters based on instrument sensitivity and noise floor. The precision of the resulting merged data set has been demonstrated by comparison of in-flight data. This comparison shows an unchanged DC and low frequency gain, an AC gain accuracy that is better than 1% for higher frequencies and a phase delay uncertainty below 100 ?s. The models, filters and data processing algorithms developed in this thesis are applied in the generation of the official fluxgate-search-coil merged data product, which is available for public use at the MMS science data center. With the work done in this thesis, MMS is the first space mission that is able to provide a high precision merged magnetic field data product. It is an excellent tool to answer questions that are on the borders of knowledge in current plasma science, e.g., the existence of reconnection in the turbulent magnetosheath or the properties of dipolarization fronts with associated whistler mode wave emissions.