Crustal magnetic field modelling to spherical harmonic degree 2000

Earth's crust provides a significant component of the geomagnetic field, which has large variation over short distances, but has negligible variation in time. Whether for precise direction seeking or geological surveying, this crustal field has a considerable human impact. The fine spatial scales involved mean that satellite data can only resolve longer-wavelength features, while the lack of time variation means that data accumulates over time. One of the key repositories of this collated data is the World Digital Magnetic Anomaly Map (WDMAM), produced by an international task force. In order to make use of this predominantly scalar data to obtain the full field at arbitrary locations, the British Geological Survey (BGS) produce a spherical harmonic model based on this data. Since 2019 this model has extended to spherical harmonic degree 1440, corresponding to a minimum wavelength of around 28 km. In 2023, an updated version of WDMAM was released, providing greater detail in many parts of the world. This coincides with an overhaul of the BGS crustal modelling code that has resulted in improved computational performance and the feasibility of computing very high resolution models. We thus evaluate the potential of a renewed crustal model up to degree 2000 (minimum wavelength around 20 km), and the inclusion of updated WDMAM data.