Use of Swarm gradient field data to improve lithospheric field models

The Swarm mission, launched in November 2013, consists of three identical satellites designed to measure the magnetic field to the highest resolution ever. One of the Swarm mission's unique aspects is the ability to measure the magnetic field at approximately the same location using two satellites (Swarm A and Swarm C) which travel close to one another at the same altitude. Using measurements of the gradient of the field between the satellites (i.e. across-track) removes much of the external magnetic field's influence in the data, leaving the contribution from the steady internal field, each time the satellites pass over the same location [Ref. 1]. In combination with measurements of the satellites’ along-track differences this adds a new capability that can be exploited to produce models of the crustal magnetic field with higher accuracy than ever before. As the mission accumulates more data at lower altitudes, our understanding of the Earth’s magnetic field will continue to improve. We apply a Slepian decomposition technique to the new BGS lithospheric field model to analyse the relative contributions to the magnetic field from the ocean and continents, which may be useful for geological applications.