A Swarm lithospheric magnetic field model to SH degree 80

Erwan Thébault,Gauthier Hulot,Benoit Langlais,Pierre Vigneron

doi:10.1186/s40623-016-0510-5

Abstract

The Swarm constellation of satellites was launched in November 2013 and since then has delivered high-quality scalar and vector magnetic field measurements. A consortium of several research institutions was selected by the European Space Agency to provide a number of scientific products to be made available to the scientific community on a regular basis. In this study, we present the dedicated lithospheric field inversion model. It uses carefully selected magnetic field scalar and vector measurements from the three Swarm satellites between March 2014 and December 2015 and directly benefits from the explicit expression of the magnetic field gradients by the lower pair of Swarm satellites. The modeling scheme is a two-step one and relies first on a regional modeling approach that is very sensitive to small spatial scales and weak signals which we seek to describe. The final model is built from adjacent regional solutions and consists in a global spherical harmonics model expressed between degrees 16 and 80. The quality of the derived model is assessed through a comparison with independent models based on Swarm and the CHAMP satellites. This comparison emphasizes the high level of accuracy of the current model after only 2 years of measurements but also highlights the possible improvements which will be possible once the lowest two satellites reach lower altitudes.

Highlights

The magnetic field of the Earth’s crust has spatial scales ranging from meters to 1000s of kilometers [e.g., Thébault et al (2010b) for a review]
Since the core and external fields mask the contributions of the lithosphere, current practice is to map the lithospheric field in spherical harmonics (SH) either by a joint inversion with other source magnetic fields or only after the measurements are corrected for the core and external fields
Differences are strongest in the northern and southern polar regions where rapid and significant non-lithospheric contributions in the measurements lead to arbitrary offsets between adjacent tracks that persist despite dedicated corrections and filtering

Summary

Introduction

The magnetic field of the Earth’s crust has spatial scales ranging from meters to 1000s of kilometers [e.g., Thébault et al (2010b) for a review]. To minimize its adverse effect, we first subtract the lithospheric field contribution from SH degrees 16–45 of the model derived in process 2 from the scalar and vector measurements before estimating the alongtrack correction.

Results

Conclusion