A high-resolution lithospheric magnetic field model over southern Africa based on a joint inversion of CHAMP, Swarm, WDMAM, and ground magnetic field data

Foteini Vervelidou,Erwan Thébault,Monika Korte

doi:10.5194/se-9-897-2018

Abstract

Abstract. We derive a lithospheric magnetic field model up to equivalent spherical harmonic degree 1000 over southern Africa. We rely on a joint inversion of satellite, near-surface, and ground magnetic field data. The input data set consists of magnetic field vector measurements from the CHAMP satellite, across-track magnetic field differences from the Swarm mission, the World Digital Magnetic Anomaly Map, and magnetic field measurements from repeat stations and three local INTERMAGNET observatories. For the inversion scheme, we use the revised spherical cap harmonic analysis (R-SCHA), a regional analysis technique able to deal with magnetic field measurements obtained at different altitudes. The model is carefully assessed and displayed at different altitudes and its spectral content is compared to high-resolution global lithospheric field models. By comparing the shape of its spectrum to a statistical power spectrum of Earth's lithospheric magnetic field, we infer the mean magnetic thickness and the mean magnetization over southern Africa.

Highlights

The increasing availability of magnetic field measurements, both at satellite altitude and near or at the Earth’s surface, makes it possible to improve models of the lithospheric magnetic field periodically, both in terms of accuracy and spatial resolution
We focus on the southern part of Africa, which is well covered by near-surface measurements, and we opt for the revised spherical cap harmonic analysis (RSCHA, Thébault et al, 2006) for modeling the lithospheric magnetic field
In this study we jointly modeled satellite, aeromagnetic, marine, and ground magnetic field measurements and derived a lithospheric magnetic field model over southern Africa

Summary

Introduction

The increasing availability of magnetic field measurements, both at satellite altitude and near or at the Earth’s surface, makes it possible to improve models of the lithospheric magnetic field periodically, both in terms of accuracy and spatial resolution. Low Earth orbiting magnetic satellite missions, such as CHAMP (Reigber et al, 2002) and the ongoing multi-satellite mission Swarm (Friis-Christensen et al, 2006; Olsen et al, 2013), complement near-surface measurements by offering a consistent global view of the large-scale features of the lithospheric magnetic field. Based on a different way of processing and merging the marine and aeromagnetic measurements, Maus et al (2009) derived another anomaly grid, the EMAG2, which was converted by Maus (2010) to an SH model up to degree 720

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Conclusion