TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 65 (No. 11), pp. 1247-1256, 2013

Determination of the 3-D distribution of electrical conductivity in Earth's mantle from Swarm satellite data: Frequency domain approach based on inversion of induced coefficients

Christoph Püthe and Alexey Kuvshinov

ETH Zürich, Institute of Geophysics, Sonneggstrasse 5, 8092 Zürich, Switzerland

(Received December 17, 2012; Revised August 21, 2013; Accepted September 5, 2013; Online published November 22, 2013)

Abstract: Mapping the three-dimensional (3-D) electrical conductivity of Earth's mantle has been identified as one of the primary scientific objectives for the Swarm satellite mission. We present a 3-D frequency domain inversion scheme to recover mantle conductivity from satellite magnetic data. The scheme is based on an inversion of time spectra of internal (induced) spherical harmonic coefficients of the magnetic potential due to magnetospheric sources. Time series of internal and external (inducing) coefficients, whose determination is a prerequisite for this formulation, will be available as a Swarm Level-2 data product. An iterative gradient-type (quasi-Newton) optimization method is chosen to solve our 3-D non-linear inverse problem. In order to make the inversion tractable, we elaborate an adjoint approach for a fast and robust calculation of the data misfit gradient. We verify our approach with synthetic, but realistic time spectra of internal coefficients, obtained by simulating induction due to a realistic magnetospheric source in a 3-D conductivity model of the Earth. In these model studies, both shape and conductivity of a large-scale conductivity anomaly in the mid-mantle are recovered very well. The inversion scheme also shows to be robust with respect to noise and is therefore ready to process Swarm data.
Key words: 3-D electromagnetic induction, 3-D inversion, mantle conductivity anomalies, frequency domain.

Corresponding author E-mail: christoph.puethe@erdw.ethz.ch

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