3-D electromagnetic induction studies using the Swarm constellation: Mapping conductivity anomalies in the Earth’s mantle

Abstract

Abstract An approach is presented to detect deep-seated regional conductivity anomalies by analysis of magnetic observations taken by low-Earth-orbiting satellites. The approach deals with recovery of C-responses on a regular grid and starts with a determination of time series of external and internal coefficients of the magnetic potential. From the coefficients, time series of the magnetic vertical component and of the horizontal divergence of the horizontal components are synthesized on the grid and the C-responses are determined by means of signal processing of the corresponding time series. For validation of the approach, 3 years of realistic synthetic data at simulated orbits of the forthcoming Swarm constellation of 3 satellites have been used. To obtain the synthetic data for a given 3-D conductivity Earth’s model a time-domain scheme has been applied which relies on a Fourier transformation of the inducing field, and on a frequency domain forward modelling. The conductivity model consists of a thin surface layer of realistic conductance and a 3-D mantle that incorporates a hypothetic deep regional anomaly beneath the Pacific Ocean plate. To establish the ability of the approach to capture the geometry of the mantle heterogeneities used in the forward approach, numerical experiments have been undertaken using various satellite combinations, sampling periods of the resulting time series, and numbers of internal coefficients. The possibility of the approach to map anomalies in the mantle using satellite data that contain contributions from the core and lithosphere, from the magnetosphere and ionosphere (and their Earth-induced counterparts), as well as payload noise has been investigated. The model studies have shown that C-responses obtained on a regular grid might be used to map regional deep-seated conductivity anomalies. Moreover, it has been demonstrated that these C-responses are successfully recovered from magnetic data collected by the proposed Swarm constellation of 3 satellites.