Quantitative multi-layer conductivity inversion of multi-configuration electromagnetic induction measurements

Electromagnetic induction (EMI) measurements return an apparent electrical conductivity (ECa) that represents a weighted average of the electrical conductivity distribution over a certain depth range [1]. Different sensing depths are obtained for different orientations, different coil offsets, and different frequencies, which can in principle be used for a multi-layer inversion. However, instrumental shifts, which often occur in EMI data, prevent the use of quantitative multi-layer inversion. Here, we apply a new calibration method that uses electrical resistivity tomography (ERT) inversion results and returns quantitative ECa values [2]. These calibrated multi-configuration EMI data can be fitted with a Maxwell-based electromagnetic horizontally layered forward model to obtain a layered subsurface [3]. Recently, a novel quasi three-dimensional imaging algorithm was implemented that uses quantitative multi-configuration EMI data to reconstruct lateral and vertical electrical conductivity patterns that can be used for large-scale high resolution catchment characterization. At each inversion location a three-layer electrical conductivity model is obtained that are stitched together to form a quasi-3D subsurface [4]. The layer-wise electrical conductivities are related to changes in soil water content, soil-texture and salinity.

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[4] C. von Hebel, S. Rudolph, A. Mester, J. A. Huisman, P. Kumbhar, H. Vereecken, J. van der Kruk, 2014, Three-dimensional imaging of subsurface structural patterns using quantitative large-scale multi-configuration electromagnetic induction data, Water Resources Research, 50, 2732-2748, doi:10.1002/2013WR014864

[3] A. Mester, J. van der Kruk, E. Zimmermann, H. Vereecken, 2011, Quantitative two-layer conductivity inversion of multi-configuration electromagnetic induction measurements, Vadose Zone Journal, 10, 1319 1330, doi:10.2136/vzj2011.0035

[2] F. Lavoue, J. van der Kruk, J. Rings, F. Andre, D. Moghadas, J. A. Huisman, S. Lambot, L. Weihermuller, J. vanderBorght, H. Vereecken, 2010, Electromagnetic Induction Calibration using Apparent Conductivity Modeling Based on Electrical Resistivity Tomography, Near Surface Geophysics, Vol. 8, pp. 553-561, doi: 10.3997/1873-0604.2010037

[1] J. van der Kruk, J.A.C. Meekes, P.M. van den Berg and J.T. Fokkema, 2000, An apparent resistivity concept for low frequency electromagnetic sounding techniques, Geophysical Prospecting, Vol. 48, pp. 1033-1052, doi: 10.1046/j.1365-2478.2000.00229.x.