Reconstruction of electrical conductivity by EBA enhanced CSI method

We investigate the inverse problem of electromagnetic induction measurements by using the improved extended Born approximation (EBA) (see Habashy, T.M., J. Geoph. Res.-Solid Earth, vol.98, p.1759-75, 1993) and the contrast source inversion (CSI) method (see van den Berg, P.M. and Kleinman, R.E., Inverse Problems, vol.13, p.1607-20, 1997). For many problems, the two-step inversion method suffices. In very high contrast cases, where further improvement is needed, we apply the CSI method. However, rather than using back-propagation as the initial solution, we use the EBA inversion results as an initial profile to the nonlinear CSI method. The CSI method also uses the efficient conjugate gradient procedure and the FFT algorithm. In our implementation, this inverse method can solve typical electromagnetic induction problems with a contrast as high as 100:1.