3-D finite difference iterative migration of the electromagnetic field

In this paper we introduce a method for the iterative migration of the electromagnetic (EM) field. It is based on the regularized conjugate gradient (RCG) algorithm and finite difference (FD) modeling. In the framework of this approach, the FD forward operator is used twice per frequency in each iteration step. First, we apply the FD forward operator to compute the predicted field for a given conductivity distribution. The residual field is then computed by taking the difference between the observed and predicted data. Second, the FD forward operator is utilized to migrate the residual field in the lower half-space. Thus, the iterative migration method requires just two FD forward solutions per frequency, per iteration.