ELECTROMAGNETIC CONDUCTIVITY IMAGING WITH AN ITERATIVE BORN INVERSION

A technique is developed which uses low frequency electromagnetic (EM) fields to image the earth's conductivity structure between tow boreholes. The scheme employs the Born approximation to linearize the integral equation formulation, and a regularized least squares method to invert the data for an initial estimate of the conductivity. A second Born approximation is then applied in a iterative manner to achieve better estimates of the structure. Numerical experiments show that this iterative method improves resolution when compared to normal Born inversion due to the fact that coupling between scattering currents is accounted for. The image quality is shown to be dependent on the operating frequency with the optimal frequency corresponding to the peak of a sensitivity function we have termed the Born kernel which is the product of the primary electric field and the Green's function.