Numerical modeling for electromagnetic remote sensing of inhomogeneities in the ground

After a brief description of the mathematical formulation, we show some of the benefits that can be derived from numerical models. One of these benefits is to furnish an estimation of the suitability of electromagnetic prospecting methods with regard to specific sounding tasks. Using as an example the detection of a magma pocket with a line-source of current or an electric antenna as excitation, we also call attention to the limit of validity of two-dimensional models. Then, we consider the remote sensing, from the earth's surface, of cavities embedded at small depths. We point out the disturbing effect of a conducting overburden on the efficiency of electromagnetic methods. A three-loop system is proposed and the various prospecting parameters of this system are conveniently optimized with the help of the numerical model. This three-loop system is then shown to be far superior to the standard two-loop method.