FAST COMPUTATION OF THE FORWARD SOLUTION IN CONTROLLED-SOURCE ELECTROMAGNETIC SOUNDING PROBLEMS

The forward problem of calculating the electromagnetic (EM) field of a circular current loop in presence of a layered earth structure, given the geometrical and EM parameters of the layers, is solved fast. Efficient computation is obtained through a quasi-analytical procedure that allows to transform the field integrals into expressions involving only a known Sommerfeld Integral. The final explicit forms of the fields are in terms of modified Bessel functions. To validate the method, the magnitudes of the EM field components versus induction number and versus frequency are calculated assuming two- and three-layer earth models. The achieved results are in good agreement with the ones provided by the commonly used digital filter algorithms. The computational time taken by the application of this technique is shown to be much less than that required by both digital filters and other recently developed integration techniques for similar problems. This paper is an extension of an earlier conference paper.