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

The forward problem of calculating the electromagnetic (EM) fleld of a circular current loop in presence of a layered earth structure, given the geometrical and EM parameters of the layers, is solved fast. E-cient computation is obtained through a quasi- analytical procedure that allows to transform the fleld integrals into expressions involving only a known Sommerfeld Integral. The flnal explicit forms of the flelds are in terms of modifled Bessel functions. To validate the method, the magnitudes of the EM fleld 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 fllter algorithms. The computational time taken by the application of this technique is shown to be much less than that required by both digital fllters and other recently developed integration techniques for similar problems. This paper is an extension of an earlier conference paper.