EMLCLLER—a program for computing the EM response of a large loop source over a layered earth model

Abstract

A simple program EMLCLLER coded in FORTRAN 77 is presented in this paper for modeling the electromagnetic (EM) response of a large circular loop source over a layered earth model in quasi-static as well as non-quasi-static (general frequency) regions. The program is based on a semi-analytical numerical approach for evaluating the improper integrals occurring in the expressions of EM field components. It takes into account both conduction as well as displacement current factors. The program is formulated in such a way that it is well suited for computing the EM response for any arbitrary position of the source loop in air or on the surface of the model, in contrast to the earlier methods which face convergence problem for source position on the surface of the model. The program has wide application and is capable of computing the EM response at any arbitrary point either inside or outside the source loop. The validity and accuracy of the program is demonstrated by computing the EM response of a large loop source over the homogeneous and multi-layer earth models. Response curves depict their characteristic variations. The computed results are in coincidence with the published results for the quasi-static region ( f⩽50 kHz) and are extension of their characteristic variation in the non-quasi-static (50 kHz⩽ f⩽1000 kHz) region. Matching of computed results with the published results demonstrate the validity of the program.