Fast approximate solutions of transient EM response to a target buried beneath a conductive overburden

Abstract

We derive fast transient electromagnetic (TEM) solutions for a thin‐plate conductive target buried in a resistive host rock overlain by thin conductive overburden. For this model, the total TEM field is composed of the overburden response, which is known analytically, and the target response that is approximated by a wire loop. Thus the transient response of the target in free space is approximated with a single exponential function. The interaction between the target and the overburden is approximated by convolving the overburden‐delayed driving field with the exponential function. The target response is then computed from the wire loop by the Biot‐Savart law in free space, thus neglecting the second overburden‐delay effect. Including the second overburden‐delay effect does not yield significantly improved results. The approximate solutions agree reasonably well with scale model and numerical results, but their computation is more than 100 times faster than conventional methods and can be easily done on a small personal computer.