Automatic estimation of EM parameters in tau-domain

Abstract

Decomposition of transient electromagnetic (TEM) data to a set of exponential basis functions (the t-domain) is an essential step for some fast interpretation methods. Traditionally,the parameters in the t-domain, namely the time constants t, their corresponding amplitudes, and the number of t's have been determined via trial-and-error. In this paper, all these parameters are automatically extracted from TEM data by using the matrix pencil method (MPM) based upon the representation of a sum of complex exponentials. The MPM has been shown to be very robust and efficient computationally. For typical TEM data with about 20 channels, the transient responses have been reproduced with half a dozen exponentials within an RMS error of less than 5%. A by-product of this study is that three other representations of a transient are formulated in order to cover wider dynamic ranges of both responses and sampled times, which are likely to fit the data within much less fitting error. However, determination of the geometric and geoelectric parameters of the target in the ground from the natural frequencies, another inherent parameter related to time constants and estimated from the decomposition of the complex exponentials, remains an interesting and challenging task.