Direct inversion of time‐domain electromagnetic data

Abstract

This note describes a simple method for converting transient electromagnetic (EM) sounding data into profiles of conductivity versus depth, based on an approximate image representation for the decaying induced ground currents. The method can provide one‐dimensional (1-D) inversion for any kind of time‐domain EM sounding data; the discussion here is limited to the case of central‐loop sounding. In particular, I apply the inversion to some time‐derivative central‐loop sounding data and demonstrate that essentially the same interpretation of the geoelectric section is obtained with the simple image method as is obtained using traditional iterative least‐squares fitting to layered models. This simple inverse can be computed much more quickly than an iterative least‐squares inverse, making it possible to estimate the geoelectric section concomitant with data acquisition.