Estimating overburden thickness in resistive areas from on-time airborne em data

Abstract

We propose a method to invert two-component time-domain EM data to a thick-sheet over half-space model, as a solution representing an overburden on top of bedrock. We first estimated the conductivity of the lower half-space using a combination of inversion for half-space (if appropriate) or a thin sheet over half-space (also when appropriate). This yielded a number of estimates, which could be combined to give a reasonable estimate of the lower half-space conductivity for the survey area. With this estimation an equation solver was used to solve the thick-sheet over half-space model for sheet thickness and sheet conductivity. The output of the algorithm was generally stable when applied to GEOTEM data in an area of moderately resistive overburden over a generally more resistive half-space. Although it did not reliably reproduce the overburden thicknesses as measured in the reference drill holes, it did give an estimate that was reasonable in the conductive areas.