Estimating the parameters of simple models from two-component on-time airborne electromagnetic data

The horizontal and vertical components of the on-time electromagnetic (EM) response can be used to estimate the parameters of simple models like thin sheets, half-spaces, thin sheets over a lower half-space and a two-layer model. The formulae used in these methods are valid in areas where the on-time response is essentially proportional to the conductivity or conductance, the so called "resistive limit". The half-space and thin-sheet over a lower half-space models can be combined to give an estimate of the conductivity for a lower half-space below a thick sheet that might be reasonable for the whole of the survey area. With this estimation an equation solver can be used to estimate the thickness and conductivity of the overlying thick sheet over the whole survey area. This latter approach seemed most appropriate for the Russell South area in the Athabasca Basin, Canada, where GEOTEM data has been collected. The output of the algorithm was generally stable. Although it did not always reliably reproduce the overburden thicknesses as measured in a set of reference drill holes, it did give an estimate that was reasonable in the relatively conductive areas.