Simplified prediction of transient electromagnetic response

Abstract

In general the target response to an electromagnetic system is a complex function of target geometry and of the geometrical and electrical parameters of the apparatus used to make the measurements. Thus, the prediction of system performance is usually done with respect to a particular target. Under some circumstances, however, one can predict the effect of changing one of the system parameters by assuming that the typical conductor in a given area is well represented by a shorted single‐turn loop. This simple, classical concept is shown to be valid for evaluating the effect of primary pulse width on target response to the Input airborne electromagnetic system. The justification of our basic technique for predicting this aspect of AEM system performance is provided by the analysis of Input surveys done in two areas of the Precambrian Shield in Canada. Repeat surveys were done in each area with a 1 ms and a 2 ms primary pulse width. The change in system performance that could be expected by doubling the pulse width was correctly predicted after an analysis of the 1 ms data.