Conductivity information in three dimensions

Abstract

Airborne electromagnetic (AEM) survey data are traditionally presented as images of EM response, apparent conductivities, or apparent conductances at different delay times. Advances in control of system geometry and waveform monitoring, as well as increases in computing power, now makes it feasible to implement more rigorous processing algorithms. This paper discusses the application of layered-earth inversion to model subsurface conductivity structure from AEM data acquired with the QUESTEM-100sw system. Statistical methods are used to decide which parameters and data to include in a layered-earth inversion. Results show that the optimum number of layers is three and that it is preferable to model relative decay values (with respect to the last channel) than absolute values. Inversion results are presented as a regolith thickness map, bedrock topography map, conductivity depth sections and conductivity-depth slices. These maps, inverted sections, depth slices and profile data can be imported into a geographic information system (GIS) allowing the interactive overlay on, and integration with, other relevant data. Modelling entire QUESTEM-100sw surveys with layered-earth inversions provides the interpreting geologist with conductivity variations in three dimensions.