Approximate 2D inversion of AEM data

Abstract

Airborne electromagnetic (AEM) data are presently inverted with one-dimensional (1D) models, either as Conductivity Depth Images (CDI) or with full non-linear inversion, to build model sections from concatenated 1D models. If lateral conductivity changes are small, 1D models are justified. However, AEM investigations are often carried out specifically to find localized conductors, and in this case, 1D inversion is inadequate and will often produce artefacts in the model section. We have developed an approximate two-dimensional (2D) inversion method that deals with laterally inhomogeneous sections. The method is based on the adaptive Born approximation previously applied by one of the authors (NBC) to the interpretation of central-loop ground EM profiles. The technique produces synthetic models with moderate conductivity contrasts and with some improvement over CDI sections. The computing speed is comparable to that of stitched 1D inversions. An example of processing field data with the approximate 2D inversion method over a massive nickel sulphide deposit shows results that are promising for its routine application on large AEM data sets.