Large Scale 3D Airborne Electromagnetic Inversion – Recent Technical Improvements.

Abstract

3D airborne electromagnetic (AEM) inversion has routinely been applied to frequency and time-domain problems over the past few years, however this research field continues to undergo rapid improvements with the implementation of new ideas and faster computational resources. To keep pace with these developments, we have rewritten our 3D AEM inversion software suite to leverage the rapid growth in parallel processing, and to create a flexible inversion framework capable of standard inversion plus many additional types: joint, cooperative or parametric, all on semi-structured octree meshes. Our resulting framework further improves recent key ideas such as the decoupling of forward meshes from the inverse mesh, to allow the forward problem to be easily distributed on separate nodes of a cluster for fast and efficient modelling of the fields. We present two large-scale field examples, one in the frequency domain and one in the time domain. The frequency domain survey demonstrates our ability to recover thin conductors, in this case representing orogenic gold targets, across a large region (40km x 35km). The time domain example focuses on a smaller area within a larger survey area where mapping groundwater resources is the primary goal. Here the fine-scale results are compared to a 1D inversion, and we see a good correlation between the 3D and 1D results due to an approximately 1D layered-earth environment. However we see a removal of 1D artifacts in the neighbourhood of vertical conductors and topographic changes in the 3D result with the added bonus of information between lines in which decisions regarding groundwater management can be made.