3D inversion of frequency-domain AEM surveys with a moving footprint

We show that it is practical to invert entire airborne electromagnetic (AEM) surveys to 3D conductivity models with hundreds of thousands of cells within a day on a workstation. We have exploited the fact that the area of the footprint of an AEM system is significantly smaller than the area of an AEM survey to develop a robust 3D inversion method which uses a moving footprint. Our implementation is based on the 3D integral equation method for computing AEM data and sensitivities, and the re-weighted regularized conjugate gradient method is used to minimize the objective functional. Even for terranes which are arguably as close to 1D as geologically possible, we demonstrate that results from our 3D inversion are a significant improvement over those models obtained from layered earth inversion. We demonstrate this with 3D inversion of RESOLVE frequency-domain AEM data acquired for salinity mapping over the Bookpurnong Irrigation District in South Australia.