Quasi3D Inversion of Airborne EM Data

Abstract

Full 3D inversion of AEM data is not generally available to minerals explorers because of limitations in current algorithms and computer resources. Consequently we must resort to approximations to full 3D AEM inversion to support today's exploration projects. One form of approximation is to reduce the dimensionality of the inverse problem from 3D to 1D and while layered earth inversion has proven fast and effective in practice, it has limitations in 3D environments. To address these limitations we propose a physically motivated approximate 3D AEM inversion: Quasi3D inversion. Full 3D EM inversion requires calculation of the 3D induced current in the earth whereas the Quasi3D approximation is based on a full 3D inversion but with a simplified, approximate, induced current flow in the earth. We demonstrate the Quasi3D approximation by comparing its response over the interface of a quarter-space model with the full AEM response, and then demonstrate Quasi3D inversion on a challenging synthetic model and on field data. From our work we conclude that the Quasi3D approximation is an effective and efficient approximation which should aid in the interpretation of AEM data for today's exploration projects.