Otze – Airborne EM Inversion on Unstructured Model Grids

Abstract

An efficient, accurate, multi-grid algorithm has been implemented for the modeling of airborne, land, and marine controlled source electromagnetic data, providing accurate 3D depth inversions of frequency and time domain data with cost-effective compute timelines. This is achieved by decoupling the inversion grid from the modeling grid used in the finite difference simulation of the fields. The approach helps also when inverting data from different methods jointly. The model grid consists of columns of prisms that can be arbitrarily dimensioned. This helps to discretize in particular the topography and other interfaces without densely discretizing the upper part of the resistivity model. By setting the horizontal smoothing accordingly, the general geological setting of the survey area can be easily taken into account. Depending on the specifics of the implementation, other structural information will impact the chosen discretization.