2.5D inversion of airborne electromagnetic data

Abstract

2.5D electromagnetic (EM) modelling computes the response of a 3D source from an arbitrary 2D geoelectrical model. As such, it is practical for airborne EM (AEM) data to be inverted using 2.5D modelling provided that the geoelectrical cross-section is relatively constant along a strike length that exceeds the AEM system footprint. The program ArjunAir is introduced for modelling and inversion based on a 2D finite-element method that enables the accurate simulation of 3D source excitation for full domain models inclusive of topography, non-conforming boundaries, and very high resistivity contrasts. Inversion is based on an iterative Gauss-Newton method that is solved using the damped eigenparameter algorithm. Examples are presented for synthetic and practical frequency and time-domain AEM surveys for which inversion run-times are on the order of hours.