Comparing 1D and 2.5D AEM Inversions Using a New Adaptive Inversion Solver in a 3D Geological Mapping Environment

The advantages of 2.5D airborne electromagnetic inversion in 3D geological mapping applications compared to the more commonly used CDI transforms or simple 1D inversions are described using an example from the Bryah Basin in Western Australia. We demonstrate this using a substantially rewritten version of ArjunAir (Wilson et al, 2006), a product of the CSIRO/AMIRA consortium (project P223F). The ArjunAir inversion solver has been replaced with a new GSVD (Paige et al, 1981) solver, with adaptive regularisation which also incorporates a misfit to the reference model and a model smoothness function. The ArjunAir forward modelling code has been revised to fix two errors which manifest at late times around high resistivity discontinuities and in steep topography. We allow the use of a starting or reference geology/resistivity model to influence the inversion. The software has been parallelised using Intel MPI. The software is implemented in a commercial 3D geological modelling package with an intelligent graphical user interface for inversion setup, for introduction of geological reference models and for visualising results. Apparent Resistivity, 2.5D Forward and 1D and 2.5D Inversion methods are integrated in a single 3D geological, electromagnetic and potential field (gravity and magnetics) forward and inverse modelling environment.