A TRIPLE-GRID TECHNIQUE FOR THE 3D INVERSION OF DC RESISTIVITY DATA INCORPORATING ARBITRARY TOPOGRAPHY

We present a novel technique for the determination of resistivity structures associated with arbitrary surface topography. The approach represents a triple-grid DC resistivity inversion technique which is based on unstructured tetrahedral meshes and a finite element forward operator applied to the secondary potential. We use a Gauss-Newton method with inexact line search to fit the data within error bounds. A global regularization scheme using special smoothness constraints is applied. The regularization parameter compromising data misfit and model roughness is determined by an L-curve method and finally evaluated by the discrepancy principle. A resolution-dependent parameterization helps to keep the inverse problem small to cope with<br>memory limitations of today’s standard PC’s. Thus, the approach can be applied to large-scale 3D problems. As a byproduct of the primary potential calculation we obtain a quantification of the topography effect and the corresponding geometric factors. The latter are used to prevent the reconstruction process from topography induced artifacts. We first test our technique to synthetic data from a burial mound to demonstrate its functionality and efficiency. Then, we apply the method to data gathered on an abandoned mining dump.