Staggered grid inversion of cross hole 2-D resistivity tomography

Abstract

Abstract We apply the staggered grid method (referred to as SGERT in this paper) to the inversion of electrical resistivity data in order to minimize ambiguity and smearing when inverting a dataset with a unique grid. Artefacts are typical drawbacks in inversion of cross-hole resistivity data, especially in the zones of the image characterized by poorer model resolution, in presence of noisy data or when sound a-priori information is poor or not available. SGERT is based on a reiterated inversion of the same resistivity dataset on a series of grids obtained by staggering a starting one. The application of the SGERT tends to limit the formation of artefacts, as it roughly operates as a moving average. Moreover, the SGERT permits to estimate the standard deviation of each resistivity value (pixel) in the resulting image. This datum improves the quantitative information of the inverted resistivity image. We run a set of tests applying SGERT to the inversion of 2-D synthetic electrical resistivity data comparing the final results to the ones obtained using a standard single grid inversion. The SGERT reveals a reduction of artefacts, and shows a more robust reconstruction of the synthetic model. We also apply the SGERT to a cross-hole resistivity field dataset collected for characterizing and monitoring a contaminated site.