Staggered grid inversion of cross hole 2-D resistivity tomography

We apply the staggered grid method (referred to as SGERT in this paper) to the inversion of electrical resistivity 16 data in order tominimize ambiguity and smearingwhen inverting a datasetwith a unique grid. Artefacts are typ- 17 ical drawbacks in inversion of cross-hole resistivity data, especially in the zones of the image characterized by 18 poorer model resolution, in presence of noisy data or when sound a-priori information is poor or not available. 19 SGERT is based on a reiterated inversion of the same resistivity dataset on a series of grids obtained by staggering 20 a starting one. The application of the SGERT tends to limit the formation of artefacts, as it roughly operates as a 21 moving average. Moreover, the SGERT permits to estimate the standard deviation of each resistivity value 22 (pixel) in the resulting image. This datum improves the quantitative information of the inverted resistivity 23 image.We run a set of tests applying SGERT to the inversion of 2-D synthetic electrical resistivity data comparing 24 the final results to the ones obtained using a standard single grid inversion. The SGERT reveals a reduction of ar- 25 tefacts, and shows amore robust reconstruction of the syntheticmodel.We also apply the SGERT to a cross-hole 26 resistivity field dataset collected for characterizing and monitoring a contaminated site.