Tomographic pseudo-inversion of resistivity profiles

Abstract

A new approach to construct vertical and/or horizontal pseudosections starting from sets of resistivity (and/or IP) data is presented. In principle it consists in the division of the subsoil into a number of pixels (discretization), arranged in a 3D halfspace. The resistivity of each pixel is then obtained by a back-projection of the set of acquired experimental data, that is by arranging a set of convolutions using 3D filters. The coefficients of the filters are calculated, depending on the geometry of the electrode array used, on the basis of a mask reproducing the «influence coefficients» of all the pixels. The aim of these representations is to match the shape of the investigated structures as close as possible, so that, even if it can be considered a fast arrangement of the experimental data rather than a real inversion, it can be a useful tool in interpretation, at least as a simple preliminary sketch. This method is discussed, focussing on some critical choices regarding the construction of the filters and the use of smoothing factors; some applications on synthetic data calculated on simple models of buried resistive spheres are also presented.