2-D and 3-D tools for electrical imaging in environmental applications

The work presented in this thesis is focused on the characterization of contaminated sites via the application of non-invasive methods, such as electrical resistivity and electromagnetic techniques. With the aim of improving the relationships between geophysical parameters and hydro-geological features of the subsoil, some innovative methods are proposed. In particular, being electrical resistivity tomography an ill-posed and under-determined problem, the solution is computed by an over-parameterization of the model element with respect of the available measured data. The need to improve the resolution of resistivity imaging technique without stressing the intrinsic under-determination of the geo-electrical problem, and to provide more robust results in integrated characterization approaches, guided the work presented in this thesis to works on both “static” 2-D and 3-D problems, and on the inversion of time-lapse data. In addition, joint characterization of contaminated site has been carried out together with chemico-physical and biological analysis. Grid manipulation techniques have been explored and adapted to the inversion of geo-electrical data, in order to solve inversion of resistivity data set trying to improve space resolution without decaying the robustness of the inversion process. Furthermore, results obtained by the testing of a novel code for the inversion of complex resistivity data are presented. The software was implemented on the basis of the Primal-Dual method, which allows flexibility in choosing to minimize the L1- or the L2- norm on both the data and regularization term of the objective function. Strategies related to the inversion of electrical resistivity and IP data have been developed with the aim of improving the interpretability of the results both in space and in time. These activity are part of a common effort for achieving an integrated characterization of contaminated sites, jointly with chemico-physical analysis of soils and groundwater and with measures of presence and degradation activity of hydrocarbon-degrading biomass.