Series Expansion-Based Geoelectric Inversion Methodology Used for Geoenvironmental Investigations

Geophysical surveying methods can be effectively used for geoenvironmental site investigation. A review of conventional inversion-based data processing methods is presented. The estimation of geometrical and petrophysical parameters of geophysical models is highly affected by the noise level of observations, the problem of ambiguity and uncertainty of modeling. A reliable high-resolution solution requires the application of advanced inversion methods. Several geoenvironmental studies have shown that the quality of inversion estimates can be greatly improved by the use of joint inversion methods. The series expansion-based inversion method is presented as a joint inversion technique that performs significantly better parameter estimation than conventional inversion methods. The accuracy and reliability of estimated parameters can be improved by increasing the data-to-unknowns (over-determination) ratio of the inverse problem. The conventionally used 1-D (single) inversion method is compared to 1.5-D, un-weighted and weighted 2-D series expansion-based inversion procedures by using direct current geoelectric data. The estimation errors and correlation coefficients of model parameters are calculated to check the quality of inversion results. In this study, field cases demonstrate that at least one order of magnitude improvement of precision in the parameter space can be achieved by the series expansion-based technique. It is also shown that the new inversion methodology is applicable to give an estimate of high spatial resolution for laterally inhomogeneous formations with rapidly varying rock interfaces