INTERPRETATION OF RESISTIVITY SOUNDING MEASUREMENTS IN N-LAYER SOIL USING ELECTROSTATIC IMAGES

Geophysical inversion involves the estimation of soil parameters from a set of observations. Multilayer soils are modeled by N horizontal la yers with distinct resistivities and depths. For known soil parameters , the apparent resistivity distribution can be computed efficiently fr om electrostatic images. Since the model responses are generally nonli near functions of the model parameters, least-squared minimization tec hniques prove to be useful for evaluating layer resistivities and dept hs to agree with measurements. This paper demonstrates how electrostat ic images can be combined for increasing efficiency in the computation of apparent resistivities and sensitivity factors such as the first a nd second gradient of the distance with respect to the model parameter s. The factors are then used to solve the more demanding task of resis tivity interpretation of measurements from Wenner, Schlumberger, Dipol e or alternate electrode configurations. Results are presented for two -layer soil and for actual cases with three layer soil.