![]() 4) should give the most accurate results. ![]() Since all geological structures tend to be three-dimensional (3-D) in nature, a 3-D resistivity survey and interpretation model (Fig. A two-dimensional (2-D) survey and interpretation model is required for more accurate results. The greatest limitation of this method is that it does not take into account lateral changes in the subsurface resistivity which can result in errors in the interpreted resistivity and thicknesses of the layers. The resistivity sounding method has been used for many years, particularly in groundwater exploration. A detailed description on the use of the iterative damped least-squares method for the inversion of resistivity sounding data is given by Inman ( 1975). Starting from an initial model (such as a homogeneous earth model), this method iteratively refines the model so as to reduce the data misfit (Fig. λ is a regularization factor that stabilizes the ill-conditioned Jacobian matrix usually encountered for geophysical problems ( inverse theory, singular value decomposition). J is the Jacobian matrix of partial derivatives of apparent resistivity with respect to the model parameters. ![]() Here, the model parameters are the logarithms of the resistivity and thickness of the model layers. Where the data misfit vector Δ g contains the difference between the logarithms of the measured and the calculated apparent resistivity values and Δ q is a vector consisting of the deviation of the estimated model parameters from the true model. It has now become one of the standard geophysical exploration techniques widely used in environmental, engineering, hydrogeological, and mining investigations (Loke et al. ![]() Over the past 25 years, the resistivity method has undergone rapid developments in instrumentation, field survey techniques, data interpretation, and novel applications in the geosciences. The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity, and degree of water saturation in the rock ( electrical properties of rocks). The true subsurface resistivity can be estimated by making the measurements of potential difference at different positions of the current and potential electrodes, converting these values into apparent resistivity and then inverting the data set. An electric current is injected into the ground through two electrodes, and the voltage difference is measured between two other electrodes (Fig. Electrical resistivity surveys map the subsurface structures by making electrical measurements near the ground surface. ![]()
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