Three-Dimensional Soil Resistivity Inversion Using Patching Method.

To apply Electrical Resistivity Tomography (ERT) in monitoring temporal and spatial variation of soil water, by using finite-element method as forward modeling, we proposed a patching algorithm of inversely calculating 3D soil resistivity in this paper. From finite-element forward modeling, sensitivity calculation to formation of initial model parameters, we systematically described the inversion calculation process of using patching algorithm. At the end, we gave out results about two numerical experiments and one field measured data inversion to illustrate the effectiveness of the algorithm. By patching algorithm, the initial soil resistivity model is step by step modified to make the calculated potential approximate that measured. Each measurement event (group of pole-pole array measurements which have same current electrode and input current) composes a step of modification to the model. This algorithm is appropriate when the data number for one measurement event is quite less than the parameter number of the model and the measurement event number varies with the equipment capacity or prospecting objectives, and even when the resistivity changes with time. Numerical experiments and field measured data inversion indicated the effectiveness of the inverse algorithm, but also revealed the difficulty of completely inversely calculating out the 3D subsurface soil resistivity only by using the data measured at the soil surface.