Parameter Estimation of a Horizontally Multilayered Soil With a Fast Evaluation of the Apparent Resistivity and its Derivatives

The information of earth structure is curial for designing the grounding system and evaluating the transmission line parameters. In order to obtain the earth structure using the measured data, an efficient algorithm for the parameter estimation of a horizontally multilayered soil by using a novel integration method is proposed. In the proposed algorithm, an adaptive iteration process will terminate till the predefined error reaches the requirement, where the earth parameters, such as the layer depth, layer resistivity, and layer number, are adjusted accordingly with the help of the Levenberg-Marquardt algorithm. In each iteration, the key is to evaluate the apparent resistivity and its partial derivatives with respect to soil parameters, which are expressed in the form of general Sommerfeld integral (GSI). In this paper, the GSI is divided into two parts. The first part with an infinite upper limit is integrated along a novel complex integration path instead of the conventional real axis path, which makes the evaluation of the GSI highly efficient due to the fast damping property of the transformed kernel. The second part with the finite integral interval is calculated using the cubic spline technique to have a semi-analytic expression, which can avoid evaluating the oscillatory kernel. In comparison with the results in the published literatures, numerical examples show that the proposed soil parameters estimation approach can reach good accuracy, and is robust and efficient. The reason is simple as the GSIs are calculated by using the well-designed and sophisticated approach. With extensive numerical experiments, the proposed algorithm is believed to be a capable and applicable candidate in engineering to invert the information of the earth structure.