Inversion of soil resistivity by using CSAMT method

Abstract

Accurate soil resistivity information is an important data for designing grounding system. Due to the complexity of the geological structure, we need use various measurement and inversion methods to obtain the soil resistivity. In this paper, the soil resistivity information of stratified media is measured by using the controlled source audio frequency magnetotelluric method (CSAMT). The theory and measurement method of CSAMT are introduced firstly in this paper. According to the Cagniard apparent resistivity information, we can obtain the soil resistivity and depth information of stratified media by using some inversion method. This paper takes the results of bostick inversion as the initial model, and the optimal inversion uses the smooth constrained least square inversion method. There is no data optimization process in bostick inversion method, so its accuracy is not high. But this inversion method can better reflect the basic characteristics of geoelectric section, and can provide a reliable initial model for the accurate inversion of CSAMT data. Based on the results of bostick inversion method, the smooth constrained least square inversion method is used to get more accurate soil resistivity information. Finally, two layer model and three layer model are taken as examples. The results show that the inversion results can match well with the selected model. It can provide an accurate soil resistivity information by using this method in this paper. This inversion method also has many applications in power system, such as calculating the transmission line impedance.