Inversion of the Wideband and High Frequency Electromagnetic Data

To estimate the underground resistivity and permittivity, the nonlinear least-squares inverse method based on Monte-Carlo algorithms is applied in this paper to invert the ellipse polarization data of wideband highfrequency electromagnetic (WHFEM) field. The inversion case study indicates that the nonlinear least-squares inversion method can work well in the half-space or two-layer earth. In order to reduce instability and increase convergence speed, the Monte-Carlo algorithm is used for multiple layers model. In the second part, we also adopt the phasor vectorgraph method for fast inversion of apparent resistivity and permittivity which is helpful to geology mapping and constructing the initial model for the least-squares inversion.