Differential evolution-based one-dimensional inversion of whole-zone apparent resistivity for AB-H_z ground-airborne electromagnetic frequency sounding

This study investigated methods for the calculation and one-dimensional (1D) inversion of whole-zone apparent resistivity using the AB-Hz ground-airborne electromagnetic frequency sounding method. The purpose is to improve the accuracy and efficiency of electromagnetic frequency sounding and provide technical support for the high-efficiency exploration of deep subsurface resources. The AB-Hz ground-airborne electromagnetic frequency sounding method enables subsurface detection by exciting an electromagnetic field using a ground electric dipole source AB and measuring the vertical component Hz via unmanned aerial vehicle (UAV)-based observations. This study investigated the characteristics of frequency sounding curves of the whole-zone apparent resistivity under different transmitter-receiver distances. Two iterative calculation methods were established for the whole-zone apparent resistivity of the AB-Hz ground-airborne electromagnetic frequency sounding using the analytical expression of the Hz component of the electromagnetic field generated by a horizontal electric dipole (HED) source. Based on the equivalent resistivity principle, the correctness of the two methods was verified by calculating the H- and K-type geoelectric models using the dual-frequency method. To achieve the multi-parameter nonlinear optimization in 1D inversion, this study introduced an improved differential evolution algorithm and proposed a four-step mutation method to enhance the influence of the optimal solution. These efforts contributed to enhanced global optimization performance. Numerical simulation results show that the inversion results were close to the true values of the models, with a high goodness of fit, verifying the effectiveness of the proposed inversion method. The AB-Hz electromagnetic frequency sounding method exhibited pronounced responses to both low- and high-resistivity target geobodies, with larger transmitter-receiver distance corresponding to more distinct responses to targets. The proposed method can provide a technical solution for exploring inaccessible areas, such as deeply incised mountainous areas.