Analyzing the Effect of the Near-Surface Inhomogeneity on Three-Dimensional Resistivity Models

The impact of Near-Surface Inhomogeneity (NSI) on three-dimenssional (3D) resistivity data has been investigated using four electrode arrays. These arrays are Dipole-Dipole, Pole-Dipole, Pole-Pole, and Wenner arrays. Two 3D numerical models were designed by an 11m x 11m survey grid with 1m electrode spacing, featuring a low-resistivity main target and two NSI features with high resistivity of 100Ωm and low resistivity of 10Ωm, respectively. The results indicate that all arrays can detect the NSI features with enhanced performance when the low-resistivity NSI feature is presented. The high-resistivity NSI feature creates a saw-tooth form, while the low-resistivity NSI feature generates anomalous features. The Dipole-Dipole array demonstrates superior performance in delineating both NSI features, accurately detecting its lower boundary, and approximating resistivity. Pole-Dipole shows good boundary detection but with a slightly lower resolution. Pole-Pole and Wenner arrays exhibit the lowest resolution. They are overestimating the lower boundary of both NSI features. All arrays display artifacts due to the NSI effect, except for Pole-Pole, whose too-thick depth slice prevents that. For the primary target detection, Pole-Dipole and Dipole-Dipole arrays perform best resolution, allowing to delineate it at approximately the exact depth and form with resistivity values very close to the actual resistivity of the primary target. In terms of misfit errors, Dipole-Dipole and Pole-Dipole arrays offer superior resolution and performance despite their relatively high misfit errors. This analysis provides insights for selecting appropriate arrays in complex near-surface conditions.