Modeling of rugged topography distortions in ground TEM surveys for grounded-wire and loop source configurations

Abstract The transient electromagnetic (TEM) method is extensively applied in engineering and resource exploration. However, most theoretical studies assume a flat surface, which fails to represent the complexity of real-world topography. In field conditions, rugged topography alters the transmitter geometry, distorting the response and reducing detection accuracy. Grounded-wire and loop sources are both common in ground TEM surveys, yet their distinct geometric and electromagnetic characteristics lead to fundamentally different interactions with rugged topography. A comparative study is therefore essential to understand and correct these distortions, a critical step toward improving data interpretation accuracy in geologically complex areas. We employ an unstructured finite-element method to perform 3D numerical modeling for representative monoclinal slope and mountain-valley models. Our results show that rugged topography significantly affects the dBz/dt responses of both source types, particularly during early times, with effects diminishing later. Focusing on a mountainous model with a grounded-wire source, we further analyze the influence of key parameters such as offset distance, source length, and topographic elevation. The results indicate that varying offset distance and source length does not significantly mitigate topographic effects, whereas greater topographic elevation intensifies them. To reduce these distortions, we implement and evaluate two topographic correction methods, confirming that both techniques effectively eliminate the influence of rugged topography for their respective source configurations.