关键词: 时间域航空电磁法, 深切割地形, 有限体积法, 八叉树网格, 三维正演

Abstract:  Currently, the exploration potential for mineral resources in China’s plains and gently undulating hilly areas is relatively limited. Future prospective areas for mineral exploration are mainly distributed in the deeply incised, high-altitude regions of western China. These areas are characterized by rugged topography, challenging accessibility, and sensitive ecosystems, which impose significant constraints on the implementation of traditional ground-based geophysical exploration methods. As an efficient geophysical detection technique, the time-domain airborne electromagnetic (TDEM) method holds great application value for mineral exploration in deeply incised complex terrain. This study conducts three-dimensional forward modeling research for TDEM surveys based on the finite volume method and octree mesh technology. The correctness of the forward algorithm is first verified using a half-space model. Ridge and valley terrain models are constructed to compare and analyze the differences in electromagnetic responses under different flight modes. Furthermore, by embedding low-resistivity anomalous bodies beneath undulating terrain, the coupling mechanism between topographic effects and ore body responses is investigated. Finally, the method is performed to forward modeling based on an actual geological profile from the Xiarihamu area. The research demonstrates that in areas with steep terrain such as ridges and valleys, the early-time responses are generally enhanced, while the late-time responses significantly decrease at ridge tops and increase markedly at valley bottoms, revealing characteristic terrain-induced distortions. Additionally, topography causes complex multi-faceted distortions in the responses of mineralized anomalous bodies: early-time and late-time responses may be obscured by terrain-induced distortions, but the variations caused by the anomalous bodies remain identifiable during the mid-time response stage. Lastly, the modeling results from the real geological profile verify the practicality of this method in deeply incised terrain and complex geological conditions, providing reliable theoretical support for three-dimensional inversion of TDEM data.

Key words: time-domain airborne electromagnetic method, deeply incised terrain, finite volume method, octree mesh, three-dimensional forward modeling ,