Abstract:  The shortoffset transient electromagnetic method (SOTEM) is an effective tool for mineral resource exploration in mountainous areas. However, the topography has a serious effect on the survey, which brings great difficulties to the fine interpretation of transient electromagnetic data.  We analyzed the influence characteristics of terrain on SOTEM data based on the 3D unstructured timedomain finiteelement method. By using unstructured mesh to match the rugged  terrain, the SOTEM responses  on a complex geological model  were quickly simulated by combining the edge finiteelement method and backwardEuler scheme，and the spatial distribution characteristics of the 3D topographic responses were obtained based on the simulation of a large number of typical terrain models such as hills and valleys. The results show that topography has serious influence on SOTEM response, and the law is very complex. On this basis, we further analyzed the influence of complex topography on the detection of underground targets. It is found that the coupling of complex topography and underground anomaly   makes it impossble to effectively distinguish underground targets, which brings great difficulties to the accurate detection of underground targets.

Key words: shortoffset transient electromagnetic method, grounded source, topography, 3D unstructured edge finiteelement method