Topographic effects and correction methods of loop source TEM in mountainous exploration

Transient electromagnetic exploration in Huangling, Shaanxi Province and Wangjialing, Shanxi with large loop source and in Zhongtiaoshan Mount, Shanxi Province with small loop shows different features. The character of effects can be judged through channel chart based on the classical topographical effect regularities. Different behaviors of topographic effect have been interpreted according to the mechanism of gathering and dispersion of current lines. For typical topographic effect, general correction methods, such as ration correction, filtering correction, could be used, for non typical topographic effect of large loop it is suitable to remove the parts that had been occupied by air in apparent resistivity-depth section and elevation correction of observation points is enough for small loop which has less effect by topography.