Topographic Effect In CSAMT & Compare Of Terrain Correction Methods

The topographic effects on the apparent resistivity response of the controlled-source audio frequency telluric electromagnetic (CSAMT) survey have been systemically studied by numerical simulation, also the comparison & application of the terrain correction or inversion methods.First, based on the theory of the CSAMT and Finite Element Method (FEM), both of the models of irregular terrain (ridge, valley, and slope) and containing variant anomaly body under the irregular terrain have been simulated. Results show that terrain effect is very serious where undulate angle is more than 10 degree, and at the different condition, the effect is different. Sometimes topographic effect can cause mistake or falsity explanation, especially at the TM mode.Then, by comparing of a few different terrain correction or inversion methods, we have found that 1D & and 2D flat land inversion can not remove the topographic effect; space filter can remove small unhomogenous; the ratio (terrain correction factors) technique can preferably remove the topographic effect, where terrain undulate is not serious; rough topography 2D inversion can remove the topographic effect perfectly, and can give good image of subsurface resistivity model.After then, we present a practical archaeological exploration case of 2D terrain correction in CSAMT survey by choosing the useful correct method. The results show that terrain corrections can greatly attenuate the topographic effects and improve the quality of data interpretation.Lastly, an error expression is derived for calculating the Cagniard apparent resistivity error caused by magnetic sensor declination in CSAMT survey.