摘要
The apparent resistivity tensor pB is an electromagnetic transfer function,which can be used to analyze and explain the underground electrical structure.Conventional method for obtaining the parameter requires controlled sources and can be easy to be disturbed by cultural noises.We present a new method for calculating the apparent resistivity tensor,the current density is first obtained by measuring the curl operator of the magnetic field on the Earth's surface.This approach is independent of the assumption of a plane wave,and may be used irrespective of source types and field areas.We derived the analytical expressions of the apparent resistivity tensor based on synthetic horizontally layered models with a vertical magnetic dipole source.We then calculate the responses of Pb through numerical modeling examples using both natural sources and controlled sources.Compared to traditional apparent resistivity definitions,our apparent resistivity tensor has the same amplitude value but with more sensitive phases in the far zone,and shows few distortions in the transition zone.And in the near-field zone,it is closer to the resistivity distribution under the ground.The simulation results have demonstrated the effectiveness of the proposed method for calculating the apparent resistivity tensor.
