Numerical Calculation of Diffusion Depth and Skin Depth Based on a GEMTIP Model in Electromagnetic Sounding Methods

Electromagnetic (EM) sounding methods in the time and frequency domains are widely used in polymetallic ore exploration and can measure both EM induction and induced polarization (IP) responses simultaneously. Depth inversion is a crucial factor affecting the accuracy of data interpretation. The effect of IP on EM wave propagation has been ignored in traditional studies of diffusion depth and skin depth. This article is based on the generalized effective-medium theory of the IP effect (GEMTIP) model to represent the IP effect. The frequency domain solution based on GEMTIP is obtained. To address the problem whereby the time-domain solution cannot be solved by inverse Laplace transform, rational approximation and linear programming methods are used to simulate the variation of pulse field source with time and distance. We analyze the influences of geometrical parameters and physical properties of rocks and ores with the IP effect on the depth. Finally, we consider the influence of intrinsic chargeability and improve the classic diffusion depth formula. The formulae for estimating the time-domain diffusion depth of the IP effect under certain conditions are given and verified. These methods are of great significance to better understand the relationship between the subsurface dispersive media and the propagation of EM waves.