The Shielding Effect of Low Resistivity Layer in TEM

Transient electromagnetic method can penetrate high-resistivity shielding layer and delineate underlying strata or structure. However, the shielding effects of low-resistivity layer on transient electromagnetic exploration are often ignored, especially for low-resistive overburden. It is of great importance to ensure exploration depth and improve detection precision by researching the relationship between low-resistive layer and electromagnetic field. In this paper, the propagation process of the subsurface and surface TEM field responses were simulated using finite-difference time-domain method (FDTD). And the characteristic response of low-resistivity overburden was studied using numerical modeling. The observation time with low-resistivity layer was estimated using observation time formula. It was shown that a low-resistivity layer will not only reduce the propagation speed of the field, but also weaken the response of low-resistivity target.