Detection depth of transient electromagnetic method for A-type layer

First, the diffusion process of transient electromagnetic (TEM) field is simulated by FDTD; then the transient field responses on three typical geo-electrical models are obtained with G-S algorithm, and detection depths corresponding observation time are inversed; lastly, the response curves are transformed to time-frequency (T-F) plane by means of Gabor expansion. The results show that conductive overburden of A-type section has retard effect. To detect the same depth requires longer time there exists the overburden. Since electromagnetic energy will concentrate and consume in the overburden, it is necessary to develop high power transmitter to gain sufficient signal noise ratio for explorations in such area. The results have been approved by practical prospecting in Xutuan, Dongpang, Renluo and Xuzhou.