Rectangular Large Fixed Source Device Loop Transient Electromagnetic Method 1 D Forward Modeling Research

Transient electromagnetic method that sometimes is also known as time-domainelectromagnetic method makes use of ungrounded loop or ground line source for launchingpulsed magnetic field to the underground. During the intermittent time of pulsed magneticfield, the coil or grounding electrode is used to observe the secondary induced eddy currentfield caused by the underground media. Thus underground geological structure is detected.Compared with the same point device, the large rectangular loop which is one of TEMcommonly used device has features of optimal coupling with the target body, largeranomalous amplitude, simple form, and smaller flanking geological body impact.This paper firstly describes the exploration works and common working device ofTEM, and then introduces research status of TEM from forward modeling, apparentresistivity and instruments, and briefly discusses the development trend of TEM.Secondly, TEM is used to detail derive the process of electromagnetic response overuniform and layered media. The TEM response expression of uniform media is integralexpression of probability, and the expression is the integral of Bessel function of layeredmedia. When the receiver point is zero offset, linear digital filtering method is used forsolving TEM response. And when the receiver point is non-zero offset, poly-lineapproximation method and the sine or cosine transform method are used. Then, Faraday’slaw of electromagnetic induction is used to calculate secondary field induced voltage.Finally, Matlab software is used for curve simulation and comparison over four models. Ithas guide significance to the TEM data processing and interpretation.Thirdly, in terms of apparent resistivity, the period of early, middle and late isdelimited for rectangular loop. And the apparent resistivity expressions of early and lateperiod are computed. Finally, late apparent resistivity is simulated and compared overuniform and layered media.Finally, reatem software is used in terms of the process of real data, and thecomparison of apparent resistivity for real data is required. Then the draw of contour mapneeds to call the surfer software. It plays a supporting role for the qualitative interpretationof large rectangular loop.