A Study About1D Forward And Inversion Algorithm Of Rectangular Loop TEM

Transient Electromagnetic Method is also known as Time DomainElectromagnetic Method, It’s a kind of electromagnetic detection method of artificialsource that based on the principle of electromagnetic induction, based on the process oftransmitting the primary electromagnetic impulse to underground with ungroundedloop or ground source and analyzing changes of secondary field versus time to get theelectrical characters of the medium. This method is purely secondary field observations,high-resolution, large depth exploration, now widely used in various fields ofgeological exploration. This paper first discusses the transient electromagnetic methodof research progress, equipment, and principle of the method data acquisition-processing-interpretation, this paper derived the frequency-domain and time-domainelectromagnetic transient expression of the circular frame. Use of reciprocity and roundframe response expressions, the paper deduced the rectangle transient electromagneticresponse expressions, Its analytical expression is a double integral: the inner integral ishankel type integral, the outer integral is the cosine integral. In this paper, aftercomparing several filtering algorithm, I use47-point GS filtering algorithm and cosinefiltering algorithms to complete a forward calculation.In modeling the basis of the study, we using the above modeling method ofnumerical calculation method to write the Rectangle-loop transient electromagnetic1Dmodeling procedures, and make a lot of forward modeling, this paper analyzeshomogenous half space transient response characteristics about the differenttransmitting current, different transmitting line box and different fields of the earthresistivity, the results show that with the increase of the current, the amplitude of theelectromagnetic response linear increases; the transmitting line box bigger, the transientresponse of the slower decay, and the early time longer; in the even half space condition,the resistance of the higher rate of strata, the transient response of the late into theearlier; formation resistivity is lower, the transient response to the late is later. Inaddition, we did many other1D forward model such as the two layers of D,G electricmodel, three layers of Q, A, H, K electric model, hen analyze the modeling of the curve form and did a lot of contrast tests, it have a good guide to TEM data processing andinterpretation.Based on the1D forward modeling, this paper gives a brief summarizes of thegeophysics inversion methods and focus on the smoke theory inversion and the theoryof Occam’s inversion. The results show that when processing TEM data,the smoketheory inversion should be use at first for qualitative analysis, then on the basis ofqualitative analysis the iterative should be adopted for quantitative analysis. The modelstudies here use Occam’s inversion method which solves the regularized problem bysearching for the smoothest model that fits the data. The utility of this method is that itgenerally produces smooth peaks in the model that correspond to features that are wellconstrained by the data, whereas features not constrained by the data will be smoothedover or entirely absent in the model.