The Contrast Research Of Single Loop And “8” Sharped Loop On 1D Modeling And Inversion Of TEM

This paper mainly study on the forward and inversion comparative study of one-dimensional of the single loop and "8" shaped loop.First introduced the research status of the transient electromagnetic method at home and abroad, Mainly includes transient electromagnetic method development process, the forward and inversion development situation, development status and trends of the transient electromagnetic instruments and systems.Secondly, introduce the basic theory and working principle of the transient electromagnetic method.Then the application of Hankel transform and the G-S transform for solving one-dimensional forward problem of the single loop device,and according to the geometrical relationship of the single loop and "8" shaped loop coil, solving the forward problem of the "8" shaped loop with the coordinate transformation method.Finally,using MATLAB programming to get a one-dimensional forward procedure of geoelectric model under two different device, draw the one dimensional forward curves(A, D, G, Q H, K, KH model) of the different model and compare it.The results show: the attenuation shape of forward curves of the single loop and "8" shaped loop is similar, they all have reaction to the formation of the apparent resistivity,the difference is that the forward curve attenuation of "8" shaped loop is faster than the single loop.Comparative study on one-dimensional inversion of these two loop, the first is definition study on the apparent resistivity.According to the results of previous studies, the apparent resistivity is divided into early and late time and all-time apparent resistivity, and explains the advantages and disadvantages of each definition.Studies show that the apparent resistivity of early and late time are only suitable for the apparent resistivity defined under extreme conditions, the majority of the actual situation can’t meet.Only the all-time apparent resistivity can meet the definition in most cases, so this paper adopts the definition of the all-time apparent resistivity in the inversion.Followed by the comparison of the all-time apparent resistivity results calculated by the translation algorithm and the dichotomy, the all-time apparent resistivity calculated by the dichotomy in the late time is more stable.Finally decided to use the dichotomy to calculate the all-time apparent resistivity. Then describes the inversion method,mainly to explain the theory of apparent conductivity inversion and smoke ring inversion,the authors chose the usual smoke ringinversion method.Finally,on the basis of dichotomy, inversion imaging is carried out for different geoelectric model(A, D, G, Q H, K, KH model),draw the inversion curve compare figure of the single loop and the "8" shaped loop, and compared the inversion result of both loop, The results show that: due to the nature of the smoke rings inversion,inversion results of the two devices at formation interface, calculation values of apparent resistivity were distorted; The single loop and the "8" shaped loop in the model fitting degree all are ideal, the difference is that the apparent resistivity calculated by "8"-shaped loop is slightly larger than the single loop.In order to verify the inversion results and to study the differences in the practical application of the single loop and the "8"-shaped loop device, the author carried out the actual measurement of the two kinds of devices in the same area, compare the quality of both datas and the respective data interpretation results.The results show that: The "8" shaped loop in the aspect of anti-jamming ability is better than that of the single loop,apparent resistivity calculated by the "8" shaped loop are slightly larger than the single loop,which verify the theoretical results of the inversion.