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Study about 1D Forward and Inversion Algorithm of Centrl Loop Transient Electromagnetic Method

Author: GuoZuoWei
Tutor: WangXuBen
School: Chengdu University of Technology
Course: Earth Exploration and Information Technology
Keywords: Central loop Fast Hankel transformation Cosine Transform Region apparent resistivity Smoke ring inversion
CLC: P631.325
Type: Master's thesis
Year: 2010
Downloads: 300
Quote: 3
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Abstract


Transient Electromagnetic Method (Transient Electromagnetic Method, TEM), sometimes also known as time domain electromagnetic (TDEM). It is not grounded return line or ground line source to the underground transmission time pulse magnetic field, the variation over time to detect the electrical resistance of the medium through the secondary eddy current field for observation and study. The method is off primary field observation of pure secondary field, with the advantages of high resolution, great depth exploration, is widely used in the fields of energy, mineral resources, hydrology, engineering, environmental, geophysical methods. This paper first reviews the development course of the transient electromagnetic method, a brief introduction to the characteristics of the transient electromagnetic method, device type and method theory and instruments paper introduces the development status quo and development trend. Forward computation aspects. Maxwell's equations using the transformation to the frequency domain to derive the formula of the central loop transient response of the device. In view of the transient electromagnetic detection usually a step wave, and transient response of the real part and the imaginary part of the parity, simplification transient response formula the forward calculation formula, including two key steps: Hankel transform, cosine transformation. Hankel transform, the comparative analysis of Anderson linear the digital filter 波法汉克尔 transform, and Guptasarma and Singh the linear numerical the filter Bohankeer transform calculation accuracy and computational speed proved in the central loop transient electromagnetic Weizheng calculate high precision to play in Guptasarma and Singh linear numerical the filter Bohankeer transform of computing speed, it is worth using; cosine transform, the paper comparative analysis of the the polyline approximation method cosine transform and digital filtering method Cosine Transform polyline approximation method to select a different the case of frequency points, and different bandwidth, the calculation accuracy, speed done a detailed analysis; contrast, the same accuracy, the the numerical filtering cosine transform calculation speed significantly better than the polyline approximation law cosine transform, and numerical filtering is recommended Cosine Transform. Using the forward numerical algorithm, the preparation of the central loop transient electromagnetic one-dimensional forward modeling program, and a large number of model simulations, including D, G, A, H, K, Q-type ground model, in addition to the use of a dimensional forward to do the proposed two-dimensional forward modeling. Analysis of the forward curve shape, a lot of comparison tests, processing and interpretation of transient electromagnetic guidance. Apparent resistivity. The conventional central loop transient electromagnetic apparent resistivity is defined generally early and late. Region apparent resistivity definition, the paper gives the magnetic field strength, the induced electromotive force method and region apparent resistivity translation algorithm three definitions. Found that the induced electromotive force law and translation algorithm curve completely overlap, and gives the reasons of the curves overlap. The comparative analysis of several region apparent resistivity of the thin layer of low resistivity thin-layer, high impedance reflect the sensitivity of the situation, low resistance, high resistance. Prove transient electromagnetic response of the low resistivity layer responsive, high impedance layer reflects general. In addition, there are false anomaly analysis, given the characteristics of the false anomaly region apparent resistivity of the induced electromotive force method, which will help the region apparent resistivity correct transient electromagnetic data explanation. The Inversion aspects. The smoke ring inversion for transient electromagnetic apparent resistivity a deep conversion method proposed smoke ring inversion region apparent resistivity through comparative analysis of several region apparent resistivity smoke ring inversion proved smoke The circle inversion anomaly reflects superior to the region apparent resistivity. Optimized inversion selected damped least squares inversion of several typical geoelectric model inversion. After a comparative analysis, it is recommended that the integrated use of the above two methods, to smoke ring inversion as a rapid inversion and qualitative interpretation; damped least squares inversion smoke ring inversion results as the initial model, do fine inversion test to prove the two methods combined can not only improve the computational efficiency of the inversion calculation results are closer to the model.

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CLC: > Astronomy,Earth Sciences > Geology > Geology, mineral prospecting and exploration > Geophysical exploration > Electrical prospecting > Method > Electromagnetic Method
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