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The2.5D Forward Modeling Of Controlled Source Audio Frequency Magnetic

Posted on:2013-05-01Degree:MasterType:Thesis
Country:ChinaCandidate:W J FengFull Text:PDF
GTID:2230330374488722Subject:Earth Exploration and Information Technology
Abstract/Summary:PDF Full Text Request
Controlled Source Audio-Frequency Magnetic Sounding Method (CSAFMAG) aims to solve the static shift of frequency sounding methods basing on the Cagniard resistivity and the limitations of natural source of AFMAG. CSAFMAG, using the harmonic electromagnetic fields excited by artificial source, only measuring the magnetic field, has controlled source and little effect of the static shift. Obviously, for any geophysical methods, forward modeling is the extremely foundations for method researching, apparatus designing, data processing and interpretation and so on. Considering a three dimensional source and two dimensional geological structure, studying the two and half dimensional forward modeling of CSAFMAG and fast modeling the response of complex geoelectric structure establish the base for the development and application of this novel method.In this paper, firstly, for representing the response of CSAFMAG to subsurface geoelectric structure, this paper introduces the frequency tipper. By Hankel Transformation, this paper calculates the homogeneous stratiform CSAFMAG. The results demonstrate that, in far zone, the response of frequency tipper corresponds to the parameters of subterranean geoelectric structures, attesting the reliability of frequency tipper. Then, this dissertation utilizes rectangle mesh and bilinear interpolation of the finite element method acquiring the2.5dimensional modeling of CSAFMAG. In order to conveniently, stably and fast solve the large sparse equations, this paper uses Dirichlet boundary condition, adopts incomplete LU decomposition preconditioning the ensemble coefficient matrix and uses bi-conjugate gradient stabilized method solves the equations. Furthermore, to ensure the accuracy and reduce time, this paper employs15particular wavenumbers of Fourier Transformation, achieving the two dimensional modeling of three dimensional source. In addition, employing pseudo-delta reduces the singularity of nearby zoon of artificial source. What’s more, using Matlab compiles the program of2.5dimensional CSAFMAG modeling and presents the response of several special geoelectric models, showing that in far zone, the variation of frequency tipper corresponds to the change of resistivity of underground targets and verifying the validity and reliability of the program. At last, for eliminating the effect of space between receiver and transmitter to frequency tipper, using the frequency tipper’s value of highest frequency normalizes the frequency tipper’s value at the same station.Basing on these researches, this paper acquires that frequency tipper could reflect the resistivity variation of geoelectric structures; simplifying the three dimensional source into two dimensional can satisfy the numerical modeling of CSAFMAG with artificial source; the particular wavenumbers of Fourier Transformation can enhance the stability and speed of the numerical modeling; using the normalization by frequency tipper’s value of highest frequency could eliminate the effects of space between receiver and transmitter.
Keywords/Search Tags:CSAFMAG, frequency tipper, 2.5dimensional forwardmodeling, finite element method
PDF Full Text Request
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