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2D Forward Of Time-domain Of ELF Electromagnetic

Posted on:2015-01-10Degree:MasterType:Thesis
Country:ChinaCandidate:Z H XuFull Text:PDF
GTID:2250330428966893Subject:Geological Engineering
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Consider the impact of ionospheric ELF electromagnetic method is anemerging, with a very broad prospect and research value using a geophysicalelectromagnetic detection methods.This approach overcomes the smaller coverage ofcontrolled source audio magnetotelluric,probing deep enough;Magnetotelluric of thesignal is weak,vulnerable to interference.Extremely Low Frequency electromagneticmethod being geophysicist attention because of its strong signal, wide coverage,probing depth caused. Extremely low frequency electromagnetic method in the nearfield, far field communication theory and controlled source audio magnetotelluricsimilar, they rely mainly on conducting current spread, then the effects of air currentsand displacement caused by the ionosphere can be ignored and electromagneticinduction field is mainly; In the waveguide region rely mainly spread displacementcurrent, conduction current can be ignored, but must consider the impact of theionosphere. Therefore, the study considered the impact of ionospheric ELFelectromagnetic modeling and inversion technique is of great important.In this paper, considering the IP effects and ionospheric of ELFelectromagnetic2-D forward. Use of secondary field algorithm, based on Maxwell’sequations were derived two coupled partial differential equations; Using the finiteelement method, put the study area four-node isoparametric element mesh, to achievea continuous function discrete, will solve the coupled partial differential equationsinto solving the matrix equation. Using the Cole-Cole model to characterize thecomplex resistivity values into a matrix equation.Using Compressed Row Storage tostore the overall coefficient matrix. Deduced primary field computational formula thatconsidering the ionospheric effects of extremely low frequency electromagneticwave-number domain based on Maxwell’s equations. And by comparison with thenumerical solution of1-D CSEM verify the correctness of the derivation formula. Usethe Symmetrical gradually Over Relaxation Preconditioned Conjugate Gradientmethod to solve the matrix equation. Get the y-direction wave-number domain of thesecondary field electromagnetic field values. According to its relationship with other components of the electromagnetic field, and seek other directions secondaryelectromagnetic field value in the wave-number domain. The frequency-wavenumberdomain inverse fourier transform to the frequency-space domain, continue inversetransform to the time domain. To achieve the2-D forward modeling of the ELFelectromagnetic method in consideration of ionospheric effect.We establishment the layered model. And used the results of one-dimensionalnumerical solution and two-dimensional numerical solutions comparison. And verifythe correctness of the forward algorithm. Simulate several geoelectric model. Throughforward calculation and analysis of the x-direction of the electric field total field intime domain response characteristics. Through the complex resistivity anomaliesimpedance models give different values for each parameter to observe and analyze thechanges in the parameters of the z-direction of the magnetic field of thesecondaryeffects of time domain response curve case.
Keywords/Search Tags:Extremely Low Frequency, Cole-Cole model, Finite element method, 2Dforward, Ionosphere effect
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