Study On Suppressing The Static Effect Of Three-dimensional Magnetotelluric Sounding Data Based On Wavelet Packet

Magnetotelluric (MT) Sounding, with the advantages of convenient wild construction, the lower cost, the deeper depth of invertigation, and being free from the shielding of resistive formation, is widely used to energy exploration. The existence of static effects in the frequency domain electromagnetic sounding makes the Magnetotelluric sounding data interpretation complicated and causes errors in the depth of speculation. Based on the study of domestic and international various correction method of static effects,this paper, studied the wavelet theory to process the static effects of three-dimensional Magnetotelluric Sounding data using two dimension under the help of 863 project(2007AA06Z134).First the paper discussed background of the research and current situation, explained the research on the suppression method of static effect, and state wavelet transform and wavelet neural network development and origins. The good frequency analysis characteristics of the wavelet transform provides a very effective tool for noise cancelling and constructing filter. The main work is as follows:Firstly, it describes the physical cause and the characteristic of Magnetotelluric sounding data static effects, discusses the difference between two-dimensional and three-dimensional static effects, gives the methods of suppressing the static effect of three-dimensional MT sounding.Secondly, the paper from the basic principle of wavelets transform, in view of the denoising principle of wavelet analysis, researches the application of two-dimensional wavelet in the suppression static effects of three-dimensional Magnetotelluric data. It makes use of the two-dimensional wavelet transform decomposition and reconstruction algorithms, its good frequency analysis characteristics, to introduce the denoising factor to choose threshold function and the threshold criteria reasonably, and then by simulating the three-dimensional earth electricity model and the measured data that have static effect, shows that the two-dimensional wavelet transform analysis can separate the static effect from three-dimensional magnetotelluric sounding data. Then, using the two-dimensional wavelet analysis to reconstruction algorithm can get the Cagniard apparent resistivity which is suppressed the static effect. Experiments show that the method can reflect the layered characteristics of the original model easily according to the principle of eliminating static effect, and the static effect produced by the small three-dimensional subject can be well suppressed.In addition, the paper studies on the wavelets packet. The wavelet packet transform's frequency characteristics is better than wavelet transform's. It can analyse the high-frequency parts of signal which was not processed by the wavelet transform, showing the better detail analysis ability. Based on the fine features of wavlet packet, we proposed the methods to suppress the static effect that the two-dimensional wavelet packet analysis in the three-dimensional MagnetoTelluric data. Using this method to oppress the static effect of three-dimensional magnetotelluric sounding data, firstly, we apply the minimum entropy criteria to choose the best wavelet packet basis function, processing the cagniard apparent resistivity curse, and then separate out the high-frequency part, which is called static effect. Then reconstruct it and get the apparent resistivity. Because wavelet packet detailed analysis shows a better ability, when needed, use this feature to extract the two-dimensional and three-dimensional magnetotelluric sounding data suppression of the static effects, and reconstruct the heterogeneous body details that causes the static effects.The above study shows that two-dimensional wavelet analysis and two-dimensional wavelet packet have the good characteristics of part analysis, by a reasonable choice of wavelets (packet) and the the number of decomposition layers, using the two methods to static effects cancelling, it have a good result to process the static effect of magnetotelluric sounding data by means of the two-dimensional wavelet analysis.Finally, the thesis discusses the algorithm deficiencies of the system that static effect suppressing of three-dimensional magnetotelluric sounding data, and proposes some suggestions about the further research work.