Research On Seismic Surface Wave Suppression Based On Fractional Fourier Transform

Seismic exploration is an artificial method and it uses explosives or dynamite source excitating wave, and researchs seismic wave propagation in the formation of the law to identify methods of underground geological structures based on rock elastic. In the land reflection seismic exploration, surface wave spreading along the ground is a regular interference wave and it's energy is strong.usually in the seismic records,surface wave shows the dispersion characteristics, and has low apparent velocity; what's more ,because of the linear distribution taked on the gathering , strong energy, low frequency and vibration continued for a long time, surface wave has an serious effect on the deep impact of the effective reflection. If surface wave is not effectively suppressed, we can not obtain a more objective gathering signals spherical proliferation and attenuation compensation function, so it is bound to affect the treatment effect of time-frequency domain amplitude compensationt and lower noise-signal ratio of seismic data. To obtain high noise-signal ratio of seismic records, surface wave suppression is an important part.Currently, methods of High-pass filtering, K-L transform and F-K filtering are commonly used to suppress surface wave.although these methods can effectively separate surface wave from the data, it undermines the effective wave. In recent years, with the maturation and development of fractional fourier transform theory, fractional fourier transform theory has been widely used making its signal processing. However, in the field of seismic signal processing applications has not yet made the appropriate research. in order to find better ways to suppress surface wave, This paper aims to explore the use of fractional fourier transform processing of surface wave. In summary, in recent years ,with the gradual rise research on the theory of the basic method of fractional fourier transform, fast algorithm and application in signal processing advantages, combined with the seismic characteristics and features of the formation of surface wave analysis, surface wave suppression based on the fractional fourier transform was proposed. Main contents and findings are as follows:The basic concepts and typical nature of the fractional fourier transform was proposed from the time-frequency analysis. Several commonly fast algorithm for the theory are put forward to do theory bedding for the later application. Combining with the advantages of fractional fourier transform, the fractional fourier transform have made extensive use in signal processing and provides the better basis for surface wave suppression.The surface wave of the classification, causes, transmission and characteristics are further studied,and the surface wave features on seismic records are also analyzed. The fractional fourier transform filtering and interference principle of the separation are proposed.To achieve the purpose of removing interference, the optimal filter is designed based on the fractional domain minimum mean square error.This paper mainly introduces that how to suppress surface wave based on the fractional fourier transform. Combining with the characteristics of surface wave and the principle of fractional fourier transform filter, this paper proposes integral method and segmentation method to deal with the actual seismic data.1) The integral method: To suppress surface wave,all the seismic data is transformed by using the same transformation parameter and surface wave components are removed by the same fractional domain filter.2) The segmentation method: according to analyzing the surface wave characteristics and observing its position in the seismic images show , the data is split into four parts, then each part that characterizes the image features can be deal with the data processing. through the channel number of each part of the typical data processing, the best parts of the corresponding transformation parameters and design filter can be found out, then all parts of the filtered signals are reversed rotation back to the time domain to observe the treatment of the seismic data. Actual processing results show that the segmentation method is better than the integral method. Finally, the two-dimensional wavelet transform method is also used to process seismic data and the processed results are compared with the results of fractional fourier transform method. though the comparation, the feasibility of the fractional fourier transform to suppress of surface wave is verified and strengths and weaknesses of three processing methods are found out;in order to achieve better results, the next step of the improved algorithm is proposed.This paper completes further research of Seismic surface wave characteristics and laws , achieves the optimal filter algorithm analysis based on minimum mean square error and its simulation application ,and completes the results treatment analysis of the two-dimensional wavelet transformation based on seismic surface wave.What's more , Improvement of the methods are put forward. The most important thing is the achievement that the fractional fourier transform is used to suppress surface waves, and this achievement expands its applications field in seismic signal processing, and provides important preparatory work for more exploration to use the fractional fourier transform processing seismic surface waves in the future. At the same time , it's also mining the application potential of the fourier transform in signal processing .