Wang Chengxiang

Prestack coherent noise suppression in the 2D wavelet domain

Summary The elimination of linear and nonlinear noises such as the multiple refractions and the surface waves in the pre-stack data is generally done separately, which decreases the fidelity of the signal and the data processing efficiency. Because the wavelet function is localized in the time and frequency domain, we used a least-square adaptive subtraction method (LMS) to attenuate linear and nonlinear noises simultaneously in the 2D wavelet domain. In the LMS method, we first used part of the 2D wavelet coefficients to predict the noise model, and then subtracted it from the wavelet coefficients of the data to get the coefficients corresponding to the signal. Finally the signal is estimated by reconstructing the subtracted wavelet coefficients. We tested this method to both synthetic and real data and successfully removed those linear and nonlinear noises.

A prestack depth migration method with large extrapolation step size and its application

Summary One of the most important issues with the wave equation prestack depth migration (PSDM) is how to reduce the computational cost. At present there are mainly two means, besides an extrapolation algorithm. One is to reduce the volume of the prestack data, for example, various synthetic methods. The other is to reduce the total number of extrapolation steps by using a large extrapolation step size. Here we present a new PSDM method using a large extrapolation step size which combines the methods mentioned above. In our method, the plane wave synthetic method is used to reduce the prestack data, and the large step size is used for wavefield extrapolation to further reduce the computation cost of the PSDM method. At the same time, a phase-shifted linear interpolation method is used to interpolate the extrapolated wavefield which can significantly improve the accuracy of the migration results. The results of the 2-D Marmousi and Salt model show that the method improves the computational efficiency several times over and at the same time maintains the same image quality compared with the conventional method.