Xiaokai Wang

A New Tiling Scheme for 2-D Continuous Wavelet Transform With Different Rotation Parameters at Different Scales Resulting in a Tighter Frame

A desirable property when dealing with frames is that the low and up bounds of frames should be close to each other. This can accelerate the convergence speed in computing the dual-frame and simplify the process of recovering the signal from its frame coefficients. In this letter, a new 2-D continuous wavelet transform tiling scheme, which uses different rotation factor sampling methods for different scales, is proposed. The upper/lower bound of the 2-D wavelet family based on this new tiling scheme is derived. The upper/lower bound of the 2-D Morlet wavelet family is estimated, and the results show that the 2-D wavelet family based on the new tiling scheme can provide a higher lower bound and a lower upper bound compared with the 2-D wavelet family based on the old tiling scheme.

Qualitative seismic attenuation parameter estimation based on prestack data in the continuous wavelet domain

AbstractBecause the seismic wave propagates through the subsurface, part of the elastic energy eventually ends up as heat energy. This phenomenon is known as absorption (or anelastic attenuation). The factors causing anelastic attenuation include fluid movement and grain boundary friction. The seismic quality factor (Q) quantifies the anelastic attenuation and is commonly used in assisting reservoir characterization. However, current Q-estimation approaches are mainly implemented on a poststack seismic volume. The Q-estimation approaches applied to poststack seismic data assume that the seismic data are normal incident reflections, and they do not consider the effect of the travel path on seismic attenuation. In theory, the attenuation degree of the low-frequency component should differ from the attenuation degree of the high-frequency component for large-offset seismic data. We have developed a method to qualitatively estimate seismic attenuation in the prestack seismic domain. A continuous wavelet trans...

Hybrid image denoising method based on non-subsampled contourlet transform and bandelet transform.

The second generation bandelet transform uses the two-dimensional (2D) separable wavelet transform to improve its image denoising and compression performance. However, the 2D separable wavelet transform is not a shift-invariant transform and therefore cannot capture geometric information well. The authors propose a hybrid image denoising method in which the 2D separable wavelet transform in the second generation bandelet transform is replaced with the non-subsampled contourlet transform. The results of the application of the proposed method to several greyscale and colour benchmark images contaminated with various levels of Gaussian white noise and Poisson noise indicate that the proposed method has good peak signal-to-noise ratio and visual quality performance.

A Fast 3rd Generation Coherence Algorithm Realizing Method

Summary The 3rd generation coherence algorithm, which was proved to be an excellent tool to detect faults and has good antinoise ability, was restricted by its large computational cost on constructing covariance matrix and eigen decomposition. We aim at this problem in this paper and propose an efficient realizing method which was based on recursion and power algorithm to accelerate the 3rd generation algorithm. The results on field data show that our method can greatly reduce calculation.

Comparison of the DG finite element method with finite difference method for elastic-elastic interface

In some seismic numerical applications we have to simulate wave propagation with sharp medium discontinuities. The rotated staggered grid (RSG) finite difference (FD) scheme and the arbitrary high-order derivatives discontinuous Galerkin (ADER-DG) finite element (FE) scheme can both be used for the problem of strong material heterogeneities. In this paper we study their behavior in a two-layer model with a varying ratio of the material parameters in the first layer to the second. We compared the results of the numerical schemes with the exact solution. The FD method and the FE method can both get small envelop misfits. The FE scheme has advantage over the FD method on phase misfits, but it needs a high CPU effort.

On the method of detecting the discontinuity of seismic data via 3D wavelet transform

We propose a seismic discontinuities detecting method based on wavelet transform in this paper. First we do 1DCWT to seismic cube to obtain instantaneous phase cubes for three interested scale. Then we use 3D CWT as a novel tool to detect seismic discontinuities on these three instantaneous phase cubes. The result on synthetic signal and real field data show our methods depicting ability of large fault and tiny discontinuities.

Seismic quality factor estimation using continuous wavelet transform

In this paper, seismic quality factor Q estimation from vertical seismic profile (VSP) data is discussed, by using continuous wavelet transform (CWT). We suppose that source signature is a general constant-phase wavelet which matches the real one better. Based on the CWT of a reference and a target recording, we derive the formula of frequency-independent Q estimation by the ratio of wavelet-domain peak amplitude of these two recordings. Wavelet-domain peak amplitude denotes the peak module of CWT of the recording with every fixed scale. The formula is related to the dominant frequency and standard deviation of source signature. And the Q estimation formula with impulse source can be considered as its specific case that the standard deviation of source approaches the infinity. The synthetic zero-offset VSP and real field tests demonstrate that in the condition of constant-phase source signature, estimated Q from our formula can provide more accurate information than that by the formula with impulse source.

2D Seismic Attributes Extraction Based On Two-dimensional Continuous Wavelet Transform

Summary Seismic attributes play an important role in interpretation and reservoir characterization. We use two dimensional wavelet transform (2D CWT) as a tool to extract 2D seismic attributes. Large scale 2D CWT can be used to estimate local dip, while small scale 2D CWT can be used to detect local discontinuity and its direction. Using the local discontinuity extracted by 2D CWT and directional filtering, we get a method to detect faults in 2D data. We use 2D CWT on synthesis data and oilfield data, and the results show that 2D CWT can extract 2D seismic attributes efficiently.