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Coherent noise attenuation for passive seismic data based on iterative two dimensional model shrinkage

100%

Hu B. , Jia Z. , Zhang L.

tom Vol. 69, no. 3

773--782

Passive seismic source imaging can be utilized to recover geophysical information from subsurface ambient noise. Compared with conventional active seismic exploration, passive seismic source imaging is cost-efective and environmentally friendly. However, passive data acquisition cannot easily satisfy the theoretical condition, leading to noised virtual-shot gathers. Furthermore, coherent noise limits the application of passive source data. Although image quality improvement techniques for passive source data have recently attracted considerable interest, the denoising problem for virtual-shot gathers is seldom considered. In this study, we propose an iterative denoising approach for passive seismic data. The criterion used to extract useful signals is the diference between the wavefeld similarity of useful events and the coherent noise in various gathers, i.e., the common shot gather and common receiver gather. We adopted local similarity to measure the similarity level and extract major useful events. However, the close local similarity between weak events and coherent noise may cause signal leakages and singular noise residuals. We incorporated an iterative two-dimensional model shrinkage algorithm into the denoising process to suppress the singular noise residual and highlight useful events. The proposed approach can overcome the limits of strong coherent noise in virtual-shot gathers, which can extend the choice range for data processing. Synthetic and feld examples demonstrate a promising coherent noise attenuation performance, illustrating the efectiveness and feasibility of the proposed method. The denoised migrated section exhibits a smaller depth error and higher quality

An efficient low-frequency artifact suppression method at excitation time for excitation amplitude imaging condition

75%

Wang R. , Wang D. , Hu B. , Zhang W. , Zhou J. , Li B.

tom Vol. 71, no. 3

1225--1240

The excitation amplitude imaging condition (EAIC) is a high-resolution, computationally efficient, and low-storage imaging condition in reverse time migration (RTM). However, when there are strong reflection interfaces in the velocity model, they will produce low-frequency artifacts, which seriously contaminate the RTM image. The artifacts can be removed by the wavefield decomposition algorithm, but this process always performed by analytic time wavefield extrapolation, which needs extra wavefield extrapolation. Furthermore, an extra source wavefield extrapolation is required to determine the excitation time before the migration. Thus, the additional wavefield extrapolations can seriously damage the computationally efficient advantage of the EAIC. By taking advantage of the directivity and low storage of excitation amplitude, we present a low-frequency artifact suppression method with no extra wavefield extrapolation. Poynting vector, reference traveltime and minimum amplitude threshold are combined to constraint the excitation amplitude updating process, and it makes the excitation amplitude more consistent with the definition of excitation criterion. We can directly obtain a noise-free excitation amplitude without the source wavefield decomposition. Instead of the analytic time wavefield extrapolation, the time-bin technique and the windowed Hilbert transform are combined to achieve the receiver wavefield decomposition only at the excitation time. The numerical results show that our method can effectively suppress the low-frequency artifacts in the image with no extra wavefield extrapolation.