An Iterative Focal Denoising Strategy for Passive Seismic Data
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Pure and Applied Geophysics
An Iterative Focal Denoising Strategy for Passive Seismic Data BIN HU,1
DELI WANG,1 and RUI WANG1
Abstract—Passive seismic source imaging can extract geophysical information from underground noise and has been widely utilized in geophysical research. Compared with conventional active seismic exploration, it is low-cost and eco-friendly; however, the application of passive seismic data is limited by coherent noise in the virtual-shot gathers. An approach involving direct denoising in the virtual-shot gathers has not previously been discussed; therefore, we present an iterative denoising strategy for passive seismic data. The reflection-preserving characteristic of focal transformation is adopted in the virtual-shot gathers to eliminate the coherent noise, and L1-norm sparse inversion is utilized to obtain a more accurate solution during focal transformation. A key aspect of this strategy is clean focal operator building at high noise levels. We apply local similarity as the criterion for extracting the majority of reflection energy for the focal operator. Because of strong coherent noise, a clean focal operator cannot be obtained in one iteration. We therefore obtain both denoised passive seismic data and a clean focal operator by denoising using a cleaner focal operator and operator building using updated denoising results. The presented approach can overcome the limits of coherent noise in virtual-shot gathers, which is significant for subsequent data processing and wider application. Synthetic examples achieve excellent performance in coherent noise attenuation and reflection energy reconstruction, especially in far-offset sections. Keyword: Passive seismic data, denoising, local similarity, focal transformation, sparse constraint.
1. Introduction Passive seismic source imaging can extract geophysical information by interferometry (Claerbout 1968). Its idea is retrieving reflection response from underground noise based on the stationary phase method (Schuster et al. 2004). This noise comes from many sources and displays excitation of different
1 College of Geo-Exploration Science and Technology, Jilin University, Changchun 130026, People’s Republic of China. E-mail: [email protected]
periods and wavelets, and the entire range can be received by every receiver on the Earth’s surface (Calvert et al. 2004). Virtual-shot gathers can then be obtained by cross-correlation and have the same observation system as active seismic data, which indicate geophysical information. Compared with conventional active seismic exploration, passive seismic source imaging is environmentally friendly and costefficient (Wapenaar et al. 2010a, b; Zhu et al. 2012), yet coherent noise in the virtual-shot gathers limits the applications of passive seismic data. To improve the signal-to-noise ratios (SNR) of virtual-shot gathers, deconvolution and multidimensional deconvolution is often proposed (Wapenaar et al. 2011). However, an approach involving direct denoising in the virtual-shot gathers has not y
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