scholarly journals Efficient dip-angle angle-domain common-image gather estimation using Poynting vector in acoustic reverse time migration and its application in noise suppression

2018 ◽  
Vol 66 (9) ◽  
pp. 1714-1725 ◽  
Author(s):  
Qiancheng Liu ◽  
Jianfeng Zhang
Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. S159-S169 ◽  
Author(s):  
Qiancheng Liu

Angle-domain common-imaging gathers (ADCIGs) are important in analyzing the subsurface discontinuities where reflection waves take place. In elastic reverse time migration (ERTM), dip-angle ADCIGs can be computed postmigration via subsurface offset extension. We have obtained dip-angle ADCIG premigration in ERTM by using the Poynting vector, which was easy to compute during wavefield propagation. The reflection normal of PP imaging is the bisector of the scattering angle, whereas that of PS imaging is not. We derive formulas for PP and PS dip-angle estimations, respectively, with some straightforward vector operations. Similar to the subsurface-offset one, our method also outputs dip-angle ADCIGs with the appearance of blocky horizontal coherence. According to local semblance analysis, the signal with a better horizontal coherence promises a higher semblance score, and vice versa. We can thus design a specular filter to suppress incoherent noises according to their corresponding local semblance scores. We validate our methods with numerical examples. The Graben and Marmousi data sets show that our methods work effectively in dip-angle ADCIG computation and the following noise suppression in ERTM. We also examine our methods with one field data set.


2013 ◽  
Author(s):  
Edvaldo S. Araujo ◽  
Reynam C. Pestana ◽  
Adriano W. G. dos Santos

Geophysics ◽  
2012 ◽  
Vol 77 (5) ◽  
pp. S105-S115 ◽  
Author(s):  
Rui Yan ◽  
Xiao-Bi Xie

An angle-domain imaging condition is recommended for multicomponent elastic reverse time migration. The local slant stack method is used to separate source and receiver waves into P- and S-waves and simultaneously decompose them into local plane waves along different propagation directions. We calculated the angle-domain partial images by crosscorrelating every possible combination of the incident and scattered plane P- and S-waves and then organized them into P-P and P-S local image matrices. Local image matrix preserves all the angle information related to the seismic events. Thus, by working in the image matrix, it is convenient to perform different angle-domain operations (e.g., filtering artifacts, correcting polarity, or conducting illumination and acquisition aperture compensations). Because local image matrix is localized in space, these operations can be designed to be highly flexible, e.g., target-oriented, dip-angle-dependent or reflection-angle-dependent. After performing angle-domain operations, we can stack the partial images in the local image matrix to generate the depth image, or partially sum them up to produce different angle-domain common image gathers, which can be used for amplitude versus angle and migration velocity analysis. We tested several numerical examples to demonstrate the applications of this angle-domain image condition.


Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. S359-S376 ◽  
Author(s):  
Chen Tang ◽  
George A. McMechan

Because receiver wavefields reconstructed from observed data are not as stable as synthetic source wavefields, the source-propagation vector and the reflector normal have often been used to calculate angle-domain common-image gathers (ADCIGs) from reverse time migration. However, the existing data flows have three main limitations: (1) Calculating the propagation direction only at the wavefields with maximum amplitudes ignores multiarrivals; using the crosscorrelation imaging condition at each time step can include the multiarrivals but will result in backscattering artifacts. (2) Neither amplitude picking nor Poynting-vector calculations are accurate for overlapping wavefields. (3) Calculating the reflector normal in space is not accurate for a structurally complicated reflection image, and calculating it in the wavenumber ([Formula: see text]) domain may give Fourier truncation artifacts. We address these three limitations in an improved data flow with two steps: During imaging, we use a multidirectional Poynting vector (MPV) to calculate the propagation vectors of the source wavefield at each time step and output intermediate source-angle-domain CIGs (SACIGs). After imaging, we use an antitruncation-artifact Fourier transform (ATFT) to convert SACIGs to ADCIGs in the [Formula: see text]-domain. To achieve the new flow, another three innovative aspects are included. In the first step, we develop an angle-tapering scheme to remove the Fourier truncation artifacts during the wave decomposition (of MPV) while preserving the amplitudes, and we use a wavefield decomposition plus angle-filter imaging condition to remove the backscattering artifacts in the SACIGs. In the second step, we compare two algorithms to remove the Fourier truncation artifacts that are caused by the plane-wave assumption. One uses an antileakage FT (ALFT) in local windows; the other uses an antitruncation-artifact FT, which relaxes the plane-wave assumption and thus can be done for the global space. The second algorithm is preferred. Numerical tests indicate that this new flow (source-side MPV plus ATFT) gives high-quality ADCIGs.


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