
Combining Multidirectional Source Vector with AntitruncationArtifact Fourier Transform to Calculate Angle Gathers from Reverse Time Migration in Two Steps 
Author(s): 
Tang, Chen; McMechan, George A. 

20170811 

article 
Keywords:  Show Keywords 

Because receiver wavefields reconstructed from observed data are not as stable as synthetic source wavefields, the sourcepropagation vector and the reflector normal have often been used to calculate angledomain commonimage 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 Poyntingvector 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 (k) 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 sourceangledomain CIGs (SACIGs). After imaging, we use an antitruncationartifact Fourier transform (ATFT) to convert SACIGs to ADCIGs in the kdomain. To achieve the new flow, another three innovative aspects are included. In the first step, we develop an angletapering scheme to remove the Fourier truncation artifacts during the wave decomposition (ofMPV) while preserving the amplitudes, and we use a wavefield decomposition plus anglefilter 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 planewave assumption. One uses an antileakage FT (ALFT) in local windows; the other uses an antitruncationartifact FT, which relaxes the planewave assumption and thus can be done for the global space. The second algorithm is preferred. Numerical tests indicate that this new flow (sourceside MPV plus ATFT) gives highquality ADCIGs. 

Society of Exploration Geophysicists 

00168033 

Geophysics 

http://dx.doi.org/10.1190/GEO20160408.1 

http://hdl.handle.net/10735.1/6079 

Tang, C., and G. A. McMechan. 2017. "Combining multidirectional source vector with antitruncationartifact Fourier transform to calculate angle gathers from reverse time migration in two steps." Geophysics 82(5), doi:10.1190/GEO20160408.1 

©2017 Society of Exploration Geophysicists 
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