paul sava


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© 2007 PC Sava

Page updated on
April 7, 2018

Angle-domain common image gathers


Migration by wavefield extrapolation produces common-image gathers in the offset domain, where most of the energy is focused around zero offset. In this context, offset represents an image parameter, and it is different from the offset at the surface, which is a data parameter. Common-image gathers from migrated images can be transformed to the angle domain, where we observe reflectivity function of scattering/reflection angle. Angle gathers can be computed before imaging or after imaging. I compute angle-domain CIGs after imaging for computational and convenience reasons. Applications for angle gathers are migration velocity analysis (MVA) and amplitude vs. angle (AVA) analysis.


The pictures below depict a migrated image of a well-known synthetic model and two common-image gathers at a location indicated by the vertical line on the image. One frame corresponds to an offset-domain CIG, and the other frame corresponds to an angle-domain CIG. The various events in angle-domain CIGs are flat, indicating a correct velocity model and correct migration. The angle-domain CIGs show variations of angular coverage with depth and gaps, which indicate limited and variable illumination at various points in the image.

References

Rickett, J., Sava, P.C., 2002, Offset and angle-domain common image-point gathers for shot-profile migration, Geophysics, v. 67, no. 3, pp. 883-889. (PDF)
Sava, P.C., Fomel, S., 2003, Angle-domain common-image gathers by wavefield continuation methods, Geophysics, v. 68, no. 3, pp. 1065-1074 (PDF)

Figures can be used freely for non-profit educational purposes by acknowledging their source:
© Paul Sava, Center for Wave Phenomena, Colorado School of Mines
http://www.mines.edu/~psava