Offset and angle‐domain common image‐point gathers for shot‐profile migration

Abstract

Prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially cost‐effective for sparse‐shot wide‐azimuth geometries. The interpretation of offset as the displacement between the downward‐propagating (shot) wavefield and upward‐propagating (receiver) wavefield enables us to extract offset‐domain common image‐point (CIP) gathers during shot‐profile migration. The offset‐domain gathers can then be transformed to the angle domain with a radial‐trace mapping originally introduced for shot‐geophone migration. The computational implications of this procedure include both the additional cost of multioffset imaging and an implicit transformation from shot‐geophone to midpoint‐offset coordinates. Although this algorithm provides a mechanism for imaging angle‐dependent reflectivity via shot‐profile migration, for sparse‐shot geometries the fundamental problem of shot‐aliasing may severely impact the quality of CIP gathers.