Wave-equation migration with dithered plane waves

Wave-equation based shot-record migration provides accurate images but is computationally expensive because every shot must be migrated separately. Shot-encoding migration, such as random shot-encoding or plane-wave migration, aims to reduce the computational cost of the imaging process by combining the original data into synthesized common-source gathers. Random shot-encoding migration and planewave migration have different and complementary features: the first recovers the full spatial bandwidth of the image but introduces strong artefacts, which are due to the interference between the different shot wavefields; the second provides an image with limited spatial detail but is free of crosstalk noise. We design a hybrid scheme that combines linear and random shot-encoding in order to limit the drawbacks and merge the advantages of these two techniques. We advocate mixed shot-encoding migration through dithering of plane waves. This approach reduces the crosstalk noise relative to random shot-encoding migration and increases the spatial bandwidth relative to conventional plane-wave migration when the take-off angle is limited to reduce the duration of the plane-wave gather. In turn, this decreases the migration cost. Migration with dithered plane waves operates as a hybrid encoding scheme in-between the end members represented by plane-wave migration and random shot-encoding. Migration with dithered plane waves has several advantages: every synthesized common-source gather images in a larger aperture, the crosstalk noise is limited and higher spatial resolution is achievable compared to shot-record migration, random shot-encoding and linear shot-encoding, respectively. Computational cost is also reduced relative to both random and linear shot-encoding migration since fewer synthesized commonsource gathers are necessary to obtain a high signal-to-noise ratio and high spatial resolution in the final image.