Conclusions

We construct offset-domain common-image gathers after shot-profile migration. The offset-domain gathers then can be transformed to the angle domain by Sava and Fomel's 2000 transformation where residual moveout can be used for velocity analysis or image enhancement. The angle domain also potentially contains information about reflectivity as a function of angle that can be used to infer rock properties across the reflecting interface.

For sparse-shot geometries, suitable for shot-profile migration, however, the problem of shot-aliasing remains. Shot aliasing can cause corruption of the angle domain gather, rendering simple moveout-based velocity analysis very difficult.

 

offcov4000
Figure 5 Poorly illuminated offset-domain common-image gathers. Panels (a), (b), and (c) were migrated with velocity models that were correct, 6% too low, and 6% too high, respectively. Shot spacing was 500 m, instead of 25 m for Figure 3.

 

angcov4000
Figure 6 Poorly illuminated angle-domain common-image gathers. Panels (a), (b) and (c) were migrated with velocity models that were correct, 6% too low, and 6% too high, respectively. Shot spacing was 500 m, instead of 25 m for Figure 4.