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Conclusions

We conclude that operator aliasing artifacts are indeed introduced during prestack wavefield continuation migration when s- or r-axes are allowed to deviate from a regular grid. This problem is thus manifest both when we choose to subsample the number of shots available from the data or design a survey without shots at every receiver location (or in reciprocal cases like OBC surveys). We have shown two methods for eliminating aliased contributions to the image.

We feel that it is more appropriate to use selective energy imaging conditions rather than a fat source function. In practice, lateral velocity variation will cause energy constituents in the fk-plane to move around. To allow for any beneficence from this movement, it would be unwise to propagate a band-limited source function, or worse, to eliminate energy from the source and receiver wavefields during propagation steps. Therefore we recommend migrating individual shots on the fine grid, and accounting for image aliasing in the imaging step rather than propagating data decimated to match the grid of the subsampled shot axis (or vice-versa).

With some knowledge of the dip content of the data it is possible to extend the boundaries of anti-aliasing limit criteria. Using both positive and negative one-sided band-limits can allow for the inclusion of appropriate energy into the image that resides outside of the rigorously defined Nyquist boundaries. Therefore, when challenged with imaging important steeply dipping targets, decisions concerning acquisition design or the level of decimation along different directions for migration can be made with a better understanding of the consequences to the final product.


next up previous print clean
Next: REFERENCES Up: Artman et al.: Aliasing Previous: Experiment
Stanford Exploration Project
7/8/2003