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Next: Shot-Profile Migration Up: Artman et al.: Aliasing Previous: Axes and allies

Flat earth synthetic

A synthetic data set was generated to test the first two methods of preventing aliasing. Shot-gathers were modeled over a 2000m/s earth model with one flat reflector at 1000m. Nominal shot, $\Delta s$, and receiver, $\Delta r$, spacing is 10m. Dominant frequency of the wavelet is 30Hz. Migration experiments were performed using both shot-profile and source-receiver algorithms. The analysis and conclusions are valid for both shot-geophone and shot-profile migrations due to their mathematical equivalence Biondi (2003); Shan and Zhang (2003). However, in practice there are subtle differences between the two that will be discussed later.

The data so generated has been imaged with a split-step Fourier wave equation continuation migration kernel. The same continuation operator has been implemented in both shot-profile and source-receiver formulations. The complex valued image at the depth of the reflector was extracted without the normal summation of the frequency axis to aid in interpretation. Fourier transforms of the surface location and subsurface offset axes were then applied. Both migration strategies were used to examine several cases of data completeness. For the shot-profile migration example, four cases were considered: 1) shots at every receiver location, 2) shots at every tenth receiver location, 3) shots at every tenth receiver location imaged with a band-limited source function, and 4) shots at every tenth receiver location imaged with the selective energy imaging condition. For the source-receiver example, three cases were considered: 1) migration of all CMP's, 2) migration of CMP's from shot placements every tenth receiver location, and 3) migration of subsampled data appropriately filled with zero-traces to regain the size of the original data set. Despite the large decimation of the data for these experiments, care was taken to assure that the data were still appropriately sampled after decimation to assure that the conclusions drawn from these results are not due to acquisition aliasing.