Examples

The same synthetic model (Figure ) that we used in the previous section is used here. The wavefield recorded on the irregular topography in Figure (b) clearly demonstrates the effect of the filter. The wavefield traveling vertically does not differ from the result of the first scheme, but the wavefield traveling with some stepout shows differences. In Figure (b), the right limb of the bow-tie shows more pronounced amplitude change which depends on the slope of the surface topography. Locations with the same slope as the stepout of the wavefield does not differ from the result of the first scheme (Figure (b)) but the amplitude has been significantly reduced at the locations with the opposite slope of the stepout of the wavefield.

From the result of the migration in Figure (d), we can see the noise is suppressed significantly. Comparing to Figure (d), the datumed result in the Figure (c) has also improved. The datumed wavefield in Figure (c) still displays the effect of the irregular topography. There is a big amplitude change at the center and there is a fluctuation of the amplitude along the surface on the right half of the wavefield. This amplitude change along the surface can be explained by the aperture change along the surface caused by the irregular topography. The valley shape topography on the surface will have more aperture compared to the peak shape topography.

 

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Figure 9 Synthetic examples using the second scheme. (a) : Wave field recorded at the depth level at the bottom of the irregular topography. (b) : Wave field recorded at the irregular surface. (c) : Wave field extrapolated back to the bottom of the topography during the migration. (d) : The subsurface image obtained by the migration of the data in Figure (b). [ Compare to Figure . ]