Statistical measures of subsurface illumination

The field geometry employed in 3-D seismic data acquisition is critical in determining the resulting pattern of subsurface illumination. Complex geology has long been recognized to destroy uniform subsurface illumination. More recently, 3-D geometries have been shown to have systematic illumination difficulties for the simple case of homogeneous media (Beasley and Mobley, 1995; Egan and Dingwall, 1991; Slawson et al., 1995; and Vermeer, 1994). Clearly, there is a need to comprehend the effects of geometry on subsurface illumination in a concise and efficient manner. One approach involves ray tracing through a specified geologic model using the actual geometry of the sources and receivers. Within the accuracy of the ray tracing, complex geology can be incorporated in the analysis. However, the results are sensitive to the particular geologic model - small changes in the model can create large changes in the estimate of the illumination pattern. Another drawback to this approach is that the inherent high cost of nonzero-offset ray tracing limits the scope of the analysis.