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### Preprocessing

For each reflecting point and azimuth, rays corresponding to the same opening angle on opposite sides of the normal are linked together as dual rays. Rays whose emergence point (or that of its dual) fall outside the permit area for sources and receivers are discarded. Also discarded are rays for which the total traveltime is longer than the trace length. The remaining rays are assigned source or receiver positions according to the shortest distance between their emergence point and the closest source or receiver position for each geometry. Once a ray is classified as, say, source, its dual will be classified as receiver. Note that this classification is geometry-dependent. Figure  shows an example of the classification of a ray and its dual for two candidate geometries. The classification is done for all valid rays and the total distance that the emergence points have to be moved to conform with each geometry is recorded and saved. Minimizing this distance is equivalent to maximizing uniformity of illumination.

classify2
Figure 7
Classification of ray emergence points as sources or receivers. Vertical lines are source lines and horizontal lines are receiver lines. Two geometries are represented. The left panel illustrates a sparse geometry for which the ray in the top left would be classified as a source. The right panel shows the same ray which will now be classified as a receiver for this less sparse geometry.

For each geometry, I compute and save all the relevant parameters such as fold of coverage, maximum and minimum maximum offsets, aspect ratio, number of receiver per patch, etc. This information is saved and will be used as geophysical constraints for the optimization as described below. I also compute all relevant statistics of each geometry, such as number of sources, number of receivers, and receiver- and source-line cuts. This information is used to apply logistic constraints to the optimization. The cost of the survey, in particular, may largely depend on those statistics.

Next: Geophysical Constraints Up: Geometry Optimization Previous: Geometry Optimization
Stanford Exploration Project
7/8/2003