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The subsurface model is used to trace rays up to the surface from points on
the reflectors of interest at finely-sampled opening (polar) and azimuth
angles. The
number and location of the reflecting points on the reflectors of interest,
as well as the number of rays shot from each such point, is a matter of design.
The important point is that they represent our ideal subsurface illumination
response. Departures from this ideal will be penalized in the optimization
process. For this paper I used the Integra software to do the ray tracing.
I used Gocad to compute a stratigraphic grid draped over the target reflector
(Figure ) and used the grid centers as the starting points for
the rays. The grid is 25 x 25 m and 20 rays were shot from each point. The range
of azimuths was from 0 to 135 degrees in intervals of 45 and the range of
opening angles was from 0 to 60 degrees in intervals of 15 degrees.
Figure shows ray cones emanating from a few selected
points on the target horizon's surface.
**rays1
**

Figure 6 Exploding reflector rays. Rays from a few of
the reflecting points on the target horizon. There are several
thousand such reflecting points, so the resulting density of rays is very large.

Integra ray tracing program computes, for each ray, its travel time and the
coordinates of the emerging point at the surface. The program also records the
coordinates of the normal to the reflector at the starting point, as well as
the opening and azimuth angle of the corresponding ray. In the present
example I used this information to separate the rays originating at different
depths in the target reflector.

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** Up:** The Proposed Approach
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Stanford Exploration Project

7/8/2003