The unimpressive improvement in the image quality seems to
be due to two factors. First, the introduced slowness change
was too low in spatial frequency. The initial slowness model
was already well determined for features at this scale. In addition,
2-D tests showed that image quality was most improved
when allowing smaller scale changes to the velocity. Relaxing the
smoothness constraint (by both decreasing in fitting
goals (4) and iterating more) is called for. The
second weakness seems to be poor constraint of the lower portion
of the model. The obvious answer is to pick more reflectors.
Both of these changes have been made, but unfortunately time
constraints did not allow the results to be included in this paper.
Stanford Exploration Project