** Next:** THE ESTIMATION RESULTS
** Up:** Biondi: Velocity from beam
** Previous:** DESCRIPTION OF THE DATA

The velocity-estimation method that I described in previous reports
(Biondi, 1989; Biondi, 1988) is based on the
maximization of beam stacks' energy
at the traveltimes and surface locations predicted by the velocity function
and modeled with raytracing.
Therefore in order to estimate the velocity,
I computed beam stacks from the prestack data for 12 offset ray parameters
*p*_{h}, from .05 s/km to .336 s/km,
and for three midpoint ray parameters
*p*_{y}, from -.04 s/km to .04 s/km.
I transformed the beam-stacks according to the coordinate transformation
introduced in the previous report (Biondi, 1989), assuming a constant
velocity of 2.5 km/s.
I then smoothed the transformed data along the midpoint axis
and the time axis using Gaussian windows.
The smoothed and transformed data from the
250 midpoint positions located around the anomaly were used
by the velocity estimation.
The starting solution for the iterative estimation algorithm was
a velocity profile function of depth, but constant
in the lateral direction.
This velocity function was derived from
conventional stacking velocity analysis applied to a few of the CMP gathers.
The estimation procedure started with few conjugate gradient iterations
until the velocity model predicted the gross feature of the beam-stacked
data, and then continued with some Gauss-Newton iterations
for better estimating the finer components of the velocity function.

** Next:** THE ESTIMATION RESULTS
** Up:** Biondi: Velocity from beam
** Previous:** DESCRIPTION OF THE DATA
Stanford Exploration Project

1/13/1998