An algorithm for estimating velocity

We estimate velocity by iteratively migrating the prestack data and looping through the following steps:

1.

Downward continuation with current velocity,

2.

Extraction of common-image gathers from prestack wavefields Prucha et al. (1999),

3.

Residual prestack migration of common-image gathers,

4.

Estimation of image perturbation from the results of residual prestack migration, and

5.

Estimation of velocity perturbation from image perturbations.

The core technical element of the method is the estimation of velocity perturbations from image perturbations. The next section presents the linear theory that enables us to achieve this goal.