Time to depth conversion

One can use image-ray corrections to convert a migrated time-section to a depth-section (Larner et al., 1981). The image-rays are rays that have vertical incident angles at the surface. Usually, the trajectories of these rays are calculated by ray tracing. The conventional one-point ray tracing method can set the starting points of the rays. However, it can not control the destinations of the image-rays. Therefore, the converted depth-image has to be interpolated. For complicated velocity models, rays may not penetrate shadow zones; the interpolation is thus cumbersome. Using the two-point ray tracing described in this paper, one can trace image-rays to any imaging points. The interpolation is done in the input time-section that is uniformly sampled. In Figure , I show the image-rays calculated with the fast two-point ray tracing algorithm. The destinations of these rays are uniformly distributed along the bottom of the slowness model.

 

ttod
Figure 4 Image-rays with uniformly spaced destinations. The background shows the slowness model. High intensities denote high velocities or low slowness.