Angle-gather time migration

Velocity sensitivity

When dealing with real data we almost never know what the true velocity of the subsurface is. Therefore it is important to understand the effects of velocity on our angle-gather time migration algorithm. To do this we simply created data for the dome model in Figure 4 at a fairly high velocity (3 km/s) and migrated it using a low velocity (1.5 km/s). The results are in Figure 11. For angles less than the maximum useful angle ( $\gamma=25^{\circ}$), the angle-domain gather behaves exactly as the offset-domain gather does. Beyond the maximum useful angle, the events become even more curved and the amplitudes begin to change.

The behavior of the angle-gather migration is very similar to that of offset-domain migration as long as the limitation of the maximum useful angle is recognized. Therefore, we can probably expect angle-gather migration to behave like offset-domain migration in $v(z)$ media also.

agather-dome-fast
Figure 11. Gathers taken from space location zero inthe dome model and migrated at too low a velocity. Left: Offset domain. Center: Angle domain less than $25^{\circ }$. Right: Angle domain.

Angle-gather time migration