...point

This is a simplification: if the earth has a strong velocity gradient with depth, the seismic energy will actually overturn and simple downward continuation will not move the energy to its true reflection point. This energy becomes evanescent and disappears.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

...velocities

This DSR equation is a simplification of what is done in practice. Algorithms for downward continuation require so-called reference velocities to be picked for each depth step rather than using the ``true'' velocities and interpolation. These migration schemes are known as Phase Shift Plus Interpolation ().

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

...times

Note that the cost of generating the model space weighting operator is equal to two migrations and is applied to a migrated image, making the total cost equal to three migrations. The regularized inversion has a cost of two migrations for each iteration, making the total cost equal to twenty migrations.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.