Common shot gather imaging is done because the shot-geophone coordinate system
is probably the best system in which to work when trying to estimate a laterally
varying velocity function. Shot-geophone coordinates also have advantages when
the shot axis is aliased. Within a shot gather, the data is a function of time
and offset. Migration is easier after NMO correction and a time-to-depth con-
version, since all that is involved is the application of small shifts to the
dipping events in the moveout corrected gather. These shifts are in both the
vertical and lateral directions. A natural coordinate system for describing an
NMO and time-to-depth corrected gather is the radial/NMO coordinate system.
STANFORD