Seismic velocities - a critique
Techniques for estimating the velocity in the ground are almost as old as the seismic method itself - be it reflection or refraction. The geophysicist working on singlefold data made considerable use of such techniques as the T²_X² and T-AT methods, for velocity estimation, throughout the pre-digital processing era (see, for example Steele, 1941). Sometimes, a special shotpointgeophone arrangement using a field outlay that resembled a present-day CMP configuration was shot, with the objective of obtaining velocity estimates to successive reflectors (e.g. Gardner 1947). The process of velocity estimation was carried out manually, usually by means of graphical plots. These techniques culminated in the work of Dix (1955) which, being designed in common depth point geometry fashion, became directly applicable to multi-fold data when these became commonplace shortly afterwards.