Redatuming is applied early in the processing flow and it will affect all subsequent processing. Proper redatuming to a flat surface is crucial for algorithms which assume hyperbolic form, such as velocity analysis. It is also advantageous because the most efficient DMO and migration algorithms assume a flat, regularly-sampled processing datum. Since the datuming velocity is known, it can be incorporated into the prestack migration velocity field so that when the data are migrated from the flat datum, the effect of the datuming is counteracted.
In the example I presented in this chapter, I showed that upward continuing the data to a flat regularly sampled processing datum with Kirchhoff datuming is superior to elevation statics. It offers a relatively painless way of obtaining a preliminary structural image that does not require a detailed knowledge of the subsurface velocity distribution. This is because stacking and migration velocities are more accurately and easily determined without the unnecessary complication of nonhyperbolic distortion, which would arise if the data were processed from the topography or after elevation statics.