Till now, we have limited our data processing to midpoint-offset space. We have not analyzed reflection data directly in shot-geophone space. In practice this is often satisfactory. Sometimes it is not. The principal factor that drives us away from (y,h)-space into (s,g)-space is lateral velocity variation .In this chapter, we will see how migration can be performed in the presence of v(x,z) by going to (s,g)-space.
Unfortunately, this chapter has no prescription for finding v(x,z), although we will see how the problem manifests itself even in apparently stratified regions. We will also see why, in practice, amplitudes are dangerous.