Imaging of primaries

Shot-profile migration aims to produce an image of the subsurface by extrapolating both the source and receiver wavefields into the interior of the earth. The imaging condition () consists of crosscorrelating the two wavefields at each depth-step. Reflectors are formed where the two wavefields correlate. Figure illustrates this principle.

 

updown
Figure 1 The up-going wavefield is recorded everywhere at the receiver locations (shown as triangles). The down-going wavefield is emitted at the source location in the center of the survey (shown as a star). At earth location P1, the two extrapolated wavefields do not crosscorrelate because the down-going wavefield arrives at a much earlier time than the up-going wavefield. At earth location P2, which is the reflector depth, the two wavefields crosscorrelate and an image is formed. Adapted from Claerbout .

In general shot-profile migration is performed in the (2#2,x) domain one frequency at a time and one shot at a time. The final image is formed by adding all the different contributions of every shot together.