Common-offset migration of DMO-corrected data
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This technique for migration velocity analysis is the basis for the most common sequence used for prestack time migration (prestack time migration). A flowchart for the method is shown in Figure 5.4-4.
- Starting with prestack data P(y, h, t) in coordinates of midpoint y, offset h, and two-way event time t in the unmigrated position, apply NMO correction using an initial velocity field with minimal dip effect.
- Sort the normal-moveout corrected data P(y, h, tn) to common-offset sections P(y, tn; h).
- To each common-offset section P(y, tn; h), apply DMO correction P(y, τ0; h).
- Migrate each of the common-offset sections using a zero-offset migration algorithm (migration) and the velocity field based on the flat-event velocity picks from step (a).
- Sort the migrated common-offset data P(y, τ; h) back to CMP gathers P(y, h, τ) and apply inverse NMO correction using the flat-event velocities from step (a).
- Perform velocity analysis at frequent intervals as needed to derive an optimum velocity field which is used for the subsequent migration of the data.
- Prestack Stolt migration
- Prestack Kirchhoff migration
- Velocity analysis using common-reflection-point gathers
- Focusing analysis
- Fowler’s velocity-independent prestack migration