PSPI 3D One Pass Migration
Theory
Performs 3D migration on 3D stacked seismic data, using phase-shift migration modified by correction plus interpolation for spatial velocity variations.
The program first processes velocity. The input velocity functions should be in RMS format. After time interpolation, the program transfers the RMS function to interval velocity VIT, then it performs velocity spatial interpolation for all CDPs. After this step, the program will apply a velocity smoother in spatial domain adjusted by the smoother value the user has chosen. A velocity disk file that has the same time interval as the migration time interval is written to the SCRATCH area.
Vertical and spatial velocity variations are managed very well by this algorithm. The program can use up to 3 velocity references, which works well for most surveys. For each velocity reference, the program uses phase-shift migration modified by first-order correction to each CDP velocity value. So, even when using one velocity reference, the results will be better than that of phase-shift migration and FK migration. When using more than one velocity reference, the program will perform migration plus correction plus interpolation, which will coincide better with spatial velocity variations. The results will be smoother and have greater resolution than the result when using 1 reference.
The time interval for migration could be several times the sample interval, depending on the dip degrees the user inputs in the post migration section. A smaller degree will reduce the run-time significantly. Migration works on frequency (time to frequency) domain, but after several migration steps, the migration trace will be shorter than the original trace length to save run-time. The original trace length still affects the run-time.