Processing of PP data
The next step in processing of the 4-C seismic data is to calibrate the vertical geophone component Z(t) and sum it with the hydrophone component P(t) to obtain the total PP data. This dual-sensor summation is done to remove water-column reverberations . Calibration may involve just a single scalar applied to the entire geophone data prior to summation with the hydrophone data. More sophisticated calibration techniques include the application of surface-consistent scalars computed for each receiver location or application of surface-consistent scalars computed for each receiver location and for each frequency component   .
The merged PP data are now ready for conventional processing. First, apply a vertical time shift that is equal to the water depth divided by water velocity to bring the receivers from the seabed to the same datum as the shots. If the water depth is greater than 100 m, the vertical shift may not be valid; instead, the datuming may have to be done by wave-equation datuming (layer replacement).
The remaining prestack processing sequence for the PP data is no different from the land data processing sequence and includes geometric spreading correction, deconvolution, refraction and residual statics corrections to account for the variations in the seabed geometry, velocity analysis, NMO and DMO corrections. The poststack processing sequence typically includes deconvolution, time-variant filtering, and migration. Shown in Figure 11.6-20 is a CMP gather associated with the PP data as in Figure 11.6-14. The CMP stack is shown in Figure 11.6-21. The average fold of coverage is 150.
Figure 11.6-20 A CMP gather from the PP-data as in Figure 11.6-14 and the semblance spectrum for PP-velocity analysis. (Processing by Orhan Yilmaz, 1999).
- Barr and Sanders, 1989, Barr, F. J. and Sanders, J. I., 1989, Attenuation of water-column reverberations using pressure and velocity detectors in a water-column cable: 59th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 653–656.
- Dragoset and Barr, 1994, Dragoset, W. and Barr, F. J., 1994, Ocean-bottom cable dual-sensor scaling: 64th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 653–656.
- Paffenholz and Barr, 1995, Paffenholz, J. and Barr, F. J., 1995, An improved method for deriving water-bottom reflectivities for processing dual-sensor ocean-bottom cable data: 65th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 987–990.
- Soubaras, 1996, Soubaras, R., 1996, Ocean-bottom hydrophone and geophone processing: 66th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 24–27.
- 4-C seismic method
- Recording of 4-C seismic data
- Gaiser’s coupling analysis of geophone data
- Rotation of horizontal geophone components
- Common-conversion-point binning
- Velocity analysis of PS data
- Dip-moveout correction of PS data
- Migration of PS data