Page 132 - Acquisition and Processing of Marine Seismic Data

2.5 DATA ACQUISITION PARAMETERS 123

FIG. 2.76 (A) The separation between the CMP lines is one-half of the streamer separation for single source 3D acquisition.
(B) In dual source flip-flop acquisition, the separation between the CMP lines is one-quarter of the streamer separation.

so that the crossline bin size is one-quarter of the especially for the migration process. If the bin
streamer interval. In a theoretical sense, the size is too large, the subsurface is too coarsely
length of the bin may equal to the radius of sampled, which ultimately results in aliasing
the Fresnel zone, which is defined as the area of the higher frequencies. In practice, bin size
on a subsurface reflector that reflects the energy should be small to ensure the high lateral resolu-
arriving at the receiver within a time delay equal tion, which significantly improves the seismic
to half the dominant period. The radius of the image quality. Widely spaced streamers in 3D
Fresnel zone is expressed by surveys result in larger bin sizes, while smaller
spacing between the hydrophone group centers
s ffiffiffiffi
V RMS t 0 and between the streamers provides denser
r ¼ (2.3)
2 f trace spacing and higher resolution data,
although it will reduce the total swath width
where V RMS is the average RMS velocity down or spatial coverage, which requires more closely
to the target depth, f is the dominant frequency spaced sail lines and increases the overall
of the seismic signal, and t 0 is the two-way survey time.
travel time. Fig. 2.77 shows a comparison of two 3D
The bin size will affect the spatial resolution seismic datasets with different bin sizes. The
of the survey: it should be small enough to avoid line in Fig. 2.77A was collected with four
spatial aliasing during the processing stage, streamers of 53.3 m separation and a single