Page 131 - Acquisition and Processing of Marine Seismic Data

122 2. MARINE SEISMIC DATA ACQUISITION

FIG. 2.75 Coverage area for one single shot in 3D case. Coverage areas for (A) four- and (B) eight-streamer acquisitions. Red
dashed lines correspond to CMP lines obtained from each streamer.

streamer separations result in a smaller bin size, the early 1980s, 12.5 m 50 m inline and cross-
and therefore provide a better spatial resolution. line bin sizes were typical. By the introduction of
Acquisition with a fan mode shooting layout dual source flip-flop acquisition and smaller
(Section 2.3.7) can further increase the crossline streamer separations, inline and crossline bin
coverage, especially for long offsets, which can sizes were reduced to 6.25 m 12.5 m,
reduce the shooting times for additional respectively.
infill areas. In 3D marine surveys, bin size is governed by
the geometry of the spread. Inline bin size is typ-
2.5.1.7 Bin Size ically chosen as one-half of the group interval
A CDP bin is a square or rectangular area con- both for 2D and 3D acquisition. Crossline bin
taining several traces radiated from different size is, however, controlled by a number of fac-
sources and recorded at different receivers, tors, such as number of streamers, streamer sep-
but all of which have the same midpoints aration, and number of sources. Incorporation of
(Chapter 8). Bin size represents the length and dual source doubles the number of CDP lines
width of the rectangular or square-shaped and reduces the crossline bin size by half. In con-
CDP bin, and depends on the target size, spatial ventional dual source 3D acquisition, source
resolution needed, and the cost of the survey. In separation is half of the streamer separation,