Glossary

Terms used in the acquisition calculator

Coverage - a measure of illumination
The area on the subsurface that is covered by a single pass of the acquiring vessel(s) in the crossline (xline) direction. Coverage is equivalent to half the width of the streamer spread, ignoring any distortions due to geological formations.

Fold
The number of traces that are collected within a single subsurface bin after the vessel(s) and the full recording spread have passed over it. All traces with a midpoint (between source and receiver) in the same bin are gathered together. This constitutes the fold for that bin.

Shot point interval
The distance between two shots from the same source. For dual and triple source modes, this distance will be larger than the pop interval. In dual source mode, the source activation normally alternates between sources (flip-flop) and the shot point interval refers to every second shot along the sail line (flip - flip).

Sail line spacing - a measure of efficiency
The distance between two adjacent vessel passes (xline direction). To ensure continuous coverage, sail line spacing will depend on the subsurface coverage at each pass.

Pop interval
The distance between any two adjacent source activations. This is the distance covered between two consecutive shots along the sail-line which are not necessarily from the same source. In dual source mode, the source activation normally alternates between sources, and the pop interval refers to each activation along the sail line (flip-flop).

Traces - a measure of the density of coverage
These are seismic recordings from each receiver group along the streamers. Often the terms traces and receivers are used interchangeably so that each receiver position at which data are collected will be called a trace. A multitude of traces will constitute seismic data. By plotting seismic traces next to each other, and processing the data, it is possible to generate an image of the subsurface.

Xline bin width - a measure of data quality
The xline (crossline) bin width is the size of each bin on the subsurface. This is perpendicular to the travel direction of the vessel. In 3D seismic, sampling is described by bins. The xline bin width describes the extent of these finite areas in the crossline direction and is a function of streamer spacing and source mode.

 

dual versus triple sourceThe illustration shows the source-streamer ray path contributions to each subline (i.e. CMP location) for dual-source shooting with 100 m streamer separation vs. triple-source shooting with 150 m streamer separation. In both scenarios, source separation is 50 m and crossline bin width (subline separation) is 25 m. The black diamonds represent the streamers and the blue rectangles represent sources. The crossline subsurface illumination is illustrated by the horizontal illumination bar at the bottom.