Strike versus dip shooting
It is interesting to raise the question of which direction is better in recording — dip line or strike line, since we just noted that crossline smearing is most severe when shooting in the strike direction. Both types have advantages and disadvantages.
Aspects of dip-line shooting are summarized below:
- With dip-line shooting, you have a better spatial sampling in the direction that you need most.
- Since there is no cross-dip, there is no crossline smearing, and you can afford coarser spacing between lines.
- With dip-line shooting, you have the disadvantage of complex moveout on common-cell data that can cause problems in velocity analysis .
- You also have the problem of inline smear because of the reflection point dispersal along the dipping reflector associated with a nonzero-offset recording (Section E.1). Nevertheless, DMO correction handles this problem.
Aspects of strike-line shooting are summarized below:
- With strike-line shooting, you have better attenuation of coherent noise because of the moveout behavior of side scatterers.
- Since there is no dip perceived on a strike line, in principle, you do not need DMO correction.
- With strike-line shooting, however, you have the disadvantage of perceiving the largest cross-dip, hence you would have the problem of crossline smear to deal with.
- More importantly, strike-line shooting would require closer line spacing to prevent spatial aliasing of steep dips in the orthogonal direction; otherwise trace interpolation becomes important.
Among these various factors, adequate spatial sampling of steep dips is a requirement that takes precedence over the others. This means that, given the choice between the two types of shooting, dip-line shooting must be employed almost always in data acquisition. Nevertheless, modern 3-D surveys are conducted using sufficiently small inline and crossline spacings which more than accommodate the requirements for adequate spatial sampling of steep dips, minimizing crossline smearing and accurate implementation of 3-D DMO correction for removing inline smearing.
- Larner and Ng, 1984, Larner, K. and Ng, P., 1984, Strike versus dip shooting: 53th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, 256–260.
- Migration aperture
- Spatial sampling
- Other considerations
- Marine acquisition geometry
- Cable feathering
- 3-D binning
- Crossline smearing
- Land acquisition geometry