Directivity of marine arrays
Figure 8.9a shows the directivity effect of group length typical of end-on marine shooting. How will the curves change (a) with arrival time, (b) as offset increases, and (c) for greater stacking velocity? Is it better to tow the recording system in the updip or the downdip direction?
Aside from the effects of the number and spacing of the elements, angles of approach, and wavelength, the array response is affected by NMO and dip moveout. These add in the downdip direction and subtract in the updip direction.
- As increases, the NMO decreases and hence has less effect, so the curves in Figure 8.9a become more symmetrical.
- As the offset increases, the NMO increases and the curves become more asymmetrical.
- For greater stacking velocity, NMO decreases and the curves become more symmetrical.
Because NMO and dip moveout effects add in the downdip direction, it is better to shoot in the updip direction.
|Previous section||Next section|
|Tapered arrays||Response of a triangular array|
|Previous chapter||Next chapter|
|Seismic equipment||Data processing|
Also in this chapter
- Effect of too many groups connected to the cable
- Reflection-point smear for dipping reflectors
- Stacking charts
- Attenuation of air waves
- Maximum array length for given apparent velocity
- Response of a linear array
- Directivities of linear arrays and linear sources
- Tapered arrays
- Directivity of marine arrays
- Response of a triangular array
- Noise tests
- Selecting optimum field methods
- Optimizing field layouts
- Determining vibroseis parameters
- Selecting survey parameters
- Effect of signal/noise ratio on event picking
- Interpreting uphole surveys
- Weathering and elevation (near-surface) corrections
- Determining static corrections from first breaks
- Determining reflector location
- Blondeau weathering corrections