Page 82 - Acquisition and Processing of Marine Seismic Data

2.2 AIR GUN ARRAYS 73

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FIG. 2.30 Far-field signatures of a 3190 in array with (A) only source ghost and (B) source and receiver ghost interference.
Their corresponding amplitude spectra are given in (C) and (D), respectively. Since source and receivers are towed at different
depths, they have their own ghost notches appearing at different frequencies in the amplitude spectrum. R 1 and R 2 are the
receiver notches, while S 1 and S 2 represent the source notches.

elements in the array, the air pressure applied to In an air gun array, individual guns are in
the guns, and the total gun volume of the array. weakly or strongly interacting positions based
An array with 20 guns produces two times on the distance between them. If two or more
larger amplitude than an array with 10 air guns. guns are positioned with a lateral distance
In practice, the number of guns in the array is the slightly less than or equal to one meter, the array
most efficient parameter on the resultant pri- is termed strongly interacting. If the separation
mary amplitude. The output amplitude is is more than approximately 1 m between two
almost directly proportional to the operation successive guns, then the array is termed weakly
pressure, and an array with 3000 psi pressure interacting. The gun groups with a lateral sepa-
produces almost 1.5 times larger amplitude than ration of approximately 1 m are named clusters.
an array operating at 2000 psi pressure. Finally, In the last two decades, array designs with sev-
the amplitude is directly proportional to the eral strongly interacting guns or gun clusters
cubic root of the total gun volume of the array. have become very popular and a modern gun