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Line 27: − The output of an air gun array is typically illustrated by a normalized pressure time sequence called a ''signature''. The signature of a 1000-in.<sup>3</sup> air gun subarray is shown in Figure 1. One measure of the strength of the source is the ''peak-to-peak pressure'', which is often quoted in pressure units of bars at [[length::1 m]] (bar meters). Another measure of the performance of the array is the ''peak-to-bubble ratio'', which is the peak-to-peak magnitude of the initial pulses divided by the magnitude of the residual bubble oscillations. These simplistic measures of performance can be used to compare different sources provided the signatures have been recorded using the same techniques, especially the same field filters<ref name=pt07r24>Johnston, R. C., Reed, D. H., Desler, J. F., 1988, SEG standards for specifying marine seismic energy sources: Geophysics, v. 53, p. 566–575., 10., 1190/1., 1442492</ref>.+ − − − + − +
Marine seismic data acquisition (view source)
Revision as of 18:56, 17 January 2014
, 18:56, 17 January 2014→Source
==Source==
==Source==
[[file:marine-seismic-data-acquisition_fig1.png|thumb|{{figure number|1}}Typical air gun array signature.]]
Over the years, a large variety of different marine seismic energy sources have been used, but today two sources are used for almost all of the marine seismic shot. These are the air gun and the water gun, with the air gun being by far the most common.
Over the years, a large variety of different marine seismic energy sources have been used, but today two sources are used for almost all of the marine seismic shot. These are the air gun and the water gun, with the air gun being by far the most common.
Recently, ''sleeve guns'', which are designed to be more efficient and reliable than conventional air guns, have been introduced. A disadvantage of the sleeve gun is that it is currently offered in only a few discrete sizes, which handicaps the air gun array designer. ''Clustered guns'' are another recent advancement. When two or three air guns are fired in close vicinity of one another, it is possible to get a strong initial pulse and a weak bubble sequence because the composite bubble formed is not spherical and thus does not tend to support oscillations.
Recently, ''sleeve guns'', which are designed to be more efficient and reliable than conventional air guns, have been introduced. A disadvantage of the sleeve gun is that it is currently offered in only a few discrete sizes, which handicaps the air gun array designer. ''Clustered guns'' are another recent advancement. When two or three air guns are fired in close vicinity of one another, it is possible to get a strong initial pulse and a weak bubble sequence because the composite bubble formed is not spherical and thus does not tend to support oscillations.
[[file:marine-seismic-data-acquisition_fig2.png|thumb|{{figure number|2}}Air gun array strength.]]
[[file:marine-seismic-data-acquisition_fig1.png|thumb|{{figure number|1}}Typical air gun array signature.]]
The strength of marine seismic sources has increased at a steady pace over the past 20 years, as shown in Figure 2. Stronger sources produce detectable signals from deeper reflectors. Very large air compressors are necessary to charge the air guns, which typically fire every 10 sec. In addition to increased strength, air gun arrays consisting of six, eight, or ten subarrays (''strings'') are deployed in various geometries to improve directivity and/or to reduce shot generated noise. The simple wide array is common and very effective<ref name=pt07r35>Lynn, W., Larner, K., 1989, Effectiveness of wide marine seismic source arrays: Geophysical Prospecting, v. 37, p. 181–207., 10., 1111/gpr., 1989., 37., issue-2</ref>.
The output of an air gun array is typically illustrated by a normalized pressure time sequence called a ''signature''. The signature of a 1000-in.<sup>3</sup> air gun subarray is shown in [[:file:marine-seismic-data-acquisition_fig1.png|Figure 1]]. One measure of the strength of the source is the ''peak-to-peak pressure'', which is often quoted in pressure units of bars at [[length::1 m]] (bar meters). Another measure of the performance of the array is the ''peak-to-bubble ratio'', which is the peak-to-peak magnitude of the initial pulses divided by the magnitude of the residual bubble oscillations. These simplistic measures of performance can be used to compare different sources provided the signatures have been recorded using the same techniques, especially the same field filters<ref name=pt07r24>Johnston, R. C., Reed, D. H., Desler, J. F., 1988, SEG standards for specifying marine seismic energy sources: Geophysics, v. 53, p. 566–575., 10., 1190/1., 1442492</ref>.
[[file:marine-seismic-data-acquisition_fig2.png|thumb|{{figure number|2}}Air gun array strength.]]
The strength of marine seismic sources has increased at a steady pace over the past 20 years, as shown in [[:file:marine-seismic-data-acquisition_fig2.png|Figure 2]]. Stronger sources produce detectable signals from deeper reflectors. Very large air compressors are necessary to charge the air guns, which typically fire every 10 sec. In addition to increased strength, air gun arrays consisting of six, eight, or ten subarrays (''strings'') are deployed in various geometries to improve directivity and/or to reduce shot generated noise. The simple wide array is common and very effective<ref name=pt07r35>Lynn, W., Larner, K., 1989, Effectiveness of wide marine seismic source arrays: Geophysical Prospecting, v. 37, p. 181–207., 10., 1111/gpr., 1989., 37., issue-2</ref>.
==Receiver==
==Receiver==