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seismic instruments
seismic instruments the instruments and sources of energy used in marine seismic
surveys are numerous and depend upon the particular purpose. The study of
the deepest layers and the Moho requires seismic refraction shooting with explosive charges of up to 100 kg TNT. The more frequently used seismic reflection
shooting can do with smaller acoustic pulses and as conventional chemical
explosives are highly impractical, a wide variety of nonexplosive sources has
been developed. One of the larger energy sources used in marine seismic
reflection work is the air gun, a device which functions by discharging a bubble of highly compressed air into the water. The water gun uses the discharge
of compressed air to drive a piston. The piston displaces a body of water at
such a speed that a vacuum cavity forms in the water. The implosion of the
vacuum cavity generates the seismic pulse. The weaker sources include the
boomer, the sparker, and the penetrating echosounder. The boomer generates an acoustic wave by implosion. It consists of two metal plates which are
electrically forced apart, producing a low pressure region into which water
rushes. The sparker creates a spark between electrodes located in the water.
The heat created by the spark vaporizes the water, creating an effect equivalent to a small explosion. A penetrating echosounder is a low-frequency
echosounder (often 3.5 kHz) which is able to penetrate into the upper sediHIgh-pm",,..
r
Port
8
Air gun: see seismic instruments. (After Dobrin 1976)
seismic instruments
seismic instruments the instruments and sources of energy used in marine seismic
surveys are numerous and depend upon the particular purpose. The study of
the deepest layers and the Moho requires seismic refraction shooting with explosive charges of up to 100 kg TNT. The more frequently used seismic reflection
shooting can do with smaller acoustic pulses and as conventional chemical
explosives are highly impractical, a wide variety of nonexplosive sources has
been developed. One of the larger energy sources used in marine seismic
reflection work is the air gun, a device which functions by discharging a bubble of highly compressed air into the water. The water gun uses the discharge
of compressed air to drive a piston. The piston displaces a body of water at
such a speed that a vacuum cavity forms in the water. The implosion of the
vacuum cavity generates the seismic pulse. The weaker sources include the
boomer, the sparker, and the penetrating echosounder. The boomer generates an acoustic wave by implosion. It consists of two metal plates which are
electrically forced apart, producing a low pressure region into which water
rushes. The sparker creates a spark between electrodes located in the water.
The heat created by the spark vaporizes the water, creating an effect equivalent to a small explosion. A penetrating echosounder is a low-frequency
echosounder (often 3.5 kHz) which is able to penetrate into the upper sediHIgh-pm",,..
r
Port
8
Air gun: see seismic instruments. (After Dobrin 1976)