Typical Seismic Profiling Operation

Air guns generate pulses of acoustic energy by the sudden release of highly compressed air. All 64 guns discharge within two-tenths of a milhsecond of each other. To someone on board, their combined sound is more felt than heard, a muffled bump, followed immediately by an echo (thump) returning from the ocean floor below the ship. 

Instantly the guns recharge for the next shot which comes 7-10 s later, depending on how deeply the client wishes to probe into the underlying strata. 

To pick up the sound signals, the ship streams in its wake a 3,000-m cable containing up to 7,680 hydrophones, each spaced 0.5 m apart. The hydrophones, each one about the size of a quarter, sense minuscule changes in pressure and transmit this information through a fiber-optic cable to the ship s recorders. Winglike devices, called birds, hold the cable at depths ranging from 3 to 6 m. A tail buoy marks its farthest extremity. 

Returning signals are detected by the hydrophones and forwarded to the ship s computer room. There, the incoming data are digitized and stored on a variety of electronic media. 

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