Acoustic surveys, marine
Reference work entry
Marine acoustic surveys represent one of several geophysical techniques commonly used to delineate and study the character and structure of the ocean bottom and subbottom. In acoustic surveys (see Vol. I, Acoustics, Underwater), sound energy is transmitted through seawater to the ocean bottom or subbottom where it is reflected off the sea bottom and received by the ship through listening devices called hydrophones. The time period required for the sound to travel to the reflecting surface and back to the ship is a function of the distance to the reflecting surface. Because most acoustic survey systems provide continuous operation, surveys are normally operated at a ship speed of 10–12 nautical miles per hour (1 nautical mi = 1,852 m), and a continuous profile of the reflecting surface is produced on board the ship by a graphic recorder ( Figure 1).
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