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The SOFAR channel (short for sound fixing and ranging channel), or deep sound channel (DSC), [1] is a horizontal layer of water in the ocean at which depth the speed of sound is at its minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating.
Underwater sound has probably been used by marine animals for millions of years. The science of underwater acoustics began in 1490, when Leonardo da Vinci wrote the following, [2] "If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from ...
Underwater communication is difficult due to factors such as multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. Compared to terrestrial communication, underwater communication has low data rates because it uses acoustic waves instead of electromagnetic waves.
Upsweep is an unidentified sound detected on the American NOAA's equatorial autonomous hydrophone arrays. This sound was present when the Pacific Marine Environmental Laboratory began recording its sound surveillance system, SOSUS, in August 1991. It consists of a long train of narrow-band upsweeping sounds of several seconds in duration each.
The SOFAR channel (short for "sound fixing and ranging channel"), or deep sound channel (DSC), [4] is a horizontal layer of water in the ocean centered around the depth at which the speed of sound is at a minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles ...
While terrestrial animals often have a uniform method of producing and detecting sounds, aquatic animals have a range of mechanisms to produce and detect both vocal and non-vocal sounds. [7] In terms of sound production, fish can produce sounds such as boat-whistles, grunts and croaks using their swim bladder or pectoral fin.
In underwater acoustics and fisheries acoustics the term is also used to mean the effect of plants and animals on sound propagated underwater, usually in reference to the use of sonar technology for biomass estimation. [2] [3] The study of substrate-borne vibrations used by animals is considered by some a distinct field called biotremology. [4]
A hydrophone can also detect airborne sounds but is insensitive of them because it is designed to match the acoustic impedance of water, a denser fluid than air. Sound travels 4.3 times faster in water than in air, and a sound wave in water exerts a pressure 60 times more than what is exerted by a wave of the same amplitude in air.