History
The SOFAR channel (short for sound fixing and ranging channel), or deep sound channel (DSC), 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 before dissipating. This phenomenon is an important factor in submarine warfare. The deep sound channel was discovered and described independently by Dr. Maurice Ewing, and Leonid Brekhovskikh in the 1940s.
Despite the use of the SOFAR channel in naval applications, the idea that animals might make use of this channel was not proposed until 1971. Roger Payne and Douglas Webb calculated that before ship traffic noise permeated the oceans, tones emitted by fin whales could have traveled as far as four thousand miles and still be heard against the normal background noise of the sea. Payne and Webb further determined that, on a quiet day in the pre–ship-propeller oceans, fin whale tones would only have fallen to the level of background noise after traveling thirteen thousand miles, that is, more than the diameter of the Earth.
Read more about this topic: Marine Mammals And Sonar
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