Sofar channel

From Wikipedia, the free encyclopedia

SOFAR channel stands for "SOund Fixing And Ranging channel". It is a layer of water deep in the ocean (near Bermuda it's around 1000 metres deep) where the speed of sound is at a minimum. This minimum sound speed exists at the depth where the cumulative effect of water pressure, temperature, and salinity causes the water at this depth to be less dense than that of other parts of the water column.

Within the SOFAR channel, low frequency waves may travel hundreds, if not thousands, of miles before dissipating. In temperate waters, this minimum sound depth is shallower, and it reaches the surface between about 60 degrees N or 60 degrees S.

This phenomenon is due to the refractionary tendencies of sound that makes it travel at the depth of its slowest speed (if a sound wave is drifting away from this horizontal channel, the part of the wave that is closer to the center of the SOFAR channel slows down and causes the wave to "turn" back to the slower depth).

Strange and mysterious low-frequency sounds, attributed to humpbacks and other baleen whales, are a common occurrence here. Scientists think that humpback whales may dive down to this channel and "sing" to communicate with other humpback whales many kilometers away.

During World War II, Maurice Ewing suggested that dropping a small metal sphere into the ocean, specifically designed to implode at the SOFAR channel, could be used as a secret distress signal by downed pilots. ^[1]

The novel The Hunt for Red October describes the use of the SOFAR channel in submarine detection.