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Acoustical "vision" underwater

When we (and all eyed animals) see an object, we are detecting light reflected from that object. When underwater, though, our vision is limited because light does not travel far. Sound, however, does; and sound is reflected from objects just as light is. This is of course the basis of underwater sonar, in which a sound source replaces the sun or a diver's floodlight. But even without an active sound source, the ocean is full of sound. Waves, rain, and the sounds made by marine animals create a background of noise that "illuminates" objects, not directly, but from the environment in general. Using only this enveloping background sound, it is possible to create acoustical images of objects. "Vision" of this sort is equivalent to "facial vision" in blind humans, who can hear objects using the environmental sound reflected from them.

J. Potter and his colleagues at the National University of Singapore have constructed an array of underwater microphones that detects "slices" of the acoustical environment around it. When processed by a computer, images of objects emerge by virtue of the background noise reflected from them.

This group has also estimated the ability of dolphins to detect and process background noise. They suggest that dolphins should be able to "see" objects at least 25 feet away without even using their active sonar; that is, their clicks. This passive acoustical imaging would be a useful evolutionary development because dolphin clicks warn some prey and allow them to escape.

(Anonymous; "Cacophony of the Deep," Discover, 19:19, May 1998.)

Comments. Some insects can detect the sonar cries of pursuing bats and take evasive action. Perhaps some fish can detect pursuing dolphins, too.

Blind people can augment facial vision by tapping with a cane or using a mechanical clicker.

From Science Frontiers #120, NOV-DEC 1998. 1998-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:

Quotes

  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987