echolocation
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Echiura. (Barnes 1987)
echolocation (syn. sound scanning) locates obstacles by emitting sound and
receiving and interpreting the echoes. Several species of bats and toothed
whales (including dolphins) have developed this system to a high degree of
perfection, while some other mammals, such as shrews, rats, seals, and penguins seem to use echoes to a lesser extent. The physical properties of water
allow sound to be propagated much more effectively than in air.
Echolocation has been found in more than ten species of toothed whales.
The sounds used are in the ultrasonic range (from 0.25 to 220 kHz). There is
growing evidence that the skulls of the marine echolocating species contain
several properties for emitting the sound in a narrow forward beam. Pulse
frequency increases when the predator closes in on its prey, both in whales
and bats.
echosounder, penetrating ~seismic instruments.
echosounding originally, a method of measuring the water depth. The depth is
measured by the travel time of acoustic signals, consisting of brief pulses of
sound between 20 and 200 kHz to the sea floor and back. Because of differences in temperature and salinity the acoustic velocity differs regionally.