|"Sonar." Encarta's Encyclopedia Online. Microsoft, 2001.||"Modern ultrasonic generators can produce frequencies up to more than several gigahertz (1 GHz = 1 billion Hz)."||1 GHz|
|"Branch of physics dealing with high-frequency sound waves, usually in the range above 20,000 hertz (Hz)."||20 kHz|
|Shultz, Ken. Fishing book & Worldwide Angling Guide. 1st ed. 1999: 310.||"Frequencies for sport fishing sonar are 50 kHz and 200 kHz, although 120 kHz, 455 kHz, and other frequencies are also used."||50, 120, 200, 455 kHz|
|"Sonar." Columbia Electronic Encyclopedia, Sixth Edition. Columbia University Press, 2000.||"Sonar operates in the 10 to 50 kilocycle acoustical frequency range."||10–50 kHz|
|Fornari, Dan. High-Frequency Sonars. Woods Hole Oceanographic Institute (WHOI) Marine Operations.||"The DSOG now operates 120 kHz and 200 kHz split-beam sonar systems designed for deeply-towed, near-bottom seafloor imaging and swath phase-bathymetric mapping."||120, 200 kHz|
Sonar is a device that uses sound energy to locate objects; measure their distance, direction, and speed; and produce pictures of them. The word sonar comes from sound navigation and ranging. Sonar works well underwater, where sound travels quickly and efficiently over long distances and where radar does not work. However, certain sonar devices operate in the air. For example, some burglar alarms use airborne waves of ultrasound to detect movement. Dolphins and some bats use a natural sonar technique called echolocation. This technique helps them locate food, avoid obstacles, and communicate.
There are two types of sonar active and passive. Active sonar uses a transmitter, a device that converts electrical energy to sound energy, to send out sound waves. The sound waves travel through the water until they strike an object. The object reflects them in various directions. Some of the reflected waves return to the sonar, where they strike a receiver. Sonar determines distances by measuring the time taken for a sound wave to travel from the transmitter, reflect from the object, and travel to the receiver.
Passive sonar receives sound waves given off by some other source, but does not transmit sounds. Passive sonar can therefore determine the direction of an object, but is not as effective as active sonar in determining its distance.
Some uses of sonar: Navies use sonar to locate ships, submarines, and underwater mines. Fishing ships use sonar to detect schools of fish.
Emran Yusufov -- 2001