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Sonar

Sonar . By: David R icketts. Sonar.

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Sonar

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  1. Sonar By: David Ricketts

  2. Sonar • Sonar (originally an acronym for Sound Navigation And Ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.

  3. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. • Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and sodar(an upward looking in-air sonar) is used for atmospheric investigations.

  4. History • Although some animals (dolphins and bats) have used sound for communication and object detection for millions of years, use by humans in the water is initially recorded by Leonardo da Vinci in 1490: a tube inserted into the water was said to be used to detect vessels by placing an ear to the tube.

  5. Asdic • At the start of World War II, British ASDIC technology was transferred for free to the United States. Research on ASDIC and underwater sound was expanded in the UK and in the US. Many new types of military sound detection were developed.

  6. Sonar • During the 1930s American engineers developed their own underwater sound detection technology and important discoveries were made, such as thermo clines, that would help future development.

  7. Performance factors • The detection, classification and localisation performance of a sonar depends on the environment and the receiving equipment, as well as the transmitting equipment in an active sonar or the target radiated noise in a passive sonar.

  8. Sound propagation • Sonar operation is affected by variations in sound speed, particularly in the vertical plane. Sound travels more slowly in fresh water than in sea water, though the difference is small. The speed is determined by the water's bulk modulus and mass density.

  9. Scattering • When active sonar is used, scattering occurs from small objects in the sea as well as from the bottom and surface. This can be a major source of interference.

  10. Target characteristics • The sound reflection characteristics of the target of an active sonar, such as a submarine, are known as its target strength. A complication is that echoes are also obtained from other objects in the sea such as whales, wakes, schools of fish and rocks.

  11. Countermeasures • Active countermeasures may be launched by a submarine under attack to raise the noise level, provide a large false target, and obscure the signature of the submarine itself.

  12. Video on sonar • https://www.youtube.com/watch?v=-fAAxEIFeLU

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