Sonar

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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. 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. !onar may be used as a
means ofacoustic location and of measurement of the echo characteristics of "targets" in the water.
"coustic location in air was used before the introduction of radar. !onar may also be used in air for
robot navigation, and !#$"% (an upward loo&ing in'air sonar) is used for atmospheric
investigations. The term sonar is also used for the equipment used to generate and receive the
sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to e(tremely
high (ultrasonic). The study of underwater sound is &nown as underwater
acoustics or hydroacoustics.
History
"lthough some animals (dolphins and bats) have used sound for communication and object
detection for millions of years, use by humans in the water is initially recorded by)eonardo da
*inci in +,-.: a tube inserted into the water was said to be used to detect vessels by placing an ear
to the tube
The use of sound to /echo locate/ underwater in the same way as bats use sound for aerial
navigation seems to have been prompted by the Titanic disaster of +-+0. 1erman
physicist "le(ander 2ehm obtained a patent for an echo sounder in +-+3. "mericans began to use
the term SONAR for their systems, coined as the equivalent of %"$"%.
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.
Countermeasures
Active (powered) countermeasures may be launched by a submarine under attac& to raise the noise
level, provide a large false target, and obscure the signature of the submarine itself.
Passive (i.e., non'powered) countermeasures include:
• 4ounting noise'generating devices on isolating devices.
• !ound'absorbent coatings on the hulls of submarines, for e(ample anechoic tiles.
"ctive sonar creates a pulse of sound, often called a "ping", and then listens for reflections (echo) of
the pulse. To measure the distance to an object, the time from transmission of a pulse to reception is
measured and converted into a range by &nowing the speed of sound.
5hen active sonar is used to measure the distance from the transducer to the bottom, it is &nown
as echo sounding.
6assive sonar listens without transmitting. 7t is often employed in military settings, although it is also
used in science applications, e.g., detecting fish for presence8absence studies in various aquatic
environments.
Ultrasound is an oscillating sound pressure wave with a frequency greater than the upper limit of
the human hearing range. Ultrasonics is the application of ultrasound. 9ltrasound can be used
for medical imaging, detection, measurement and cleaning. "t higher power levels, ultrasonics is
useful for changing the chemical properties of substances.
The first technological application of ultrasound was an attempt to detect submarines by 6aul
)angevin in +-+:. Thepie;oelectric effect, discovered by <acques and 6ierre =urie in +>>., was
useful in transducers to generate and detect ultrasonic waves in air and water.
?0@
Acholocation in bats
was discovered by )a;;aro !pallan;ani in +:-,, when he demonstrated that bats hunted and
navigated by inaudible sound and not vision.
An ultrasound scan, sometimes called a sonogram, is a
procedure that uses high frequency sound waves to create an
image of part of the inside of the body, such as the heart
"s sound waves are used rather than radiation, the procedure is
safe. 9ltrasound scans are commonly used during pregnancy to
produce images of the baby in the womb.
9ltrasound scans can also be used to:
• detect heart problems
• e(amine other parts of the body such as the liver, &idneys and abdomen
• help guide a surgeon performing some types ofbiopsy

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