What is SONAR

Sonar is a device that uses sound to locate position of
objects submerged in deep waters. More sophisticated varieties of sonars can also
generate pictures of these objects and determine speed of moving objects. The word sonar
is formed by combination of two terms used in navigation - sound  navigation and
ranging.

As compared to radars sonars are better suited for
many underwater applications as sound travels faster and more efficiently in water,
whereas radio waves face greater distortion in water.  Some sonar devices are designed
to operate in air also. For example, some varieties of burglar alarms use airborne
ultrasound waves to detect movement.

There are two types of
sonars - active and passive sonars. Active sonar send out sound waves which travel
through the water until they strike an object, and are reflected by them in various
directions.  Some of the reflected waves return to the sonar, where they strike a
receiver, which converts the sound back into electrical signals. These signals are then
analyse to produce the required information. Passive sonars use the sound given off by
other objects. These type of sonars are not very effective in ascertaining the distances
of the object under study.

It is interesting to note that
dolphins and bats use natural sonar techniques called ecolocation to locate food, avoid
obstacles and to communicate.