SONAR is an acronym for Sound Navigation and ranging. It is an apparatus or device that uses the principle of reflection of ultrasound waves or detect the presence of underwater objects and determine their distance (i.e., range) as well as speed and direction of motion (i.e., navigation). Some common uses of SONAR are -

    1. Detecting enemy submarines

    2. Determining sea depth

    3. Finding fish

    4. Finding ship wrecks

    5. Locating underwater pipelines, icebergs, valley and hills

    6. Mapping ocean floor

    7. Ship to ship communication



    Working Principle of SONAR

    SONAR consists of an ultrasound transmitter (sender) and a detector (or receiver). Usually, it is fitted at the bottom of a ship or boat. The transmitter produces and transmits high frequency ultrasound waves into water in search of an object. When these waves strike an object, they are reflected back. The detector collects the reflected waves. (The reflected waves are actually the echoes of the transmitted waves.) The reflected ultrasound waves are converted into electrical signals by appropriate devices. The electrical signals are then correctly interpreted to provide the required information regarding the distance, speed and direction of motion of the object.

    Let the time interval between transmission and reception of ultrasound signal is t. Speed of sound through sea water is v, total distance travelled by waves = 2d. Then, 2d = v × t.  


    This equation can be used to find the distance of the underwater objects. This method of measuring distances of underwater objects is called echo-ranging, as it is based on recording an echo. This technique can be used to determine the depth of seabed, underwater hills, valleys, submarines, icebergs, sunken ships, large fish colonies, etc.