Sonar
Also called: Sound Navigation and Ranging · Topic: Remote Sensing, GIS and GNSS · NCERT: Beyond NCERT
Meaning
Sonar (Sound Navigation and Ranging) uses sound to find and locate objects underwater. An active sonar sends out a sound pulse, called a "ping". The ping hits an object or the sea floor and bounces back as an echo. The time the echo takes to return gives the distance, because sound travels at a known speed in water (about 1,500 metres per second). Sonar is needed under the sea because radio waves and light fade quickly in water, so radar and cameras cannot see far there. It is the main sensor of a submerged submarine. It is also used to map the depth and shape of the ocean floor. This is called echo sounding.
Example
A conventional (diesel-electric) submarine of the Indian Navy, travelling underwater in the Bay of Bengal, uses sonar to detect ships, other submarines and the sea bed. It uses its periscope and radar only when it is at or near the surface. Survey ships use echo sounders, a simple form of sonar, to chart sea depths off India's coasts so that ships can avoid shallow banks.
Don't confuse with
- Radar: sends out microwave (radio) pulses, not sound. It works through air, cloud and darkness, from aircraft and satellites, but not underwater.
- LiDAR: fires laser (light) pulses, usually from aircraft, to measure land heights. Sonar uses sound waves in water.