Question

What is SONAR? How does it work?

Answer 1

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.
In this method, to find the depth of an ocean, a strong ultrasonic wave is sent from the ship towards the bottom of the ocean. This ultrasonic wave is received back after it is reflected from the bottom of the sea. The time interval $t$ for travel of sound waves from the source to the receiver after reflection is noted.The distance travelled by the ultrasound ray is given by the equation: $2d=vt$, where $v$ is the velocity of sound. From this the depth d can be calculated.