What is SONAR ? How is it used to detect an underwater object and measure its distance ?

Explanation

A SONAR is a device which measures the distance, direction and speed of objects lying under water using ultrasonic waves.
A sonar, which is installed in a ship or a boat, consists of (i) a transmitter and (ii) a receiver. The ultrasonic waves produced by the transmitter travel through water. After getting reflected by the object on the sea bed, these waves are picked up by the receiver. The receiver converts the reflected ultrasonic waves into electrical signals which are properly recorded.
Let `t =` time interval between the transmission and reception of the reflected ultrasound waves,
`v=` speed of sound through sea water,
`d =` distance of the object that reflected the ultrasound.
Clearly, total distance travelled by the ultrasound `=2d`
As distance `=` speed `xx` time
`2d = vt`
or `d = (v t)/( 2)`
The above method of finding the distance of an object is called echo-ranging as it is based on echo principle. The SON AR technique is used to determine depth of the sea. When used for this purpose, it is called a fathometer as it directly measures the depth of the sea.