SONAR stands for Sound Navigation And Ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects. Sonar consists of a transmitter and a detector and is installed at the bottom of boats and ships.
The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound.
Let the time interval between transmission and reception of ultrasound signal be ‘t’ and
the speed of sound through sea water be 2d = v × t. This method is called echo-ranging. Sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarine, icebergs etc.
A ship sends out ultrasound that returns from the seabed and is detected after 3.42 s. If the speed of ultrasound through sea water is 1531m s-1, what is the distance of the seabed from the ship?
Time between transmission and detection, t = 3.42 s.
Speed of ultrasound in sea water, v = 1531m s–1
Distance travelled by the ultrasound = 2 × depth of the sea
We know, distance = speed × time
2d = speed of ultrasound × time
2d = 1531×3.42
∴d = 5236/2 m
d = 2618 m
Thus, the distance of the seabed from the ship is 2618 m or 2.618 km