The sonar device measures the _________ it takes the reflected sound waves to return to the device.

Sonar is a commonly used device to measure the depth of a water body, such as river, sea, pond, etc. The term SONAR stands for sound navigation and ranging. Sonar uses sound waves and determines the time it takes an emitted sound wave to return back to the device. Since we know the velocity of sound in water, we can use the measured time interval to determine the depth of the water body. Using this depth at various locations, we can map the surface of the river or ocean. Sonar can also be used to detect the presence of large objects in the water bodies and is commonly used by navy to determine the presence of submarines. Sonar can be classified as either active or passive, depending upon whether it emits the sound waves (active sonar) or not. 

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