The sinking of the British liner Titanic in 1912, after hitting an iceberg, spurred scientists to find a way to detect obstacles underwater. British and American forces used a form of sound detection against submarines in World War I. Scientist Paul Langevin created the sonar that uses the echo of emitted sounds.
Today, echo pickup is used in navigation to determine water depth, to locate fish shoals, and in marine research and ocean floor mapping. The sound pulses are emitted through the water and their echoes are reflected back to the boat by any obstacle 10 km away. The received signals are displayed on a video screen.
The sound travels in the water at about 1,500 m per second. The distance to the obstacle is calculated by the time it takes for the echo to return, and the Doppler effect of the sound waves shows if the object is moving.
.
