How does Sonar Work?

Sonar is a system used to locate things underwater, to measure the depth of sea underneath a vessel and to locate a shoal offish. It was invented in 1915 by Professor Langevin in France to detect icebergs following the sinking of Titanic in 1912. Sonar takes its name from sound navigation and ranging. It works like a radar except that sonar uses sound signals instead of radio signals. Sonar works by transmitting short bursts of sound and picking up reflections or echoes bouncing back from the obstacles in their path. The distance of the obstacle is calculated from the time interval between the transmitted and reflected pulses. The frequency of sound used is so high that it is beyond the highest frequency that can be heard by the human ear. The sonar screens use sound waves to build up pictures.