Sonar

Sonar (short for Sound Navigation And Ranging) is a technology that uses acoustical waves to detect the location of objects underwater. Simple sonar devices are comprised of a transducer, which emits a sound pulse out from a watercraft. The amount of time it takes the sound wave to return to the transducer is then measured. Distance to an object can then be calculated using this time difference and the speed of sound in the water (approximately 1500 meters per second). More advanced sonar systems are able to calculate additional direction and range information.

Sonar technology is widely associated with submarines, underwater vessels that rely on sonar in order to detect objects and other ships in order to navigate through the water safely. Sonar is also used to develop nautical charts, as well as locate underwater hazards, search for and map objects on the seafloor such as shipwrecks, as well as map the seafloor itself.

A video from the U.S. National Oceanic and Atmospheric Administration (NOAA) showing how sonar is used to map the ocean floor.

Sonar can be classified into two categories: active and passive. Active sonar, described above, is when a transducer emits a sound pulse towards an object and measures the amount of time the sound waves take to bounce back (echo). Distance is then calculated using this time distance and the rate sound travels underwater. Passive sonar differs in that it does not emit its own signal. Instead, passive sonar only detects sound waves coming towards the receiver. Passive sonar cannot be used to measure the range of an object unless it is used in conjunction with other passive sonar devices, which could be used to triangulate the source of a sound.

One of the earliest iterations of sonar technology dates back to 1906, when naval architect Lewis Nixon created a sonar-like device designed to detect icebergs underwater. This detection system became much more important after the Titanic disaster in 1912. With the onset of World War I and the introduction of in submarine warfare in 1914, research into sonar technology again became a priority. In 1915, French physicist Paul Langevin worked with Russian engineer Constantin Chilowski in order to create the first active sonar device for submarine detection. This technology continued to improve, and it became especially useful in World War II in conjunction with increased naval submarine use.

Research into sonar technology and its uses continues to this day, including the following programs: