The so-called sonar (sonar), the abbreviation of sound navigation and ranging, uses the physical characteristics of high propagation speed and low attenuation of sound waves in water to search, locate, identify and track targets in the water. The technical equipment is known as the underwater "clairvoyance" and "wind ear". During World War II, the British destroyer "Walker" used sonar to detect the position of the German submarine "U-99" and sank it to the bottom of the sea.
The world's first sonar was invented in 1971 by French physicist Langevin. Sonar works on the echo sounding method (similar to radar). Sonar is divided into passive sonar (or noise sonar) and active sonar according to its working mode. Today's sonar has both of the above. Take passive sonar as an example: when the target moves in the water or on the water surface, mechanical vibration and noise will be generated, which will be transmitted to the sonar transducer through the seawater medium. The transducer will convert the sound waves into electrical signals and then transmit them to the receiver. After amplification, it is transmitted to the display console for display and audiometric orientation. Passive sonar has good concealment and strong ability to identify targets, but it cannot detect stationary targets. Active sonar can solve this problem, but active sonar easily exposes itself and has a short detection range.
Initially, sonar was mainly used to detect enemy submarines. With the development of technology, sonar has developed to the fifth generation, that is, digital sonar, and its performance has been greatly improved. In addition to being used in the military for searching submarines, detecting mines, seabed warning, underwater navigation, underwater (torpedoes, mines, etc.) guidance and confrontation, it is also used for marine resource detection, research and development, such as detecting fish and shrimp swarms, detecting The depth of the ocean, submarine reefs, shipwrecks, oil pipelines, submarine cables and underwater obstacles, as well as submarine oil and gas, etc.