radar

Radar is an object-detection system that uses electromagnetic waves - specifically radio waves - to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, mountain ranges, radio and TV towers, guided missiles, motor vehicles, weather formations, and terrain. The radar dish, or antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.

The term RADAR was coined in 1940 by electronics engineers working for the U.S. Navy as an acronym for RAdio Detection And Ranging. The term radar has since entered the English language as the common noun, radar, losing all of the capitalization. Radar was originally called by the term RDF (Range and Direction Finding) in the United Kingdom, using the same acronym as the one for Radio Direction Finding in order to conceal its ranging capability from unwanted listeners, such as foreign secret agents.. Also, in German, the word is Radar - simply because in German, all nouns are capitalized. In English, the word radar is also used as an adjective, as in radar antenna.

The uses of radar include air traffic control, radar astronomy, air-defense systems, antimissile systems; nautical radars to locate landmarks and other ships; aircraft anticollision systems, ocean-surveillance systems, outer-space surveillance and rendezvous systems; meteorological precipitations, radar altimeters, earth-skimming flight-control systems, guided-missile target-locating systems, and ground-penetrating radars.

Other systems similar to radar have been used in other parts of the electromagnetic spectrum, such as "lidar", which uses visible light from lasers, rather than radio waves.