|There is more information available on this subject at Radar on the English Wikipedia.|
Radar is a system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, vehicles, weather formations and terrain. The term RADAR was coined in the year 1941 as an acronym for Radio Detection And Ranging, persisting even into the 26th Century as an actual word.
A radar system has a transmitter that emits radio waves, that are reflected by the target and detected by a receiver, typically in the same location as the transmitter. Although the radio signal returned is usually very weak, radio signals can easily be amplified. This enables a radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar is used in many contexts, including meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, and by the UNSC Armed Forces.
Both the UNSC and Covenant utilize radar technologies, with the UNSC employing the X-ELF radar system aboard their Prowlers, and the Covenant using an unknown system aboard their own ships. The UNSC also once used the system to scour the skies for messages from extraterrestrial civilizations and uses Doppler radar systems in their weather stations.