RADAR : Radio Detection and Ranging
RADAR stands for Radio Detection and Ranging.
On January 7, 1952, after five years of testing and modifications to a radar system used by the Army and Navy in World War II, the Civil Aeronautics Administration inaugurated radar departure control procedures at its Washington National Airport. Six months later it began radar approach control procedures at the airport.
Radar was originally developed by the British during World War II, radar provided an important tool for U.S. armed forces in World War II. The term Radio Detection And Ranging equipment, coined as RADAR by the U.S. Navy in 1940 and it allowed the military to adapt and use a new landing aid called Ground Control Approach (GCA).
The military selected company Gilfillan Brothers, Inc. in Los Angeles, CA, to develop the system in 1942. The following year, U.S Air Force air traffic controllers began routinely using GCA equipment to help military pilots land safely in poor visibility. The system was not designed for en route air traffic control.
How Radar Works?
A radar system has a transmitter that emits radio waves known as radar signals in predetermined directions. When these signals contact an object, they are usually reflected or scattered in many directions, although some of them will be absorbed and penetrate into the target. Radar signals are reflected especially well by materials of considerable electrical conductivity such as most metals, seawater, and wet ground. This makes the use of radar altimeters possible in certain cases. The radar signals that are reflected back towards the radar receiver are the desirable ones that make radar detection work. If the object is moving either toward or away from the transmitter, there will be a slight change in the frequency of the radio waves due to the Doppler effect.
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Radar receivers are usually, but not always, in the same location as the transmitter. The reflected radar signals captured by the receiving antenna are usually very weak. They can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals.
The weak absorption of radio waves by the medium through which they pass is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Weather phenomena, such as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided when designing radars, except when their detection is intended.
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