Radio Detection And Ranging, system or technique for detecting
the position, Motion, and nature of a remote object by means of Radio Waves refle
cted from its surface. Radar systems transmit pulses of Electromagnetic Waves (usually Microwave(s) ) by means of directional Antennas; some of th
e pulses are reflected (see Reflection) by objects in the path of the beam. Reflections are received by the radar
unit, processed electronically, and converted into images on a Cathode-Ray Tube. The distance of the object from the radar source is determined by measuring
the Time required for the radar signal to reach the target and return. The direction
of the object with respect to the radar unit is determined from the direction in
which the pulses were transmitted. In most units, the beam of pulses is
continuously rotated at a constant speed, or it is scanned (swung back and forth)
over a sector at a constant rate. In doppler radar, the velocity of the object is
determined using the Doppler Effect: if the object is approaching the radar unit, the Frequency of the returned signal is greater than the frequency of the transmitted
signal; if the object is receding, the returned frequency is less; and if the object
is not moving relative to the radar unit, the frequency of the returned signal
is the same as the frequency of the transmitted signal. Doppler radar can
measure Wind rotation inside a thunderstorm and is used to identify possible Tornados.