Types and uses of radar


Types and uses of radar

Radar has many different types and applications:
* "Search radars" scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. The waves are usually less than a meter long. Ships and planes are metal, and reflect radio waves. The radar measures the distance to the reflector by measuring the time from emission of a pulse to reception, and dividing by the speed of light. To be accepted, the received pulse has to lie within a period of time called the "range gate". The radar determines the direction because the short radio waves behave like a search light when emitted from the reflector of the radar set's antenna.

* "Targeting radars" use the same principle but scan a much smaller area far more often, usually several times a second or more, where a search radar might scan a few times per minute. Some targeting radars have a range gate that can track a target, to eliminate clutter and electronic counter-measures.

* "Radar proximity fuzes" are attached to anti-aircraft artillery shells or other explosive devices, and detonate the device when it approaches a large object. They use a small rapidly pulsing omnidirectional radar, usually with a powerful battery that has a long storage life, and a very short operational life. The fuzes used in anti-aircraft artillery have to be mechanically designed to accept fifty thousand"g", yet still be cheap enough to throw away.

* "Weather radars" can resemble search radars. This radar uses radio waves along with horizontal, dual (horizontal and vertical), or circular polarization. The frequency selection of weather radar is a performance compromise between precipitation reflectivity and attenuation due to atmospheric water vapor. Some weather radars uses doppler shift to measure wind speeds.

* "Marine radars" are used by ships for collision avoidance and navigation purposes. The frequency band of radar used on most ships is x-band (9 GHz/3 cm), but s-band (3 GHz/10 cm) radar is also installed on most ocean going ships to provide better detection of ships in rough sea and heavy rain condition. Vessel Traffic Centre also use marine radars (x or s band) for tracking ARPA and provides collision avoidance or traffic regulation of ships in the survallence area.

*"Navigational radars" resemble search radar, but use very short waves that reflect from earth and stone. They are common on commercial ships and long-distance commercial aircraft.

* "General purpose radars" are increasingly being substituted for pure navigational radars. These generally use navigational radar frequencies, but modulate the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms, as well as land and vehicles. Some can superimpose sonar and map data from GPS position.

* "Radar altimeters" measure an aircraft's true height above ground.
* Air traffic control uses Primary and Secondary Radars.
**Primary radar is a "classical" radar which reflects all kind of echoes, including aircraft and clouds.

**Secondary radar emits pulses and listens for special answer of digital data emitted by an Aircraft Transponder as an answer. Transponders emit different kind of data like a 4 octal ID (mode A), the onboard calculated altitude (mode C) or the Callsign (not the flight number) (mode S). Military use transponders to establish the nationality and intention of an aircraft, so that air defenses can identify possibly hostile radar returns. This military system is called IFF (Identification Friend or Foe).

*"Mapping radars" are used to scan a large region for remote sensing and geography applications. They generally use synthetic aperture radar, which limits them to relatively static targets, normally terrain.

* [http://www.wearcam.org/ece431/labs/lab3/lab3.htm Wearable radar] and miniature radar systems are used as electric seeing aids for the visually impaired, as well as early warning collision detection and situational awareness.


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