Skip to main content
Select Source:

RADAR

RADAR

LARRY GILMAN

RADARan acronym for RAdio Detection And Ranging is the use of electromagnetic waves at sub-optical frequencies (i.e., less than about 1012 Hz) to sense objects at a distance. Hundreds of different RADAR systems have been designed for various purposes, military and other. RADAR systems are essential to the navigation and tracking of craft at sea and in the air, weather prediction, and scientific research of many kinds.

Principles. In basic RADAR, radio waves are transmitted from an antenna. These outgoing waves eventually bounce off some distant object and return an echo to the sender, where they are received, amplified, and processed electronically to yield an image showing the object's location. The waves sent out may be either short oscillatory bursts (pulses) or continuous sinusoidal waves. If a RADAR transmits pulses it is termed a pulse RADAR, whereas if it transmits a continuous sinusoidal wave it is termed a continuous-wave RADAR.

On closer examination, the RADAR process is seen to be more complex. For example, reflection of an echo by the object one wishes to sense is anything but straightforward. Upon leaving a transmitting antenna, a radio wave propagates in a widening beam at the speed of light (> 186,000 miles per hour [3 × 108 m/sec]); if it encounters an obstacle (i.e., a medium whose characteristic impedance differs from that of air and vacuum [> 377 ), it splits into two parts. One part passes into the obstacle and is (generally) absorbed, and the other is reflected. Where the reflected wave goes depends on the shape of the obstacle. Roundish or irregular obstacles tend to scatter energy through a wide angle, while flat or facet-like surfaces tend to send it off in a single direction, just as a flat mirror reflects light. If any part of the outgoing wave is reflected at 180° (which is not guaranteed) it will return to the transmitter. This returned or backscattered signal is usually detected by the same antenna that sent the outgoing pulse; this antenna alternates rapidly between transmitting pulses and listening for echoes, thus building a realtime picture of the reflecting targets in range of its beam. The energy the echoes receive is a small fraction of that in the pulses transmitted, so the strength of the transmitted pulse and the sensitivity of the receiver determines a RADAR's range. By systematically sweeping the direction in which its antenna is pointed, a RADAR system can scan a much larger volume of space than its beam can interrogate at any one moment; this is why many RADAR antennas, on ships or atop air-traffic control towers, are seen to rotate while in operation.

Radio waves are not the only form of energy that can be used to derive echoes from distant targets. Sound waves may also be used. Indeed, because radio waves are rapidly absorbed in water, sonar (SOund Navigation and Ranging) is essential to underwater operations of all sorts, including sea-floor mapping and anti-submarine warfare.

Applications. Since World War II RADAR has been deployed in many forms and has found a wide application in scientific, commercial, and military operations. RADAR signals have been bounced off targets ranging in size from dust specks to other planets. RADAR is essential to rocketry and early-warning detection of missiles, air traffic control, navigation at sea, automatic control of weapons such as antiaircraft guns, aircraft detection and tracking, mapping of the ground from the air, weather prediction, intruder detection, and numerous other tasks. Few craft, military or civilian, put to sea or take to the air without carrying some form of RADAR.

In recent decades, development of the basic RADAR principlesend pulse, listen for echohas proceeded along a number of interesting paths. By exploiting the Doppler effect, which causes frequency shifts in echoes reflected from moving objects, modern RADARs can tell not only where an object is but what direction it is moving in and how quickly. The Doppler effect also allows for the precision mapping of landscapes from moving aircraft through the synthetic-aperture technique. Synthetic-aperture systems exploit the fact that stationary objects being swept by a RADAR beam projected from a moving source have, depending on their location, slightly different absolute velocities with respect to that source. By detecting these velocity differences using the Doppler effect, synthetic aperture type RADAR greatly permits the generation of high-resolution ground maps from small, airborne RADARs.

In many modern RADAR systems the need for a mechanically moving antenna has been obviated by phased arrays. A phased array consists of a large number of small, computer-controlled antennas termed elements. These elements, of which there are usually thousands, are crowded together to form a flat surface. In transmit mode, the elements are all instructed to emit a RADAR pulse at approximately the same time; the thousands of outbound waves produced by the elements merge into a single powerful wave as they spread outward. By timing, or phasing, the elements in the array so that, for example, elements along the left-hand edge of the array fire first while those farther to the right fire progressively later, the composite wave formed by the merging of the elements' lesser outputs can be steered in any desired direction within a wide cone (in this example, to the right). Beam steering can be accomplished by such a system millions of times more rapidly than would be possible with mechanical methods. Phased-array systems are used for a number of applications; including the 71.5-foot (21.8-m) tall AN/FPS-115 PAVE PAWS Early Warning RADAR Array Antennas, which provide early warning of ballistic-missile attack; shipboard systems such as the AN/SPY-1D, which is about 15 feet (3 m) across and is mounted flush with the upper hull of some warships; the Hughes AN/TPQ-37 Firefinder, a trailer-mounted system designed for tracking incoming artillery and missiles and calculating their point of origin; and many other real-world systems.

RADAR is a powerful weapon of war, but has its weaknesses. For example, numerous missiles have been developed to home in on the radio pulses emitted by RADARs, making it very dangerous to turn on a RADAR in a modern battlefield situation. Further, jamming and spoofing ("electronic warfare") have evolved rapidly alongside RADAR itself. For example, an aircraft that finds itself interrogated by a RADAR pulse can emit blasts of noise or false echoes, or request that a drone or other unit emit them, in order to confuse enemy RADAR. Finally, aircraft have been built that are "low observable," that is, which scatter very little energy back toward any RADAR that illuminates them. Low-observable or "stealth" aircraft are built of radio-absorbent materials and shaped to present little or no surface area perpendicular to RADAR pulses approaching from most angles (except directly above and directly below, the two least likely places for an enemy RADAR to be at any given moment). What RADAR they do reflect is deflected at low angles rather than returned to the RADAR transmitter. The U.S. B-2 bomber and F-117A and F-22 fighters are working examples of low-observable aircraft.

FURTHER READING:

BOOKS:

Edde, Byron. RADAR: Principles, Technology, Applications. Englewood Cliffs, NJ: PTR Hall, 1993.

Skolnik, Merrill I. Introduction to RADAR Systems. New York: McGraw Hills, 2001.

SEE ALSO

Stealth Technology
RADAR, Synthetic Aperture

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"RADAR." Encyclopedia of Espionage, Intelligence, and Security. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"RADAR." Encyclopedia of Espionage, Intelligence, and Security. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/radar

"RADAR." Encyclopedia of Espionage, Intelligence, and Security. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/radar

RADAR

RADAR, an acronym for RAdio Detection And Ranging, is based on German scientist Heinrich Hertz's 1880s discovery that a beam of radio energy that strikes an object of sufficient density will be reflected by it. If that reflected energy is then captured by a receiver at the beam's origin it can be analyzed. Another German scientist, Christian Hulsmeyer, patented the first radio echo device in 1904. Because radio energy travels at a constant speed (the speed of light) the length of time between sending and receiving the energy can thus be used to calculate the object's distance. The direction from which the energy is received can be used to determine the object's bearing. Combining distance and bearing indicates the object's location on/above the surface of the Earth. Modern radars belong to one of two general types. Pulse radars emit a short, intense burst of radio energy, while continuous‐wave radars emit a steady signal. The latter, often called Doppler radar, cannot track the range to the object but instead measures the Doppler shift caused by the object's movement, from which the direction and speed of its movement can be determined. There are several other specific types of radars, such as Synthetic Aperture Radar, which electronically focus or shape the radar beam.

The Italian Guglielmo Marconi first demonstrated radio reflection for detection in the 1920s. In the United States, Gregory Breit and Merle A. Tuve discovered the principle of pulse ranging in 1925. Research and development was underway simultaneously in Germany, Great Britain, and the United States by the early 1930s. The Germans initially had better equipment aboard warships that began radar‐aided commerce raiding in September 1939. In 1937 the British began deploying the Chain Home early warning network along the Channel coast, which would provide the decisive advantage in the Battle of Britain. Early World War II radars used radio pulses of low frequency and long (a meter or more) wavelength, but these required large antennas, suitable only for large ships or ground stations and were imprecise compared to the next generation radars. With the invention in Great Britain of the cavity magnetron in 1940, however, much smaller sets employing centimeter wavelengths capable of much greater precision were possible. In 1940 Henry Tizard led a mission to the United States that successfully enlisted American industrial aid, and the Germans fell behind, never to regain parity. In the Pacific, the Japanese never even came close to it, and most Japanese radar systems were based on early ones captured from the British and Americans in 1942.

At sea, Allied naval radar was key in the defeat of the U‐boat threat in 1943, and radar‐directed naval gunfire was decisive in several sea battles, including the Battle of Leyte Gulf in October 1944, in which US battleships in the Surigao Straits using radar‐directed gunfire at night destroyed a Japanese fleet. In the air, the radar struggle between countermeasure and counter‐countermeasure was dynamic, deadly, and decisive. In July 1943 the Royal Air Force first used “window” (American term: “chaff”), small strips of reflective tinfoil, to negate German air defenses of Hamburg (Operation “Gomorrah”) in a raid that killed approximately 40,000 inhabitants. American bombers equipped with radar jamming transmitters (called “Carpet”) blocked German “Wurzburg” anti‐aircraft gun‐ laying radars and assisted in a deceptive spoof on the night of the Normandy landings. Offensively, American and British aircraft carried increasingly sophisticated navigational radars, such as the H2S and H2X (“Mickey”) sets that portrayed ground features with greater and greater detail and enabled bombing at night or through cloud cover. Night fighters equipped with small radar sets such as the German “Lichtenstein” hunted enemy aircraft in the darkness and located them entirely by radar. Specialized aircraft (“ferrets”) gathered radar intelligence while electronic warfare operators (“ravens”) waged an invisible but critical war in what was then called “the ether,” and might today be called “cyberspace.”

During the Cold War both the U.S. and Russians erected radar networks such as the Distant Early Warning or “DEW” line across Canada to warn of enemy aircraft. Strategic Air Command (SAC) warplans from the 1950s through the 1980s depended on radar to accurately navigate to and identify targets, and electronic countermeasures (ECM) such as radar jamming and chaff were the key to negating enemy defenses. Intercontinental ballistic missiles forced both sides in the 1960s to develop even more sophisticated radar nets such as the Ballistic Missile Early Warning System (BMEWS) to warn of missile attack. Perhaps the ultimate were radars devised to support anti‐ missile defenses, capable of not only detecting enemy missiles in space but also of tracking them for interception and destruction by defensive missiles. Radars belonging to the Space Detection and Tracking System (SPADATS) keep constant track of the thousands of objects orbiting the earth.

The air war over Vietnam was dominated by radar controlled air defenses, as North Vietnam successfully employed Russian radar‐guided surface‐to‐air missiles (SAMs) against American air operations. American countermeasures included not only traditional ECM, but also direct attacks on radar control systems. This technique, called “Wild Weasel”, had been tried in WW II, but not until the 1960s were detection and homing systems sufficiently advanced to be successful. Anti‐radar electronic warfare EW) was so important by the Persian Gulf War of 1991 that virtually no Coalition aerial attacks were mounted without EW support. Since the 1940s, designers have sought aircraft undetectable by enemy radars. This effort came to fruition with the F‐117 “Stealth Fighter” and B‐2 “Stealth Bomber”, both of which used Low Observable technology to make them almost invisible to enemy radars.

Modern military radars have become increasingly sophisticated, and those mounted in surveillance aircraft such as the Airborne Warning and Control System (“AWACS”) or Joint Surveillance and Tracking Radar System (“JSTARS”) provide virtually a three‐dimensional portrayal of a battlespace the size of a small country. Radar has also had an enormous effect in the civilian world. From radar astronomy, to traffic control, to weather and storm warning, to air and maritime navigation, radar has become an indispensable facet of modern life.

Bibliography

Alfred Price , Instruments of Darkness (1977).
Alfred Price , The History of US Electronic Warfare, Volumes I and II (1984, 1989).
Henry E. Guerlac , Radar in World War II (1987).
David Pritchard , The Radar War (1989).
Robert Buderi , The Invention That Changed the World (1996).
Alan Beyerchen , From Radio to Radar: Interwar Military Adaptation to Technological Change in Germany, the UK, and the US, in Alan R. Millet and Williamson Murray, editors, Military Innovation in the Interwar Period, (1996).

Daniel T. Kuehl

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"RADAR." The Oxford Companion to American Military History. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"RADAR." The Oxford Companion to American Military History. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/radar

"RADAR." The Oxford Companion to American Military History. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/radar

Radar

RADAR

RADAR, an acronym for "radio detection and ranging," is a method of locating distant targets by sending bursts of electromagnetic radiation and measuring their reflections. In the most common method, ultrashort radio waves are beamed toward the target by a scanning antenna. The resulting echoes are then displayed on a cathode-ray tube by means of a scanning signal synchronized with the antenna, so that the echo from each target appears as an illuminated dot, in the appropriate direction and at a proportional distance, on a map of the entire area being scanned. In other versions, continuous waves are used, and, in some, only moving targets are revealed (for example, in police sets used to detect speeding vehicles).

The science behind radar dates to the 1920s, when radio operators noticed perturbations caused by obstacles moving in a radio field. Such effects were familiar to both amateur and professional radio enthusiasts in many countries and were at first freely discussed in engineering journals. As the military significance of these observations dawned on researchers in government laboratories in the 1930s, such references grew rarer. Two American reports, in particular, helped shape the nascent science of radio detection: a 1933 report (by C. R. Englund and others in the Proceedings of the Institute of Radio Engineers) describing a systematic investigation of the interferences caused by overflying aircraft and a 1936 report (by C. W. Rice in the General Electric Review) on the uses of ultrahigh-frequency


equipment, among which was listed "radio-echo location for navigation."

The first innovations came from the commercial sector. Radio altimeters were developed to gauge the altitude of planes; experimental equipment intended to prevent collisions was installed on the French Line's giant ship Normandie, producing considerable publicity but only moderate success. Scientists, as well, found applications for these early forms of radar technology. They used radio detection to locate storms, measure the height of the ionosphere, and survey rugged terrain. Essential technologies evolved from these experiments, such as ultrahighfrequency (microwave) tubes, circuits, and antennas; cathode-ray (picture) display tubes; and wide-band receivers capable of amplifying and resolving extremely short pulses of one-millionth of one second (microsecond) or less.

As World War II approached, military laboratories in several countries rushed to develop systems capable of locating unseen enemy ships and aircraft. Such a capability, military planners knew, would provide enormous tactical advantages on sea and in the air. Six countries led the race—the United States, Great Britain, France, Germany, Italy, and Japan—but there were doubtless others, including Canada, the Netherlands, and the Soviet Union. Great Britain made the swiftest progress before the outbreak of the war. A team assembled by the engineer Robert Watson-Watt devised a system of radar stations and backup information-processing centers. This complex was partly in place when war broke out in September 1939 and was rapidly extended to cover most of the eastern and southern coasts of England. By the time of the air Battle of Britain a year later, the system was fully operational. The British radar system is credited with swinging the balance in the defenders' favor by enabling them to optimize their dwindling air reserves.

American military developments had started even earlier, in the early 1930s, and were carried on at fairly low priority at the Naval Research Laboratory under R. M. Page and at the army's Signal Corps laboratories under W. D. Hershberger. By the time the United States entered the war, radar had been installed on several capital warships and in a number of critical shore installations. Indeed, a radar post in the hills above Pearl Harbor spotted the Japanese attack in December 1941, but the backup system was not in place and the warning did not reach the main forces in time. American forces in the Pacific quickly corrected this situation, and radar played a significant role six months later in the pivotal victory over a Japanese naval force at Midway Island.

British researchers had not been idle in the meantime. Great Britain made a great step forward with the invention of a high-power magnetron, a vacuum tube that, by enabling the use of even shorter centimetric wavelengths, improved resolution and reduced the size of the equipment. Even before the attack on Pearl Harbor, a British delegation led by Sir Henry Tizard had brought a number of devices, including the centimetric magnetron, to the United States in an effort to enroll U.S. industry in the war effort, since British industry was already strained to full capacity. The resulting agreement was not entirely one-sided, since it placed some American developments at the Allies' disposal: for instance, the transmit-receive (TR) tube, a switching device that made it possible for a single antenna to be used alternately for radar transmission and reception. From then on until the end of the war, British and U.S. radar developments were joined, and the resulting equipment was largely interchangeable between the forces of the two nations.

The principal U.S. radar research laboratories were the Radiation Laboratory at the Massachusetts Institute of Technology (MIT), directed by Lee Du Bridge, where major contributions to the development of centimetric radar (including sophisticated airborne equipment) were made; and the smaller Radio Research Laboratory at Harvard University, directed by F. E. Terman, which specialized in electronic countermeasures (i.e., methods of rendering enemy's radar ineffective and overcoming its countermeasures). The MIT group produced an elaborate and detailed twenty-eight-volume series of books during the late 1940s that established a solid foundation for worldwide radar developments for several decades.

Wartime industrial advances gave U.S. manufacturers a head start over foreign competitors, notably in the defeated nations, where war-related industries remained shut down for several years. Postwar developments were enhanced by commercial demand—there was soon scarcely an airport or harbor any where that was not equipped with radar—and by the exigencies of the space age, including astrophysics. Many of the basic inventions of World War II remained fundamental to new developments, but additional refinements were introduced by researchers in many countries. Among them, the contributions of Americans were perhaps the most numerous and ensured that American-made radar equipment could compete in world markets despite high production costs.

BIBLIOGRAPHY

Buderi, Robert. The Invention that Changed the World. New York: Simon and Schuster, 1996.

Burns, Russell, ed. Radar Development to 1945. London: Institution of Electrical Engineers, 1988.

Fisher, David E. A Race on the Edge of Time. New York: McGrawHill, 1988.

Page, Robert M. The Origin of Radar. Garden City, N.Y.: Anchor Books, 1962.

CharlesSiisskind/a. r.

See alsoAir Defense ; Aircraft Industry ; Signal Corps, U.S. Army ; Weather Service, National .

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Radar." Dictionary of American History. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"Radar." Dictionary of American History. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/history/dictionaries-thesauruses-pictures-and-press-releases/radar

"Radar." Dictionary of American History. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/history/dictionaries-thesauruses-pictures-and-press-releases/radar

radar

radar, system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, the principle of radar is not confined to any particular frequency range. There are some radar units that operate on frequencies well below 100 megahertz (megacycles) and others that operate in the infrared range and above. The term radar, an acronym for radio detection and ranging, is also used to denote the apparatus for implementing the technique.

Principles of Radar

Radar involves the transmission of pulses of electromagnetic waves by means of a directional antenna; some of the pulses are reflected by objects that intercept them. The reflections are picked up by a receiver, processed electronically, and converted into visible form by means of a cathode-ray tube. The range of the object is determined by measuring the time it takes for the radar signal to reach the object and return. The object's location with respect to the radar unit is determined from the direction in which the pulse was received. In most radar units the beam of pulses is continuously rotated at a constant speed, or it is scanned (swung back and forth) over a sector, also at a constant rate. The velocity of the object is measured by applying the Doppler principle: 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 from the radar unit, the returned frequency is less; and if the object is not moving relative to the radar unit, the return signal will have the same frequency as the transmitted signal.

Applications of Radar

The information secured by radar includes the position and velocity of the object with respect to the radar unit. In some advanced systems the shape of the object may also be determined. Commercial airliners are equipped with radar devices that warn of obstacles in or approaching their path and give accurate altitude readings. Planes can land in fog at airports equipped with radar-assisted ground-controlled approach (GCA) systems, in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot. A ground-based radar system for guiding and landing aircraft by remote control was developed in 1960.

Radar is also used to measure distances and map geographical areas (shoran) and to navigate and fix positions at sea. Meteorologists use radar to monitor precipitation; it has become the primary tool for short-term weather forecasting and is also used to watch for severe weather such as thunderstorms and tornados. Radar can be used to study the planets and the solar ionosphere and to trace solar flares and other moving particles in outer space.

Various radar tracking and surveillance systems are used for scientific study and for defense. For the defense of North America the U.S. government developed (c.1959–63) a radar network known as the Ballistic Missile Early Warning System (BMEWS), with radar installations in Thule, Greenland; Clear, Alaska; and Yorkshire, England. A radar system known as Space Detention and Tracking System (SPADATS), operated collaboratively by the Canada and the United States, is used to track earth-orbiting artificial satellites.

See also stealth technology.

Development of Radar

Radar was developed (c.1935–40) independently in several countries as a military instrument for detecting aircraft and ships. One of the earliest practical radar systems was devised (1934–35) by Sir Robert Watson-Watt, a Scots physicist. Although the technology evolved rapidly during World War II, radar improved immensely following the war, the principal advances being higher power outputs, greater receiver sensitivity, and improved timing and signal-processing circuits. In 1946 radar beams from the earth were reflected back from the moon. Radar contact was established with Venus in 1958 and with the sun in 1959, thereby opening a new field of astronomy—radar astronomy.

Bibliography

See G. J. Wheeler, Radar Fundamentals (1967); W. S. Burdic, Radar Signal Analysis (1968); H. Cole, Understanding Radar (1985); M. Skolnik, Radar Handbook (1989).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"radar." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"radar." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/radar

"radar." The Columbia Encyclopedia, 6th ed.. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/radar

Radar

Radar

Radar (a contraction of ra dio d etection a nd r anging) is an electronic system that measures the position, speed, or other characteristics of a far-off object by means of radio waves bounced off the surface of that object. It can pierce any atmospheric disturbance, such as a storm, all the way to the horizon. Within its range, radar can reveal clouds, a landmass, or objects such as ships, airplanes, or spacecraft. Radar can measure distance to a target object; for instance, aircraft use it to determine altitude. Radar is also used to monitor atmospheric systems, to track storms, and to help predict the weather. Military applications include weapons ranging (determining the distance from a weapon to a target) and direction in the control of guided missiles.

Basic radar operation

Light waves, radio waves, microwaves, and radar waves are all examples of electromagnetic waves. Unlike water waves, electromagnetic waves do not require a medium such as water or air to travel through. They can travel through a complete vacuum. Similar to light waves, radar waves bounce off some objects and travel through others.

The simplest mode of radar operation is range-finding, or determining how far away an object is. The radar unit sends radar waves out toward the target (radar systems can send out thousands of pulses per second). The waves hit the target and are reflected back. The returning wave is received by the radar unit, and the travel time is registered. According to basic principles of physics, distance is equal to the rate of travel (speed) multiplied by the time of travel. All electromagnetic waves travel at the same speed in a vacuumthe speed of light, which is 186,282 miles (299,727 kilometers) per second. This speed is reduced by a small amount when the waves are traveling through air, but this can be calculated.

Bats and dolphins are able to emit high-frequency sounds and orient (position) themselves by means of reflected sound waves. This ability is known as echolocation.

Radar and World War II

When the 1930s saw the possibility of a German air invasion, the English government accelerated its research into radar. A chain of radar stations was constructed that would throw an invisible net of radio waves over England. These waves could detect the approach and precise location of any aircraft.

When German dictator Adolf Hitler ordered a massive air strike against England in 1940, the radar shield worked. Although the German air force greatly outnumbered the British Royal Air Force, it was soundly beaten because the radar's eye could easily locate German planes, even in darkness and poor weather.

The military use of radar continued throughout World War II (193945). Compact transmitters were developed that could be mounted

on the underside of a plane to scan the ground far below for targets. Bombs and shells equipped with radar tracking systems were designed to "look" for their targets, exploding at just the right moment.

Other uses of radar

Radar devices began to trickle into everyday use soon after the end of the war. In 1947, a young engineer named John Barker attempted to use radar to regulate traffic lights. He noticed that a passing automobile would reflect a radio pulse, and that the speed of the vehicle could then be determined by examining the returning signal. Much to the dismay of speeders, Barker had devised the first radar speed-gun, now used by police worldwide.

Marine navigators, surveyors, meteorologists, and astronomers have also found uses for radar technology. A continuous-wave version called Doppler radar is often used to track storms and hurricanes. Probes launched into space have used radar to map the surfaces of other planets.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Radar." UXL Encyclopedia of Science. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"Radar." UXL Encyclopedia of Science. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/radar

"Radar." UXL Encyclopedia of Science. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/radar

radar

radar Acronym for radio detection and ranging; the use of electromagnetic energy for the detection of objects which are capable of reflecting it. For example, cloud-detection radars are extensively used in meteorological forecasting and rainfall measurement, while sideways-looking radars are used for topographic mapping. Radar has been used to probe through ice sheets in order to determine ice thickness and to detect internal reflection events; in polar regions the radar equipment has usually been airborne, but the instruments can be mounted on sledges for surface use. Radar can also be used in arid environments to probe through sand in search of water. Ground radar is being developed for use in engineering site investigations, but has very limited depth penetration where the moisture content is high because of the high dielectric loss associated with water.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"radar." A Dictionary of Earth Sciences. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"radar." A Dictionary of Earth Sciences. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/radar

"radar." A Dictionary of Earth Sciences. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/radar

radar

radar (acronym for radio detecting and ranging) Electronic system for determining the direction and distance of objects. Developed during World War II, it works by the transmission of pulses of radio waves to an object. The object reflects the pulses, which are detected by an antenna. By measuring the time it takes for the reflected waves to return, the object's distance may be calculated, and its direction ascertained from the alignment of the receiving radar antenna.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"radar." World Encyclopedia. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"radar." World Encyclopedia. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/radar

"radar." World Encyclopedia. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/radar

radar

ra·dar / ˈrāˌdär/ • n. a system for detecting the presence, direction, distance, and speed of aircraft, ships, and other objects, by sending out pulses of high-frequency electromagnetic waves that are reflected off the object back to the source. ∎  an apparatus used for this. ORIGIN: 1940s: from ra(dio) d(etection) a(nd) r(anging).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"radar." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"radar." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/radar-1

"radar." The Oxford Pocket Dictionary of Current English. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/radar-1

radar

radarDada • radar • zamindar • Pindar •chowkidar • havildar • Godard •doodah •purdah, sirdar

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"radar." Oxford Dictionary of Rhymes. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"radar." Oxford Dictionary of Rhymes. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/radar-0

"radar." Oxford Dictionary of Rhymes. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/radar-0

radar

radar (ˈreɪdɑː) radio detection and ranging

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"radar." The Oxford Dictionary of Abbreviations. . Encyclopedia.com. 14 Dec. 2017 <http://www.encyclopedia.com>.

"radar." The Oxford Dictionary of Abbreviations. . Encyclopedia.com. (December 14, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/radar

"radar." The Oxford Dictionary of Abbreviations. . Retrieved December 14, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/radar