46 Fun Facts About Radar

What does the acronym RADAR stand for?

RADAR stands for radio detection and ranging, a term coined in 1940; it has since become an ordinary lowercase noun.

Which German physicist showed in the 1880s that radio waves reflect off solid objects?

Heinrich Hertz bounced radio waves off metal surfaces in his laboratory, showing that they reflect just as light does and proving Maxwell's theory of electromagnetic waves.

Which German inventor patented the 'telemobiloscope' in 1904 to detect ships in fog?

Christian Hülsmeyer patented his telemobiloscope in 1904; it rang a bell when a ship came within range but could not measure distance, and the German navy declined it.

Which Russian physicist noted in 1897 that a passing ship disturbed radio signals?

Alexander Popov, testing ship-to-ship radio in 1897, noted that a passing vessel disturbed the signal and remarked it might detect objects, but took it no further.

Which vegetable did British wartime propaganda credit for RAF night-fighter kills that were really won by airborne radar?

Carrots, the press was told, gave ace John 'Cat's Eyes' Cunningham his night vision; the cover story stuck, and many Britons came to believe the vegetable helped them see in the dark.

What rumoured German weapon prompted the enquiry that led Britain to radar?

A radio death ray was the rumour the Air Ministry asked about; Arnold Wilkins calculated that it was impossible, then suggested using radio waves to detect aircraft instead.

Whose shortwave transmitter was used for the Daventry Experiment of 26 February 1935?

The BBC's shortwave transmitter at Daventry supplied the signal; a Heyford bomber flew through its beam while Arnold Wilkins's receiver, in a van parked in a field, picked up the echoes.

What did Watson-Watt reportedly exclaim after the Daventry test succeeded?

'Britain has become an island again!' was Watson-Watt's own later account of his words; within days the government had funded the work and sworn the team to secrecy.

What was the codename of Britain's ring of coastal early-warning radar stations?

Chain Home's stations were bombed in August 1940 but most were back on the air within hours, and the Luftwaffe, never grasping how vital they were, soon stopped attacking them.

Where in Suffolk did Britain's radar team develop its coastal warning stations from 1936?

Bawdsey Manor became the Air Ministry's radar research station in 1936; when war broke out in 1939 its scientists were moved to Dundee for fear of a German raid on the exposed coastal site.

Which battle did early warning from coastal radar stations help the RAF to win in 1940?

Battle of Britain pilots could be scrambled only when a raid was seen approaching, instead of flying standing patrols; that use of radar was the core of the 'Dowding system'.

Which two Birmingham physicists built the improved cavity magnetron in 1940?

John Randall and Harry Boot's device gave hundreds of watts at a 10 cm wavelength, a leap in power that let radar sets shrink enough to be carried in aircraft.

What everyday appliance later used the cavity magnetron?

The microwave oven grew out of radar work: in 1945 Raytheon engineer Percy Spencer is said to have noticed a magnetron melting the candy bar in his pocket.

Which 1940 British delegation carried a magnetron to the United States?

The Tizard Mission gave the magnetron away because Britain lacked the factories to exploit it; a US historian called it 'the most valuable cargo ever brought to our shores'.

Which secret wartime US lab, organised by Alfred Loomis, turned Britain's magnetron into working radar sets?

The MIT Radiation Laboratory took a deliberately misleading name: it was chosen to make outsiders think its scientists were doing nuclear physics, not radar.

Where on Oahu's north shore did an Army radar spot the incoming Japanese planes in 1941?

Opana Point's radar crew picked up the raid at 7:02 am, but Lieutenant Kermit Tyler took the blip for B-17 bombers due from the mainland and told them not to worry.

In military radar, what does the abbreviation IFF stand for?

Identification friend or foe uses a transponder that answers a radar's interrogation signal; it was developed in the Second World War after radar arrived and friendly-fire incidents followed.

Which German warship carried an early Seetakt radar when she was scuttled off Montevideo in 1939?

Admiral Graf Spee settled in shallow water after the Battle of the River Plate, leaving the aerial of her radar set standing in plain view above the surface.

Which Cold War radar network stretched across the Arctic from Alaska to Greenland to watch for Soviet bombers?

The DEW Line, short for Distant Early Warning, was finished in 1957 to spot bombers, but it could not see the ballistic missiles that soon became the greater threat.

Which ocean liner had parts of a French obstacle-detecting radio set installed in 1935?

Normandie's detector, an early form of radar, could not save her from a different danger: in 1942 she caught fire and capsized at her New York pier while being converted into a troopship.

What was the British codename for chaff, the metal strips dropped to blind radar?

Window was the British name and Düppel the German; both sides sat on the idea for over a year, each afraid the other would copy it and blind their own radar.

Over which city was the foil countermeasure first used, during Operation Gomorrah in 1943?

Window was first dropped over Hamburg on the night of 24-25 July 1943; German searchlights and flak radars wandered helplessly among the false echoes.

Which German radar was seized and brought to Britain in Operation Biting in 1942?

The Bruneval raid of February 1942 carried off key parts of a Würzburg set; examining its receiver and transmitter showed British scientists how it could be jammed.

What phenomenon lets radar read a target's speed from a change in the returned frequency?

Doppler shift, the effect that makes a passing vehicle's sound drop in pitch, also alters a radar echo's frequency; weather radars use it to track the motion of raindrops, and so the wind.

Which driver-assistance feature usually relies on a forward-facing radar?

Adaptive cruise control slows the car when traffic ahead slows and speeds up again when the road clears; the first systems, sold in Japan in the 1990s, used lasers instead of radar.

Which body did the US Army's Project Diana bounce radar signals off in January 1946?

The Moon gave the project its name, after Rome's moon goddess; each echo came back about two and a half seconds after its pulse left New Jersey, the birth of radar astronomy.

Which lab made the first unambiguous radar contact with Venus, in 1961?

The Jet Propulsion Laboratory's echoes from Venus gave a new, far more precise value for the astronomical unit, just what was needed to steer spacecraft to other planets.

Which giant dish, used to bounce radar off planets and asteroids, collapsed in 2020?

Arecibo's 305 m dish was wrecked when its support cables failed and the instrument platform slung above it crashed down, shortly after officials had ruled it too unsafe to repair.

Whose 1962 Soviet paper on edge waves shaped the design of American stealth aircraft?

Pyotr Ufimtsev's equations were translated by the US Air Force in 1971; Lockheed's Denys Overholser then built them into a program that predicted how flat panels scatter radar.

Which stealth aircraft flew in secret for years before the US Air Force first acknowledged it in November 1988?

The Lockheed F-117 had been operational at a remote Nevada base since 1983; to keep the secret it flew only at night and spent its days shut inside hangars.

What is the measure of how strongly an object scatters radio waves back called?

Cross-section, in radar terms, depends far more on shape than on size: stealth aircraft are said to return an echo no bigger than a small bird's.

A radar signal spreads on the way out and again coming back, so echo power falls with which power of range?

Fourth power: the inverse-square law applies twice, once each way, so doubling a radar's range takes sixteen times the transmitter power.

The Soviet Duga over-the-horizon radar was nicknamed what by shortwave listeners?

Russian Woodpecker was the name radio amateurs gave the sharp, repetitive tapping that broke into shortwave bands worldwide from 1976; the giant aerial was built near Chernobyl.

Which devices displaced the magnetron in many high-power radar transmitters from the 1960s?

Klystrons and travelling-wave tubes amplify a stable reference signal, whereas a magnetron's output jumps in frequency and phase from pulse to pulse, which spoils comparisons between echoes.

Where did the radar band letters such as X, S and L originate?

Wartime code names kept the wavelengths secret: L is said to have stood for 'long' and S for 'short', and the letters were later made official by the IEEE.

Which American research lab built the radio altimeter that United Air Lines introduced in 1938?

Bell Labs engineer Lloyd Espenschied had proposed the idea in the 1920s, but it had to wait about a decade for radio tubes that worked at high enough frequencies.

A radar altimeter measures an aircraft's height above what?

The terrain directly beneath it: the altimeter times a radio beam's trip to the ground and back, which is why automatic landing systems rely on it to start the final flare.

What Oklahoma event of May 1973 was tracked through its whole life cycle by an experimental research radar?

A tornado struck Union City, west of Oklahoma City; the radar data showed rotation in the cloud before the funnel reached the ground, a signature that now buys warning time.

What colour on a weather radar image usually marks the strongest returns?

Red or magenta marks the heaviest echoes; the very strongest usually mean that hail is falling with the rain, a warning forecasters watch for.

Which NASA rover took a ground-penetrating radar to Mars's Jezero Crater in 2021?

Perseverance carries RIMFAX, a radar at its rear that sounds the ground as the rover drives, letting geologists trace buried rock layers without drilling.

What is the rotating map-like radar display that paints echoes as blips called?

The plan position indicator puts the radar at the centre of its own map; fitted to wartime bombers' H2S sets, it showed navigators the towns and rivers below through cloud.

Which laser-based cousin of radar is often used by self-driving cars?

Lidar fires laser pulses instead of radio waves; flown over Guatemala's jungle, it revealed more than 60,000 hidden Maya structures, a find announced in 2018.

Which unexpected source of radio interference, noticed by American researchers in 1930, pushed them towards inventing radar?

A passing aircraft made Lawrence Hyland's signal flutter; his colleagues recalled a ship doing the same on the Potomac in 1922, and this time they followed it up.

Before radar, Robert Watson-Watt worked for Britain's Met Office using radio to locate what for pilots?

Thunderstorms betray themselves by the burst of radio noise in every lightning flash; Watson-Watt took bearings on it, and that radio expertise later brought the Air Ministry to his door.

Which NASA probe mapped the cloud-hidden surface of Venus by radar in the early 1990s?

Magellan was built largely from spare parts left over from earlier probes such as Voyager, then launched from the Space Shuttle Atlantis in 1989.

Which wartime navigation system guided the RAF's Pathfinder force from ground stations in England?

Oboe signals travelled in straight lines from England, so only the fast, high-flying Mosquito could climb high enough to pick them up over Germany and mark targets for the heavy bombers.