Radar altimeter presentation

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ALTIMETERBarometric Altimeter QNH QFE QNE Radar altimeter

RADIORADARInvented In 1924 by Lloyd ESPENSCHIED

In 1938, in cooperation with Bell Labs, United Air Lines used it as a terrain avoidance device

Radio detection and ranging.1

RADAR ALTIMETERProvides distance between plane and ground below it

RADIO ALTIMETER

5.2.4.3.1.Measures altitude above the terrain

LRRA

RA

LOW RANGE RADIO ALTIMITER

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DH AnnunciatorDecision Height Bug

Failure Warning FlagAltitude Pointer

TEST Push ButtonDH SET Knob COMPONENTS

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Accuracy: (3%+5) in landing attitudeFrequency: 4200-4400MHz It uses SHF band

Between 3000-30,000 MHz9

Antenna has a lobe of about 80

It can detect height correctly up to bank angles of about 40

For landing as pitch and roll do not normally exceed 20Radar Altimeter Antenna

In radio electronics, especially radar terminology, slant range is the line-of-sight distance between two points which are not at the same level relative to a specific datum.10

METHODS USE IN RADAR ALTIMETRY Radiation consists of a series of discrete pulsesBy transmitting radio waves downwardInterpreting the time it takes for the waves to reflect back

Sends out a continuous transmission waveDistance = size of shift in signal's frequencyThe greater the shift the further the distance travelledGround proximity warning1.Pulse modulated radar2.FMCW

For example in binary system we have 0 and 1; the conversion from 0 to 1 or 1 to 0 is called a shift11

OPERATION It is a CW radar system Separate transmit and receive antennasSingle antenna is not reliable

The radio-wave propagation delay is usually too short to switch a single antenna between the transmitter and the receiver. That is why single antenna is not reliable12

Principle Of Radar Altimeter

Frequency modulated continuous waveIt uses the principle of RADARSpeed, distance and time are relatedS=VT

Radio waves are transmitted towards the ground and the time it takes them to be reflected back and return to the aircraft is timed

The distance from the surface providing the reflection can be calculated as the speed of the radio wave and therefore the time it takes to travel a distance are known quantities S=VT

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Military Applications1To fly quite low over the land and the seaTo avoid radar detection To avoid targeting by anti-aircraft gunsTo avoid surface-to-air missiles Terrain-following radar, which allows fighter bombers to fly at extremely low altitudesIn modern fighter aircrafts, forward terrain looking radars are also used F/A-18 Super Hornet warplanes flown by the Americans and by the Australians234567For approach and landingIn low-visibility conditionsIn automatic landingsAllowing the autopilot to know when to begin the flare maneuver Radar Altimeters give data to the auto throttleGive readings up to 2,500 feet (AGL)Almost all airliners are equipped with radar altimetersConcorde and the British Aircraft Corporation BAC 1-11ATR 42 and BAE Jetstream series)1Civil Application23456789

(determining height through other methods such as GPS is not permissible under current legislation)

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