RADAR/ RADIO            2013FLIGHT INSTRUMENTS & RADIO NAVIGATIONAL AIDS              ALTIMETER    RADAR/ RADIO      ALTIM...
RADAR/ RADIO ALTIMETER                                                                                                    ...
RADAR/ RADIO ALTIMETER                                                            2013A LTIMETER               An altimete...
RADAR/ RADIO ALTIMETER                                                         2013             QNH:             The regio...
RADAR/ RADIO ALTIMETER                                                          2013R ADAR ALTIMETER          WORKS ON ONE...
RADAR/ RADIO ALTIMETER                                                         2013C IVIL APPLICATIONS OF R ADAR A LTIMETE...
RADAR/ RADIO ALTIMETER                                                          2013   R ADAR ALTIMETERS CANN OT SEE TERRA...
RADAR/ RADIO ALTIMETER                                                           2013              2. Decision Height Bug....
RADAR/ RADIO ALTIMETER                                                           2013I NDICATIONS           Indicator give...
RADAR/ RADIO ALTIMETER                                                         2013A PPLICATION   OF RADAR ALTIMETERS     ...
RADAR/ RADIO ALTIMETER                                                           2013          distance by the size of the...
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Radar altimeter assignment

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  1. 1. RADAR/ RADIO 2013FLIGHT INSTRUMENTS & RADIO NAVIGATIONAL AIDS ALTIMETER RADAR/ RADIO ALTIMETER SUBMITTED TO: SIR SAQIB SUBMITTED BY: BILAL AHMAD MEHMAN ALI BILAL AHMAD 2013 University of Management & Technology
  2. 2. RADAR/ RADIO ALTIMETER 2013 T ABLE OF C ONTENTSAltimeter ........................................................................................................................................................................2Types of altimeter ..........................................................................................................................................................2 1. Barometric/ pressure altimeter ..........................................................................................................................2 2. Radio/radar altimeter ........................................................................................................................................3Invention ........................................................................................................................................................................3Radar altimeter works on one of two methods ..............................................................................................................4 1. Pulse modulated radar ......................................................................................................................................4 2. Frequency modulated continuous wave FMCW radar .....................................................................................4Civil applications of Radar Altimeter .............................................................................................................................5Military applications ......................................................................................................................................................5Radio altimeters are an essential part in ground proximity warning systems (GPWS) .................................................5 Radar altimeters cannot see terrain directly ahead of the aircraft ...........................................................................6 Radar/radio altimeter antennas ................................................................................................................................6Components of Radar Altimeter ....................................................................................................................................6Frequency Used in radar altimeter .................................................................................................................................7Principle of Radar Altimeter ..........................................................................................................................................7Indications .....................................................................................................................................................................8Accuracy of radio altimeter ...........................................................................................................................................8Operations......................................................................................................................................................................8Application of radar altimeters ......................................................................................................................................9Summary........................................................................................................................................................................9 1|P a g e
  3. 3. RADAR/ RADIO ALTIMETER 2013A LTIMETER An altimeter or an altitude meter is an instrument used to measure the altitude of an object (aircraft) above a fixed level. This fixed level may be the sea level, ground level or a specified datum in atmosphere. The measurement of altitude is called altimetry.T YPES OF ALTIMETER There are two basic types of altimeter 1. Barometric/ pressure altimeter 2. Radar/ radio altimeter 1. B AROMETRIC / PRESSURE ALTIMETER F IGURE 1 F IGURE 2 F IGURE 3 Pressure altimeter measures the weight of column of air above aircraft. The higher the aircraft the shorter is the column of air above it and consequently the lower is the atmospheric pressure on the aircraft.Altitude can be determined based on the measurement of atmospheric pressure. The greater the altitude the lower the pressure.In aircraft, an aneroid barometer measures the atmospheric pressure from a static port outside the aircraft. Air pressure decreases with an increase of altitude— approximately 100 hectopascals per 800 meters. 2|P a g e
  4. 4. RADAR/ RADIO ALTIMETER 2013 QNH: The regional or local air pressure at mean sea level (MSL) is called the QNH. QFE The pressure that will calibrate the altimeter to show the height above ground at a given airfield is called the QFE of the field.i QNE Barometric pressure used for standard altimeter (29.92) For instance, when you pass through transition layer, you set QNEii 2. R ADIO / RADAR ALTIMETER A radar altimeter, radio altimeter, low range radio altimeter (LRRA) or simply RA measures altitude above the terrain presently beneath an aircraft or spacecraft. This type of altimeter provides the distance between the plane and the ground directly below it, as opposed to a barometric altimeter which provides the distance above a pre-determined datum, usually sea level.Short- range radio altimeters are important safety and navigational tools in small aircraft. Usually designed as short-range frequency-modulated (FM) radars in the 4.2-to-4.4-GHz,I NVENTION In 1924, American engineer Lloyd Espenschied invented the radio altimeter. However, it took 14 years before Bell Labs was able to put Espenschieds device in a form that was adaptable for aircraft use. In 1938 in co-operation with Bell Labs, United Air Lines fitted a radar type device to some of its airliners as a terrain avoidance device.iii 3|P a g e
  5. 5. RADAR/ RADIO ALTIMETER 2013R ADAR ALTIMETER WORKS ON ONE OF TWOMETHODS 1. Pulse modulated radar 2. Frequency modulated continuous wave FMCW radar 1. P ULSE MODULATED RADAR It is a form of radar in which the radiation consists of a series of discrete pulses. iv The original and underlying method is by transmitting radio waves downward, and interpreting the time it takes for the waves to reflect back as a function of distance. 2. F REQUENCY MODULATED CONTINUOUS WAVE FMCW RADAR Frequency-modulated continuous-wave radar (FM-CW) is short range measuring radar set capable of determining distance. This increases reliability by providing distance measurement along with speed measurement, which is essential when there is more than one source of reflection arriving at the radar antenna. This kind of radar is used to measure the exact height during the landing procedure of aircraft. It is also used as early-warning radar, and proximity sensors.v The difference in frequency between that received from the ground and that being transmitted is a measure of the time delay. The greater the shift the further the distance travelled. FMCW radar altimeter is the industry standard. Frequency modulated continuous-wave (FMCW) radar, which sends out a continuous transmission wave and measures distance by the size of the shift in the signals frequency. (For example in binary system we have 0 and 1; the conversion from 0 to 1 or 1 to 0 is called a shift.) FMCW is considered a much more accurate and therefore safer technology.vi (Note: In this document we will consider the FMCW radar altimeter) 4|P a g e
  6. 6. RADAR/ RADIO ALTIMETER 2013C IVIL APPLICATIONS OF R ADAR A LTIMETER Radar altimeters are frequently used by commercial aircraft for approach and landing, especially in low-visibility conditions and also in automatic landings, allowing the autopilot to know when to begin the flare maneuver. Radar Altimeters give data to the auto throttle. In civil aviation applications, radio altimeters generally only give readings up to 2,500 feet (760 m) above ground level (AGL). Today, almost all airliners are equipped with at least one and usually several radar altimeters, as they are essential to autoland capabilities (determining height through other methods such as GPS is not permissible under current legislation). Even older airliners from the 1960s, such as Concorde and the British Aircraft Corporation BAC 1-11 were so equipped and today even smaller airliners in the sub-50 seat class are supplied with them (such as the ATR 42 and BAe Jetstream series).M ILITARY APPLICATIONS Radar altimeters are also used in military aircraft to fly quite low over the land and the sea to avoid radar detection and targeting by anti-aircraft guns or surface-to-air missiles. A related use of radar altimeter technology is terrain-following radar, which allows fighter bombers to fly at extremely low altitudes. In modern fighter aircrafts, forward terrain looking radars are also used. Similar systems are now used by the F/A-18 Super Hornet warplanes flown by the Americans and by the Australians.R ADIO ALTIMETERS ARE AN ESSENTIAL PART INGROUND PROXIMITY WARNING SYSTEMS (GPWS) Radio altimeters are an essential part in ground proximity warning systems (GPWS), warning the pilot if the aircraft is flying too low or descending too quickly. 5|P a g e
  7. 7. RADAR/ RADIO ALTIMETER 2013 R ADAR ALTIMETERS CANN OT SEE TERRAIN DIREC TLY AHEAD OF THE AIRCRAFT However, radar altimeters cannot see terrain directly ahead of the aircraft, only that directly below it; such functionality requires either knowledge of position and the terrain at that position or forward looking terrain radar which uses technology similar to a radio altimeter. R ADAR / RADIO ALTIMETER ANTENNAS Radio altimeter antennas have a fairly large main lobe of about 80° so that up to bank angles of about 40°, the radio altimeter detects the range from the aircraft down to the ground, specifically to the nearest large reflecting object. This is because range is calculated based on the first signal return from each sampling period. It does not detect slant range until beyond about 40° of bank or pitch. This is not an issue for landing as pitch and roll do not normally exceed 20° or so during approach and landing.C OMPONENTS OF R ADAR A LTIMETER 1. DH Annunciator 2. Decision Height Bug 3. Failure Warning Flag 4. Altitude Pointer 5. DH SET Knob 6. TEST Push Button 1. Decision Height (DH) Annunciator. The DH annunciator will illuminate when the aircraft is at or below the selected decision height. 6|P a g e
  8. 8. RADAR/ RADIO ALTIMETER 2013 2. Decision Height Bug. The decision height bug is set to the desired decision height, by the DH SET knob. 3. Failure Warning Flag. The OFF warning flag will be in view whenever the system information is unreliable. 4. Altitude Pointer. The altitude pointer will point to the existing altitude. 5. DH SET Knob. The DH SET knob is used to set the decision height bug to the desired DH. 6. TEST Push Button. When pressed, the OFF warning flag will come in to view and the altitude pointer will indicate approximately 100 feet. Release of the button will cause the altitude pointer to return to existing altitude, and OFF warning flag to retract.vii Note: the components may be different for different radar altimeters used in different aircrafts and helicopters.F REQUENCY U SED IN RADAR ALTIMETER 4200-4400MHz. It uses super high frequency SHF band.P RINCIPLE OF R ADAR A LTIMETER It works on the principle of Frequency modulated continuous wave. As the name implies, radar (radio detection and ranging) is the underneath principle of the system. Radio waves are transmitted towards the ground and the time it takes them to be reflected back and return to the aircraft is timed. Because speed, distance and time are all related to each other, 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. Alternatively, Frequency Modulated Continuous-wave radar can be used. The greater the frequency shift the further the distance travelled. This method can achieve much better accuracy than the aforementioned for the same outlay and radar altimeters that use frequency modulation are industry standard. 7|P a g e
  9. 9. RADAR/ RADIO ALTIMETER 2013I NDICATIONS Indicator gives height of aircraft up to 2500’ in steps of 5’ with aircraft in landing attitude i.e. landing gear down.A CCURACY OF RADIO ALTIMETER ± (3%+5’) in landing attitudeviiiO PERATIONS The basic operation of a radio altimeter is shown in Fig. It is a low-power, continuous-wave (CW) radar system that generally requires separate transmit and receive antennas. 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 reliable. Most aviation radio altimeters have separate transmit and receive antennas although considerable efforts were invested into developing a single-antenna radio altimeter. 8|P a g e
  10. 10. RADAR/ RADIO ALTIMETER 2013A PPLICATION OF RADAR ALTIMETERS Their main applications are for instrument-based approaches and landings for larger commercial aircraft, although they are also suitable for smaller aircraft and even unmanned air vehicles (UAVs).S UMMARY Also known as a radar altimeter, a radio altimeter is a device that is used to measure the distance beneath the craft in which it is mounted, usually an airplane or helicopter, and the ground. Unlike a barometric altimeter, which measures altitude from a given height, typically sea level, a radio altimeter measures the distance between the aircraft and the terrain directly below it. Invented in 1924, radio altimeters did not see widespread use until much later, but are now common in commercial and unprofessional flight for landing maneuvers and low-altitude navigation. Functionally, a radio/radar altimeter works in one of two ways. The original and underlying method is by transmitting radio waves downward, and interpreting the time it takes for the waves to reflect back as a function of distance (pulse modulated radar altimeter. The second way, which is the industry standard, is via frequency modulated continuous-wave (FMCW) radar, which sends out a continuous transmission wave and measures 9|P a g e
  11. 11. RADAR/ RADIO ALTIMETER 2013 distance by the size of the shift in the signals frequency. FMCW is considered a much more accurate and therefore safer technology.ix i http://en.wikipedia.org/wiki/Altimeter ii http://www.airliners.net/aviation-forums/general_aviation/read.main/444886/ iii http://www.answers.com/topic/radar-altimeter#Principle iv http://www.answers.com/topic/pulse-modulated-radar v http://en.wikipedia.org/wiki/Continuous-wave_radar#Modulated_continuous-wave vi http://www.wisegeek.com/what-is-a-radio-altimeter.htm vii http://aviationandaccessories.tpub.com/TM-1-1510-218-10/css/TM-1-1510-218- 10_303.htm viii http://www.flying-geeks.com/notes/radio-altimeter/ ix http://www.wisegeek.com/what-is-a-radio-altimeter.htm 10 | P a g e

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