An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level.[1] The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water.
Diagram showing the face of the "three-pointer" sensitive aircraft altimeter displaying an altitude of 10,180 ft (3,100 m). Reference pressure of about 29.92 inHg (1013 hPa) is showing in the Kollsman window
Digital barometric pressure sensor for altitude measurement in consumer electronic applicationsAltitude can be determined based on the measurement of atmospheric pressure. The greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is a type of altimeter called a pressure altimeter or barometric altimeter. A pressure altimeter is the altimeter found in most aircraft, and skydivers use wrist-mounted versions for similar purposes. Hikers and mountain climbers use wrist-mounted or hand-held altimeters, in addition to other navigational tools such as a map, magnetic compass, or GPS receiver.
Sonic altimeteredit
In 1931, the US Army Air Corps and General Electric tested a sonic altimeter for aircraft, which was considered more reliable and accurate than one that relied on air pressure when heavy fog or rain was present. The new altimeter used a series of high-pitched sounds like those made by a bat to measure the distance from the aircraft to the surface, which on return to the aircraft was converted to feet shown on a gauge inside the aircraft cockpit.[2]
The altimeter on this Piper PA-28 is seen on the top row of instruments, second from right
A radar altimeter measures altitude more directly, using the time taken for a radio signal to reflect from the surface back to the aircraft. 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 pulsed radar for the same outlay and radar altimeters that use frequency modulation are industry standard. The radar altimeter is used to measure height above ground level during landing in commercial and military aircraft. Radar altimeters are also a component of terrain avoidance warning systems, warning the pilot if the aircraft is flying too low, or if there is rising terrain ahead. Radar altimeter technology is also used in terrain-following radar allowing combat aircraft to fly at very low height above the terrain.
After extensive research and experimentation, it has been shown that "phase radio-altimeters" are most suitable for ground effect vehicles, as compared to laser, isotropic or ultrasonic altimeters.[3]
Laser altimeteredit
Lidar technology is used to help navigate the helicopter Ingenuity on its record-setting flights over the terrain of Mars by means of a downward-facing Lidar altimeter.[4]
Global Positioning Systemedit
Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites. In aircraft, altitude determined using autonomous GPS is not reliable enough to supersede the pressure altimeter without using some method of augmentation.[5] In hiking and climbing, it is common to find that the altitude measured by GPS is off by as much as 400 feet (122 metres) depending on satellite orientation.[6]
Variometer, a gauge measuring the rate of change of altitude
Referencesedit
^Wragg, David W. (1973). A Dictionary of Aviation (1st ed.). Reading: Osprey. p. 33. ISBN0-85045-163-9.
^"Meter Gives Elevation", Popular Science, March 1931
^ Nebylov, Prof. Alexander and Sharan Sukrit. "Comparative Analysis Of Design Variants For Low Altitude Flight Parameters Measuring System". 17th IFAC Symposium for Automatic Control.
^"How NASA Designed a Helicopter That Could Fly Autonomously on Mars". IEEE Spectrum. 17 February 2021. from the original on 19 February 2021. Retrieved 19 February 2021.
^. Garmin. Archived from the original on March 5, 2020. Retrieved March 14, 2020.
External linksedit
Wikimedia Commons has media related to Altimeter.
April 12, 2024
altimeter, confused, with, attitude, indicator, altimeter, altitude, meter, instrument, used, measure, altitude, object, above, fixed, level, measurement, altitude, called, altimetry, which, related, term, bathymetry, measurement, depth, under, water, diagram,. Not to be confused with attitude indicator An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level 1 The measurement of altitude is called altimetry which is related to the term bathymetry the measurement of depth under water Diagram showing the face of the three pointer sensitive aircraft altimeter displaying an altitude of 10 180 ft 3 100 m Reference pressure of about 29 92 inHg 1013 hPa is showing in the Kollsman window Contents 1 Types 1 1 Pressure altimeter 1 2 Sonic altimeter 1 3 Radar altimeter 1 4 Laser altimeter 1 5 Global Positioning System 2 See also 3 References 4 External linksTypes editPressure altimeter edit This section is an excerpt from Pressure altimeter edit nbsp Digital barometric pressure sensor for altitude measurement in consumer electronic applicationsAltitude can be determined based on the measurement of atmospheric pressure The greater the altitude the lower the pressure When a barometer is supplied with a nonlinear calibration so as to indicate altitude the instrument is a type of altimeter called a pressure altimeter or barometric altimeter A pressure altimeter is the altimeter found in most aircraft and skydivers use wrist mounted versions for similar purposes Hikers and mountain climbers use wrist mounted or hand held altimeters in addition to other navigational tools such as a map magnetic compass or GPS receiver Sonic altimeter edit In 1931 the US Army Air Corps and General Electric tested a sonic altimeter for aircraft which was considered more reliable and accurate than one that relied on air pressure when heavy fog or rain was present The new altimeter used a series of high pitched sounds like those made by a bat to measure the distance from the aircraft to the surface which on return to the aircraft was converted to feet shown on a gauge inside the aircraft cockpit 2 Radar altimeter edit Main article Radar altimeter nbsp The altimeter on this Piper PA 28 is seen on the top row of instruments second from rightA radar altimeter measures altitude more directly using the time taken for a radio signal to reflect from the surface back to the aircraft 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 pulsed radar for the same outlay and radar altimeters that use frequency modulation are industry standard The radar altimeter is used to measure height above ground level during landing in commercial and military aircraft Radar altimeters are also a component of terrain avoidance warning systems warning the pilot if the aircraft is flying too low or if there is rising terrain ahead Radar altimeter technology is also used in terrain following radar allowing combat aircraft to fly at very low height above the terrain After extensive research and experimentation it has been shown that phase radio altimeters are most suitable for ground effect vehicles as compared to laser isotropic or ultrasonic altimeters 3 Laser altimeter edit Lidar technology is used to help navigate the helicopter Ingenuity on its record setting flights over the terrain of Mars by means of a downward facing Lidar altimeter 4 Global Positioning System edit Global Positioning System GPS receivers can also determine altitude by trilateration with four or more satellites In aircraft altitude determined using autonomous GPS is not reliable enough to supersede the pressure altimeter without using some method of augmentation 5 In hiking and climbing it is common to find that the altitude measured by GPS is off by as much as 400 feet 122 metres depending on satellite orientation 6 See also editAcronyms and abbreviations in avionics ICAO recommendations on use of the International System of Units Flight instruments Flight level Hypsometer Jason 1 and Ocean Surface Topography Mission Jason 2 are satellite missions that use altimeters to measure sea surface height Level sensor Lidar Pressure sensor Primary flight display Radar altimeter Satellite altimetry Turkish Airlines Flight 1951 an accident attributed to a malfunctioning radio altimeter United Airlines Flight 389 an accident attributed to misreading of an altimeter Variometer a gauge measuring the rate of change of altitudeReferences edit Wragg David W 1973 A Dictionary of Aviation 1st ed Reading Osprey p 33 ISBN 0 85045 163 9 Meter Gives Elevation Popular Science March 1931 Nebylov Prof Alexander and Sharan Sukrit Comparative Analysis Of Design Variants For Low Altitude Flight Parameters Measuring System 17th IFAC Symposium for Automatic Control How NASA Designed a Helicopter That Could Fly Autonomously on Mars IEEE Spectrum 17 February 2021 Archived from the original on 19 February 2021 Retrieved 19 February 2021 Alberi Matteo Baldoncini Marica Bottardi Carlo Chiarelli Enrico Fiorentini Giovanni Raptis Kassandra Giulia Cristina Realini Eugenio Reguzzoni Mirko Rossi Lorenzo Sampietro Daniele Strati Virginia Mantovani Fabio 16 August 2017 Accuracy of Flight Altitude Measured with Low Cost GNSS Radar and Barometer Sensors Implications for Airborne Radiometric Surveys Sensors 17 8 1889 arXiv 1802 00327 Bibcode 2017Senso 17 1889A doi 10 3390 s17081889 PMC 5579878 PMID 28813023 Understanding the Accuracy of the GPS Elevation Reading Garmin Archived from the original on March 5 2020 Retrieved March 14 2020 External links edit nbsp Wikimedia Commons has media related to Altimeter Retrieved from https en wikipedia org w index php title Altimeter amp oldid 1178523279 Pressure altimeter, wikipedia, wiki, book, books, library,
