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Altitude

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:''For other uses see Altitude (disambiguation)'' '''Altitude''' is the elevation of an object from a known level or datum. Common datums are mean sea level and the surface of the WGS-84 geoid, used by GPS. In North America and the United Kingdom UK altitude is usually measured in feet. Everywhere else in the world the altitude is measured in metres. Atmospheric pressure decreases with altitude. This principle is the basis of operation of the pressure altimeter, which is an barometer#Aneroid barometers aneroid barometer calibrated to indicate altitude instead of pressure.

Altitude in aviation
In aviation, the term '''altitude''' can have several meanings. It is a fundamental tenet of flight safety that both parties exchanging information concerning this topic are absolutely clear which definition is being used. #References (AFM 51-40) *'''True altitude''' is the elevation above mean sea level. In UK aviation radiotelephony usage, ''the vertical distance of a level, a point or an object considered as a point, measured from mean sea level''; below the Transition Level this is referred to over the radio as '''altitude'''. #References (CAP413) *'''Absolute altitude''' or '''height''' is the elevation above a ground reference point, commonly the terrain elevation. In UK aviation radiotelephony usage, ''the vertical distance of a level, a point or an object considered as a point, measured from a specified datum''; below the Transition Level this is referred to over the radio as '''height''', where the specified datum is the airfield elevation. #References (CAP413) *'''Indicated altitude''' is the reading on the altimeter when it is calibrated to the local barometric pressure, referred to as the "altimeter setting". (See also QNH and QFE). *'''Pressure altitude''' is the elevation above a standard datum plane (typically, 1013.2 millibars). Above a Transition Altitude transition altitude, which varies by nation, pressure altitude is used to set the altimeter. Pressure altitude divided by 100 is referred to as the flight level. *'''Density altitude''' is the altitude in the International Standard Atmosphere (ISA) at which the air density is equal to local conditions. Aircraft performance depends on density altitude, which is affected by barometric pressure and temperature. On a very hot day, density altitude at an airport may be so high as to preclude takeoff, particularly for helicopters or a heavily loaded aircraft.

Altitude regions
Mountain medicine recognizes three altitude regions: #References (Non-Physician Altitude Tutorial) * High altitude = 1500 m – 3500 m * Very High altitude = 3500 m – 5500 m * Extreme altitude = 5500 m – above The Earth's atmosphere is divided into several altitude regions: #References (Layers of the Atmosphere) * Troposphere — surface to 8 km (above poles) – 18 km (above equator), ending at the Tropopause. * Stratosphere — Tropopause to 31 miles * Mesosphere — Stratopause to 53 miles * Thermosphere — Mesopause to 420 miles * Exosphere — Thermopause to 6200 miles

Altitude records
{{Cleanup-verify}} * 19 September, 1783 — 500 m (1,700ft) animal carrying Montgolfier hot-air balloon. * 15 October, 1783 — 26 m (84ft) PilÃ¢tre de Rozier in a Montgolfier tethered balloon. * 1 December, 1783 — 2.7 km Professor Charles and assistant Robert in Charliere, his hydrogen-filled balloon. * 1784 — 4 km PilÃ¢tre de Rozier and the chemist Proust in a Montgolfier. * 18 July, 1803 — 7.28 km Etienne Gaspar Robertson and Lhoest in a balloon. * 1839 — 7.9 km Charles Green (balloonist) Charles Green and Spencer Rush in a free balloon. * 5 September, 1862 — 9 km Coxwell and English physicist James Glaisher Glaisher in a balloon. * 4 December, 1894 — 9.155 km German meteorologist Berson in an airship. * 31 July, 1901 — 10.8 km German meteorologist Berson and SÃ¼ring in a free balloon.

References
*{{cite book | year=1 December 1989 | title=Air Navigation |publisher=Department of the Air Force| id=AFM 51-40 }} *{{cite book | year=1 January 1995 | title=Radiotelephony Manual |publisher=UK Civil Aviation Authority| id=CAP413| ISBN=0860396010 }} *{{cite web | title=Non-Physician Altitude Tutorial | publisher=International Society for Mountain Medicine | url=http://www.ismmed.org/np_altitude_tutorial.htm | accessdate=22 December | accessyear=2005}} *{{cite web | title=Layers of the Atmosphere |work=JetStream, the National Weather Service Online Weather School | publisher=National Weather Service | url=http://www.srh.noaa.gov/srh/jetstream/atmos/layers.htm | accessdate=22 December | accessyear=2005}}

External links
*{{cite web | title=The Race to the Stratosphere | publisher=U.S. Centennial of Flight Commission | url=http://www.centennialofflight.gov/essay/Lighter_than_air/race_to_strato/LTA11.htm | accessdate=25 January | accessyear=2006 }}
- Downloadable ETOPO2 Raw Data Database (2 minute grid)
- Downloadable ETOPO5 Raw Data Database (5 minute grid)

See also
* Altitude sickness Category:Physical geography ast:AltitÃº bg:Ð?Ð°Ð´Ð¼Ð¾Ñ€Ñ?ÐºÐ° Ð²Ð¸Ñ?Ð¾Ñ‡Ð¸Ð½Ð° ca:Altitud de:HÃ¶he es:Altitud eo:Alto fr:Altitude gl:Altura it:Altitudine hu:MagassÃ¡g nl:Hoogte ja:é«˜ã?• ru:Ð’Ñ‹Ñ?Ð¾Ñ‚Ð° Ð½Ð°Ð´ ÑƒÑ€Ð¾Ð²Ð½ÐµÐ¼ Ð¼Ð¾Ñ€Ñ? simple:Height sr:Ð?Ð°Ð´Ð¼Ð¾Ñ€Ñ?ÐºÐ° Ð²Ð¸Ñ?Ð¸Ð½Ð° sv:Altitud tl:Altitud zh:æµ·æ‹”

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