Altitude
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 the
United States, the
UK and
aviation 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
aneroid barometer calibrated to indicate altitude instead of pressure. It is the fall in pressure that leads to a shortage of oxygen (
hypoxia) in humans on ascent to high altitude.
(Altitude pressure calculator)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.
(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; this is referred to over the radio as
altitude. (see
QNH)
(CAP413)*
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; this is referred to over the radio as
height, where the specified datum is the airfield elevation (see
QFE)
(CAP413)*
Indicated altitude is the reading on the altimeter.
*
Pressure altitude is the elevation above a standard datum plane (typically, 1013.2 millibars). Pressure altitude divided by 100 feet is referred to as the
flight level; so when the altimeter reads 18,000 ft on the standard pressure setting the aircraft is said to be at "Flight level 180". Below FL180, altitudes are read in thousands, pronounced "one three thousand" for 13,000, "seven thousand" for 7,000 etc.
*
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.
*
Absolute altitude is the height of the aircraft above the terrain over which it is flying.
Mountain medicine recognizes three altitude regions:
(Non-Physician Altitude Tutorial)* High altitude = 1500 m – 3500 m
* Very High altitude = 3500 m – 5500 m
* Extreme altitude = 5500 m – aboveTravel to high altitudes leads to a range of medical problems, from the relatively mild symptoms of
acute mountain sickness to the potentially fatal
high altitude pulmonary oedema (
HAPE) and
high altitude cerebral oedema (
HAPE). These conditions are caused by the profound
hypoxia associated with travel to high altitudes.The
Earth's atmosphere is divided into several altitude regions:
(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
* August 1783 — 24 m Jean Francois Pilatre in a bot-air balloon.
* 15 October, 1783 — 26 m
Pilâtre de Rozier in a
Montgolfier tethered balloon.
* 1 December, 1783 — 610 m
Professor Charles and assistant Robert in Charliere, his hydrogen-filled balloon.
* 1 December, 1783 — 2.7 km
Professor Charles in Charliere, his hydrogen-filled balloon.
* 1784 — 4 km
Pilâtre 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 and
Spencer Rush in a free balloon.
* 5 September, 1862 — 11.887 km
Coxwell and English physicist
Glaisher in a balloon.
* November 1927 — 13.222 km Captain Hawthorne C. Gray of the US Army Air Corps. in a balloon.
* 27 May 1931 — 15.787 km Auguste Piccard & Paul Kipfer in a hydrogen balloon.
* 1932 — 16.2 km Auguste Piccard & Max Cosyns in a hydrogen balloon.
* 30 September 1933 — 18.501 km USSR balloon.
* 20 November 1933 — 18.592 km Auguste & Jean Piccard in Century of Progress balloon.
* 30 January 1934 — 21.946 km USSR balloon.
* 10 November 1935 — 22.066 km Anderson & Stevens in Explorer II.
* 4 May 1961 — 34.668 km Victor Prather & Malcolm Ross of the US Navy in Strato-Lab V, a zero-pressure balloon.
* 17 July 1962 — 95.94 km Robert White in an
X-15 aircraft.
* 19 July 1963 — 106.01 km Joseph Walker in an
X-15 aircraft.
* 22 August 1963 — 107.96 km Joseph Walker in an
X-15 aircraft.
*
*
Downloadable ETOPO2 Raw Data Database (2 minute grid)*
Downloadable ETOPO5 Raw Data Database (5 minute grid)*
Altitude sickness
