Altitude

high altitudealtitudeshigh-altitudecruising altitudeheightAaltitudinalelevationhigh elevationhigh altitudes
Altitude or height (sometimes known as 'depth') is defined based on the context in which it is used (aviation, geometry, geographical survey, sport, atmospheric pressure, and many more).wikipedia
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Height

tallhhigh
Altitude or height (sometimes known as 'depth') is defined based on the context in which it is used (aviation, geometry, geographical survey, sport, atmospheric pressure, and many more).
When the term is used to describe vertical position (of, e.g., an airplane) from sea level, height is more often called altitude.

Altimeter

altimetrybarometric altimeterpressure altimeter
On the flight deck, the definitive instrument for measuring altitude is the pressure altimeter, which is an aneroid barometer with a front face indicating distance (feet or metres) instead of atmospheric pressure.
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level.

Metres above sea level

above sea levelaslabove mean sea level
Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.
Metres above mean sea level (MAMSL) or simply metres above sea level (MASL or m a.s.l.) is a standard metric measurement in metres of vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum.

Elevation

hightopographic elevationelevated
Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.
The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface.

Barometer

barometricaneroid barometerbarometers
On the flight deck, the definitive instrument for measuring altitude is the pressure altimeter, which is an aneroid barometer with a front face indicating distance (feet or metres) instead of atmospheric pressure.
An altimeter is intended to be used at different levels matching the corresponding atmospheric pressure to the altitude, while a barometer is kept at the same level and measures subtle pressure changes caused by weather.

Radar altimeter

radio altimeterradar altimetryelectronic altimeter
Absolute altitude is the vertical distance of the aircraft above the terrain over which it is flying. It can be measured using a radar altimeter (or "absolute altimeter"). Also referred to as "radar height" or feet/metres above ground level (AGL).
A radar altimeter, electronic altimeter, reflection altimeter, radio altimeter (RADALT), low range radio altimeter (LRRA) or simply RA, used on aircraft, measures altitude above the terrain presently beneath an aircraft or spacecraft by timing how long it takes a beam of radio waves to reflect from the ground and return to the plane.

Geodetic datum

datumGeodeticinitial point
As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object.
Each starts with an ellipsoid (stretched sphere), and then defines latitude, longitude and altitude coordinates.

Density altitude

altitudesthin mountain air
Density altitude is the altitude corrected for non-ISA International Standard Atmosphere atmospheric conditions. Aircraft performance depends on density altitude, which is affected by barometric pressure, humidity and temperature. On a very hot day, density altitude at an airport (especially one at a high elevation) may be so high as to preclude takeoff, particularly for helicopters or a heavily loaded aircraft.
The density altitude is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation.

Kármán line

edge of spaceboundary of spacespace
The Kármán line, at an altitude of 100 km above sea level, by convention defines represents the demarcation between the atmosphere and space.
The Fédération aéronautique internationale (FAI; English: World Air Sports Federation), an international standard-setting and record-keeping body for aeronautics and astronautics, defines the Kármán line as the altitude of 100 km above Earth's sea level.

Height above ground level

AGLabove ground levelaltitude
Absolute altitude is the vertical distance of the aircraft above the terrain over which it is flying. It can be measured using a radar altimeter (or "absolute altimeter"). Also referred to as "radar height" or feet/metres above ground level (AGL).
Therefore, the pilot needs reliable information on the height of the plane with respect to the landing area (usually an airport).

Troposphere

troposphericdivergencemid-tropospheric
Troposphere: surface to 8000 m at the poles, 18000 m at the Equator, ending at the Tropopause
The temperature of the troposphere decreases with altitude.

Lapse rate

adiabatic lapse ratedry adiabatic lapse rateadiabatic
The rate of decrease of temperature with elevation is known as the adiabatic lapse rate, which is approximately 9.8 °C per kilometer (or 5.4 °F per 1000 feet) of altitude.
The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, changes with altitude.

Altitude sickness

acute mountain sicknesshigh altitude sicknessmountain sickness
The lack of oxygen above 8000 ft can cause serious illnesses such as altitude sickness, high altitude pulmonary edema, and high altitude cerebral edema.
Altitude sickness, the mildest form being acute mountain sickness (AMS), is the negative health effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation.

International Standard Atmosphere

ISAstandard atmosphereInternational standard
Density altitude is the altitude corrected for non-ISA International Standard Atmosphere atmospheric conditions. Aircraft performance depends on density altitude, which is affected by barometric pressure, humidity and temperature. On a very hot day, density altitude at an airport (especially one at a high elevation) may be so high as to preclude takeoff, particularly for helicopters or a heavily loaded aircraft.
The International Standard Atmosphere (ISA) is a static atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations.

Organisms at high altitude

high-altitude adaptationadaptation to high altitudesadapted at high altitudes
Despite these environmental conditions, many species have been successfully adapted at high altitudes.
Organisms can live at high altitude, either on land, in water, or while flying.

Altitude training

high-altitude traininghigh altitudeto prepare for this factor
These changes are the basis of altitude training which forms an integral part of the training of athletes in a number of endurance sports including track and field, distance running, triathlon, cycling and swimming.
Altitude training is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 8000 ft above sea level, though more commonly at intermediate altitudes due to the shortage of suitable high-altitude locations.

Effects of high altitude on humans

death zonehigh altitudealtitude acclimatization
The human body can adapt to high altitude by breathing faster, having a higher heart rate, and adjusting its blood chemistry.
The death zone, in mountaineering, refers to altitudes above a certain point where the amount of oxygen is insufficient to sustain human life for an extended time span.

Mesosphere

upper atmospherenear spacemesospheric
Mesosphere: Stratosphere to 85 km
In the mesosphere, temperature decreases as the altitude increases.

Atmosphere of Earth

airatmosphereEarth's atmosphere
The Earth's atmosphere is divided into several altitude regions.
It extends from Earth's surface to an average height of about, although this altitude varies from about at the geographic poles to at the Equator, with some variation due to weather.

Coffin corner (aerodynamics)

coffin corner
Coffin corner (aerodynamics) At higher altitudes, the air density is lower than at sea level. At a certain altitude it is very difficult to keep an airplane in stable flight.
At higher altitudes, the air density is lower than at sea level.

Vertical metre

Hm
Vertical metre
Altitude of aircraft above ground level

Geography

geographicalgeographicgeographer
Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.

Pressure altitude

altitude
Pressure altitude divided by 100 feet (30 m) is the flight level, and is used above the transition altitude (18000 ft in the US, but may be as low as 3000 ft in other jurisdictions); so when the altimeter reads 18,000 ft on the standard pressure setting the aircraft is said to be at "Flight level 180".

Flight level

FLtransition altitudetransition level
Pressure altitude divided by 100 feet (30 m) is the flight level, and is used above the transition altitude (18000 ft in the US, but may be as low as 3000 ft in other jurisdictions); so when the altimeter reads 18,000 ft on the standard pressure setting the aircraft is said to be at "Flight level 180".

Inch of mercury

inHginches of mercuryinches
When flying at a flight level, the altimeter is always set to standard pressure (29.92 inHg or 1013.25 hPa).