The Earth's atmosphere is divided into several altitude regions. A special case of high Earth orbit is the highly elliptical orbit, where altitude at perigee is less than 2,000 kilometres (1,200 mi). High Earth orbit (HEO) Geocentric orbits with altitudes at apogee higher than that of the geosynchronous orbit. The speed is approximately 3,000 metres per second (9,800 ft/s). The period of the orbit equals one sidereal day, coinciding with the rotation period of the Earth. Geosynchronous orbit (GEO) Geocentric circular orbit with an altitude of 35,786 kilometres (22,236 mi). Medium Earth orbit (MEO) Geocentric orbits with altitudes at apogee ranging between 2,000 kilometres (1,200 mi) and that of the geosynchronous orbit at 35,786 kilometres (22,236 mi). At 160 km, one revolution takes approximately 90 minutes, and the circular orbital speed is 8,000 metres per second (26,000 ft/s). Low Earth orbit (LEO) Geocentric orbits ranging in altitude from 160 kilometers (100 statute miles) to 2,000 kilometres (1,200 mi) above mean sea level. The green dashed line is the 20,230 km orbit used for GPS satellites.

The black dashed line is the geosynchronous orbit. Low (cyan) and Medium (yellow) Earth orbit regions to scale.

Density altitude – the density of the air in terms of altitude in the International Standard Atmosphere in the air.

Pressure altitude – the air pressure in terms of altitude in the International Standard Atmosphere.

Height – vertical distance above a certain point.

True altitude – altitude in terms of elevation above sea level.

Absolute altitude – altitude in terms of the distance above the ground directly below.

Indicated altitude – the altitude shown on the altimeter.

These types of altitude can be explained more simply as various ways of measuring the altitude: 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. Aircraft performance depends on density altitude, which is affected by barometric pressure, humidity and temperature.

Density altitude is the altitude corrected for non-ISA International Standard Atmosphere atmospheric conditions.

Pressure altitude and indicated altitude are the same when the altimeter setting is 29.92' Hg or 1013.25 millibars. Pressure altitude is used to indicate 'flight level' which is the standard for altitude reporting in the Class A airspace (above roughly 18,000 feet).

Pressure altitude is the elevation above a standard datum air-pressure plane (typically, 1013.25 millibars or 29.92' Hg).

Height is the vertical distance above a reference point, commonly the terrain elevation.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).

: ii It is indicated altitude corrected for non-standard temperature and pressure.

True altitude is the actual elevation above mean sea level.

Also referred to as 'radar height' or feet/metres above ground level (AGL). : ii It can be measured using a radar altimeter (or 'absolute altimeter').

Absolute altitude is the vertical distance of the aircraft above the terrain over which it is flying.

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)

Indicated altitude is the reading on the altimeter when it is set to the local barometric pressure at mean sea level.

There are several types of altitude in aviation: 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. When flying at a flight level, the altimeter is always set to standard pressure (29.92 inHg or 1013.25 hPa). So when the altimeter reads the country-specific flight level on the standard pressure setting the aircraft is said to be at 'Flight level XXX/100' (where XXX is the transition altitude).

Pressure altitude divided by 100 feet (30 m) is the flight level, and is used above the transition altitude (18,000 feet (5,500 m) in the US, but may be as low as 3,000 feet (910 m) in other jurisdictions). Īviation altitude is measured using either mean sea level (MSL) or local ground level (above ground level, or AGL) as the reference datum. Parties exchanging altitude information must be clear which definition is being used. 'true altitude'), or implicitly through the context of the communication. In aviation, the term altitude can have several meanings, and is always qualified by explicitly adding a modifier (e.g.

Definiton of altitude geometry