Height measured with respect to the underlying ground surface
In aviation, atmospheric sciences and broadcasting, a height above ground level (AGL[1] or HAGL) is a height measured with respect to the underlying ground surface. This is as opposed to height above mean sea level (AMSL or HAMSL), height above ellipsoid (HAE, as reported by a GPS receiver), or height above average terrain (AAT or HAAT, in broadcast engineering). In other words, these expressions (AGL, AMSL, HAE, AAT) indicate where the "zero level" or "reference altitude" – the vertical datum – is located.
Abbreviation
Stands for
Main usage
Zero level
Measuring devices
AGL, HAGL
height above ground level
aviation, atmospheric science, broadcasting
ground surface
radar altimeter
AMSL, HAMSL
height above mean sea level
nautic, technics, geography
sea level average
barometric altimeter
HAE
height above ellipsoid
navigation, science
math surface model WGS84
GPS receiver
AAT, HAAT
height above average terrain
broadcasting, cellular networks
average surrounding surface
^Radiotelephony Manual. UK Civil Aviation Authority. 28 May 2015. ISBN 9780-11792-893-0. CAP413.
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