ImportMaster at 20:17, 31 January 2022

2022-01-31T20:17:51Z

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{{short description|Elevation of a location in reference to a historic mean sea level taken as a vertical datum}}
{{redirect|AMSL|the Canadian soccer league|Alberta Major Soccer League|the Airbus company|Airbus Military}}
{{refimprove|date=August 2019}}

'''Height above mean sea level''' is a measure of the [[Vertical position|vertical distance]] ([[height]], [[elevation]] or [[altitude]]) of a location in reference to a historic [[mean sea level]] taken as a [[vertical datum]]. In [[geodesy]], it is formalized as ''[[orthometric height]]s''.

The combination of [[unit of measurement]] and the [[physical quantity]] (height) is called "[[metre]]s above mean sea level" in the [[metric system]], while in [[United States customary units|United States customary]] and [[imperial units]] it would be called "[[Foot (length)|feet]] above mean sea level".

Mean sea levels are affected by [[climate change]] and other factors and change over time. For this and other reasons, recorded measurements of elevation above sea level at a reference time in history might differ from the actual elevation of a given location over sea level at a given moment.

== Uses ==
Metres above sea level is the standard measurement of the elevation or altitude of:
* [[Geographic location]]s such as [[town]]s, [[mountain]]s and other [[landmark]]s.
* The top of [[building]]s and other [[nonbuilding structure|structure]]s.
* Flying objects such as [[airplane]]s or [[helicopters]].

== How it is determined ==
The elevation or altitude in metres above sea level of a location, object, or point can be determined in a number of ways. The most common include:
* [[Satellite navigation|Global Navigation Satellite System]] (like GPS), where a receiver [[Multilateration|determines a location]] from [[pseudorange]]s to multiple [[satellite]]s. A [[geoid]] is needed to convert the 3D position to sea-level elevation.
* [[Altimeter]], that measures [[atmospheric pressure]], which decreases as altitude increases. As atmospheric pressure changes with the weather too, a recent local measure of the pressure at a known altitude is needed to calibrate the altimeter.
* [[Stereoscopy]] in [[aerial photography]].
* Aerial [[lidar]] and [[satellite laser altimetry]].
* Aerial or satellite [[radar altimeter|radar altimetry]].
* [[Surveying]], especially [[levelling]].

Accurate measurement of historical mean sea levels is complex. Land mass [[subsidence]] (as occurs naturally in some regions) can give the appearance of [[sea level rise|rising sea levels]]. Conversely, markings on land masses that are uplifted due to geological processes can suggest a lowering of mean sea level.

== Abbreviations ==
Often, just the abbreviation MSL is used, e.g. Mount Everest (8848 m MSL), or the reference height is omitted completely, e.g. Mount Everest (8848 m).

Metres above mean sea level is commonly abbreviated mamsl or MAMSL, based on the abbreviation AMSL for "above mean sea level".{{cn|date=October 2021}}
Other abbreviations are m.a.s.l.<ref name="BC">{{cite journal|last=Ricardo Bressani|first=Ricardo|author2=Carlos Chon|year=1996|title=Effects of altitude above sea level on the cooking time and nutritional value of common beans|journal= Plant Foods for Human Nutrition|volume=49|issue=1|pages=53–61|doi=10.1007/BF01092522|pmid=9139304|s2cid=8408337}}</ref> and MASL for "metres above sea level".

== See also ==
* [[Depth below seafloor]]
* [[Geoid]]
* [[Height above average terrain]]
* [[Height above ground level]]
* [[List of places on land with elevations below sea level]]
* [[Vertical metre]]

== References ==
{{reflist}}

[[Category:Geography terminology]]
[[Category:Geodesy]]
[[Category:Topography]]
[[Category:Altitudes in aviation]]
[[Category:Vertical position]]
[[Category:Zero-level elevation points]]

Height above sea level - Revision history

ImportMaster at 20:17, 31 January 2022