Height above mean sea level
(Redirected from
Metres above sea level
)Height above mean sea level is a measure of a location's
mean sea level. In geodesy, it is formalized as orthometric height. The zero level varies in different countries due to different reference points and historic measurement periods. Climate change and other forces can cause sea levels and elevations to vary over time.[1]
Uses
Elevation or altitude above sea level is a standard measurement for:
- Geographic locations such as towns, mountains and other landmarks.
- The top of structures.
- Mining infrastructure, particularly underground.
- Flying objects such as helicopters below a Transition Altitude defined by local regulations.[2]
Units and abbreviations
Elevation or altitude is generally expressed as "
feet above mean sea level" in United States customary and imperial units
. Common abbreviations in English are:
- AMSL – above mean sea level[3]
- ASL – above sea level[4]
- FAMSL – feet above mean sea level[5]
- FASL – feet above sea level[6]
- MAMSL – metres above mean sea level[5]
- MASL – metres above sea level[5][6]
- MSL – mean sea level[7]
For elevations or altitudes, often just the abbreviation MSL is used, e.g., Mount Everest (8849 m MSL), or the reference to sea level is omitted completely, e.g., Mount Everest (8849 m).[7]
Methods of measurement
 | This section needs additional citations for verification. (February 2024) |
Elevation or altitude above sea level is most commonly measured by:
- is needed to convert the 3D position to sea-level elevation.
- Altimeter measuring atmospheric pressure, which decreases as altitude increases. Since atmospheric pressure varies 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 satellite laser altimetry.
- Aerial or satellite 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 rising sea levels. Conversely, markings on land masses that are uplifted (due to geological processes) can suggest a relative lowering of mean sea level.
See also
- Depth below seafloor
- Height above average terrain
- Height above ground level
- List of places on land with elevations below sea level
References
- ^ "Sea Level: Frequently Asked Questions and Answers" Liverpool, UK: National Oceanography Centre. Retrieved 31 January 2024.
- ^ "Altitude, Flight Level and Height". SKYbrary Aviation Safety. Retrieved 31 January 2024.
- ^ "TOWAIR Determination". Federal Communications Commission. Retrieved 3 February 2024.
Site Elevation (AMSL) – The elevation of the site above mean sea level (AMSL).
- ^ "General Concepts". Los Angeles ARTCC. Retrieved 6 April 2024.
- ^ PMID 33037851.
The horses lived at five different altitudes: 0 masl (n=23), 1000 mamsl (3280 famsl, n=25)...
- ^ .
elevations from 210 fasl (64 masl) to 230 fasl (70 masl) on the Kettleman City 7.5' USGS topographic map
- ^ JSTOR 26175013.
Base Camp, 5029 m MSL ... 8570 m without the use of supplementary oxygen, an altitude record
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