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Height above mean sea level is a measure of a location's vertical distance (height, elevation or altitude) in reference to a vertical datum based on a historic 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.
Originally known as Sea Level Datum of 1929, NGVD 29 was determined and published by the United States Coast and Geodetic Survey [2] and used to measure the elevation of a point above and depression below mean sea level (MSL).
Vertical references in Europe View from Newlyn harbour showing the lighthouse and Newlyn Tidal Observatory to its right, both painted red and white. An ordnance datum (OD) is a vertical datum used by an ordnance survey as the basis for deriving altitudes on maps. A spot height may be expressed as above ordnance datum (AOD).
NAVD 88 was established in 1991 by the minimum-constraint adjustment of geodetic leveling observations in Canada, the United States, and Mexico.It held fixed the height of the primary tide gauge benchmark, referenced to the International Great Lakes Datum of 1985 local mean sea level (MSL) height value, at Rimouski, Quebec, Canada.
The orthometric height (symbol H) is the vertical distance along the plumb line from a point of interest to a reference surface known as the geoid, the vertical datum that approximates mean sea level.
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).
Middlebury State Airport covers an area of 156 acres (63 ha) at an elevation of 490 feet (149 m) above mean sea level.It has one runway designated 01/19 with an asphalt surface measuring 3,206 by 60 feet (977 x 18 m). [1]
Stephen A. Bean Municipal Airport covers an area of 125 acres (51 ha) at an elevation of 1,825 feet (556 m) above mean sea level.It has one runway designated 14/32 with an asphalt surface measuring 3,201 by 75 feet (976 x 23 m).