above mean sea level

Information about above mean sea level

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The term above mean sea level (AMSL) refers to the elevation (on the ground) or altitude (in the air) of any object, relative to the average sea level datum. AMSL is used extensively in radio (both in broadcasting and other telecommunications uses) by engineers to determine the coverage area a station will be able to reach. It is also used in aviation, all heights are recorded and reported with respect to AMSL (though also see flight level), and in the atmospheric sciences.

Definition

The concept of a "mean sea level" is in itself rather artificial, because it is not possible to determine a figure for mean sea level for the entire planet, and it varies quite a lot even on a much smaller scale. This is because the sea is in constant motion, affected by the high and low pressure zones above it, the tides, local gravitational differences, and so forth. The best one can do is to pick a spot and calculate the mean sea level at that point and use it as a datum. For example, the Ordnance Survey uses a height datum based on the measurements of mean sea level at a particular gauge at Newlyn, Cornwall from 1915 to 1921 [1] for their maps of Great Britain, and this datum is actually some 80cm different from the mean sea level reading obtained on the other side of the country. An alternative is to base height measurements on an ellipsoid of the entire earth, which is what systems such as GPS do. In aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define mean sea level. Another alternative is to use a geoid based datum such as NAVD88.

Usage

When referring to geographic features such as mountains on a topographic map, variations in elevation are shown by contour lines. The elevation of a mountain denotes the highest point or summit and is typically illustrated as a small circle on a topo map with the AMSL height shown in either meters or feet or both.

The height above average terrain (HAAT) for a station is determined from topographic maps by averaging the elevation AMSL at points along several radials or radii. This is subtracted from the elevation AMSL of the antenna, including both the tower itself and the ground it is on, to determine the difference. Negative numbers for HAAT sometimes result from this when the station or airport is in a valley, which is significantly lower AMSL than the surrounding mountains. In the rare case that a location is below sea level, AMSL itself is a negative number. For one such case see Schiphol Airport.

AMSL is also important to engineers in high-elevation areas because some equipment is not designed with enough airflow for sufficient cooling in the thin air, which can cause overheating, damage, and failure of the electronic components within a transmitter.

See also

References

elevation of a geographic location is its height above a fixed reference point, often the mean sea level. Elevation, or geometric height, is mainly used when referring to points on the Earth's surface, while altitude or geopotential height
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For other uses see Altitude (disambiguation)


Altitude is the elevation of an object from a known level or datum (plural: data). Common data are mean sea level and the surface of the WGS-84 geoid, used by GPS.
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Air or Earth's atmosphere is a layer of gases surrounding the planet Earth.

Air may also refer to:
  • Air (1977 video game), an air combat based mainframe computer game
  • Air (band), a French electronic music duo

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In mathematics, an average, or central tendency of a data set refers to a measure of the "middle" or "expected" value of the data set. There are many different descriptive statistics that can be chosen as a measurement of the central tendency of the data items.
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This article or section relies largely or entirely upon a .
Please help [ improve this article] by introducing appropriate of additional sources. ()
This article has been tagged since December 2006.
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This article describes a concept from surveying and geodesy. Datum is also the last known position of a submarine in ASW, the singular form of data, and a city in ancient Macedonia, probably on the site of the modern Kavala.

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Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space.
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Broadcasting is the distribution of audio and/or video signals which transmit programs to an audience. The audience may be the general public or a relatively large sub-audience, such as children or young adults.
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Telecommunication is the transmission of signals over a distance for the purpose of communication. In modern times, this process typically involves the sending of electromagnetic waves by electronic transmitters, but in earlier times telecommunication may have involved the use of
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engineer is someone who is trained or professionally engaged in a branch of engineering.[1] Engineers use technology, mathematics, and scientific knowledge to solve practical problems.
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Coverage may refer to:
  • Insurance coverage, the amount and extent of risk covered by an insurer
  • Coverage (telecommunication), a measure of cell phone connectivity
  • Radio frequency
  • News ("press coverage", "media coverage")

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Area is a physical quantity expressing the size of a part of a surface. The term Surface area is the summation of the areas of the exposed sides of an object.

Units

Units for measuring surface area include:
square metre = SI derived unit

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Aviation refers to all activities involving the operation of heavier-than-air aircraft, machines designed for atmospheric flight. The term also describes the organizations and regulatory bodies as well as the personnel related with the operation of aircraft and the industries
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In aviation, a Flight Level (FL) is a standard nominal altitude of an aircraft, referenced to a world-wide fixed pressure datum of 1013.25 mbar or the equivalent setting, 29.921 inHg (the average sea-level pressure).
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Atmospheric sciences is an umbrella term for the study of the atmosphere, its processes, the effects other systems have on the atmosphere, and the effects of the atmosphere on these other systems.
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This article describes a concept from surveying and geodesy. Datum is also the last known position of a submarine in ASW, the singular form of data, and a city in ancient Macedonia, probably on the site of the modern Kavala.

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Ordnance Survey (OS) is an executive agency of the United Kingdom government. It is the national mapping agency for Great Britain,[1] and one of the world's largest producers of maps.
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Newlyn
Cornish - Lulynn

Newlyn ()
|240px|Newlyn (

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Cornwall
Kernow

(Flag)
Motto: Onen hag oll
(Cornish: One and all)

Geography
Status Ceremonial & (smaller) Non-metropolitan county
Region South West England
Area
- Total
- Admin.
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ellipsoid is a type of quadric surface that is a higher dimensional analogue of an ellipse. The equation of a standard ellipsoid body in an x-y-z Cartesian coordinate system is
where a and b
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Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its
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The World Geodetic System defines a reference frame for the earth, for use in geodesy and navigation. The latest revision is WGS 84 dating from 1984 (last revised in 2004), which will be valid up to about 2010.
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geoid is that equipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were to be extended through the continents (such as with very narrow canals). According to C.F.
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This article describes a concept from surveying and geodesy. Datum is also the last known position of a submarine in ASW, the singular form of data, and a city in ancient Macedonia, probably on the site of the modern Kavala.

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Geography - (from the Greek words Geo (γη) or Gaea (γαία), both meaning "Earth", and graphein (γράφειν) meaning "to describe" or "to write"
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mountain is a landform that extends above the surrounding terrain in a limited area. A mountain is generally steeper than a hill, but there is no universally accepted standard definition for the height of a mountain or a hill although a mountain usually has an identifiable
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topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods.
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contour map (topographic map) uses contour lines (often just called a "contour") to join points of equal elevation (height) and thus show valleys and hills, and the steepness of slopes.
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Height is the measurement of vertical distance, but has two meanings in common use. It can either indicate how "tall" something is, or how "high up" it is. For example one could say "That is a tall building", or "That airplane is high up in the sky".
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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