Height above mean sea level

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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. Climate change and other forces can cause sea levels and elevations to vary over time. [1]

Contents

Uses

Elevation or altitude above sea level is a standard measurement for:

Units and abbreviations

Elevation or altitude is generally expressed as "metres above mean sea level" in the metric system, or "feet above mean sea level" in United States customary and imperial units. Common abbreviations in English are:

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

Altimetry is the measurement of altitude or elevation above sea level. Common techniques are: [8] [9]

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. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Altimeter</span> Instrument used to determine the height of an object above a certain point

An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water.

Atmospheric pressure, also known as air pressure or barometric pressure, is the pressure within the atmosphere of Earth. The standard atmosphere is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.

<span class="mw-page-title-main">Barometer</span> Scientific instrument used to measure atmospheric pressure

A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries.

Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context. Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.

<span class="mw-page-title-main">Sea level</span> Geographical reference point from which various heights are measured

Mean sea level is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datum – a standardised geodetic datum – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead a long-term average of tide gauge readings at a particular reference location.

Geopotential height or geopotential altitude is a vertical coordinate referenced to Earth's mean sea level that represents the work involved in lifting one unit of mass over one unit of length through a hypothetical space in which the acceleration of gravity is assumed constant. In SI units, a geopotential height difference of one meter implies the vertical transport of a parcel of one kilogram; adopting the standard gravity value, it corresponds to a constant work or potential energy difference of 9.80665 joules.

<span class="mw-page-title-main">Height</span> Measure of vertical distance

Height is measure of vertical distance, either vertical extent or vertical position . For example, "The height of that building is 50 m" or "The height of an airplane in-flight is about 10,000 m". For example, "Shaq O’Neal is 7 foot 1 inches in vertical height."

<span class="mw-page-title-main">Flight level</span> Measure in aviation

In aviation and aviation meteorology, a flight level (FL) is an aircraft's altitude at standard air pressure, expressed in hundreds of feet. The air pressure is computed assuming an International Standard Atmosphere pressure of 1013.25 hPa (29.92 inHg) at sea level, and therefore is not necessarily the same as the aircraft's actual altitude, either above sea level or above ground level.

Given an atmospheric pressure measurement, the pressure altitude is the imputed altitude that the International Standard Atmosphere (ISA) model predicts to have the same pressure as the observed value.

<span class="mw-page-title-main">Jason-1</span> Satellite oceanography mission

Jason-1 was a satellite altimeter oceanography mission. It sought to monitor global ocean circulation, study the ties between the ocean and the atmosphere, improve global climate forecasts and predictions, and monitor events such as El Niño and ocean eddies. Jason-1 was launched in 2001 and it was followed by OSTM/Jason-2 in 2008, and Jason-3 in 2016 – the Jason satellite series. Jason-1 was launched alongside the TIMED spacecraft.

<span class="mw-page-title-main">Flight plan</span> Document filed by a pilot or flight dispatcher indicating the aircrafts flight path

Flight plans are documents filed by a pilot or flight dispatcher with the local Air Navigation Service Provider prior to departure which indicate the plane's planned route or flight path. Flight plan format is specified in ICAO Doc 4444. They generally include basic information such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight, the pilot's information, number of people on board, and information about the aircraft itself. In most countries, flight plans are required for flights under IFR, but may be optional for flying VFR unless crossing international borders. Flight plans are highly recommended, especially when flying over inhospitable areas such as water, as they provide a way of alerting rescuers if the flight is overdue. In the United States and Canada, when an aircraft is crossing the Air Defense Identification Zone (ADIZ), either an IFR or a special type of VFR flight plan called a DVFR flight plan must be filed. For IFR flights, flight plans are used by air traffic control to initiate tracking and routing services. For VFR flights, their only purpose is to provide needed information should search and rescue operations be required, or for use by air traffic control when flying in a "Special Flight Rules Area."

In aviation, atmospheric sciences and broadcasting, a height above ground level is a height measured with respect to the underlying ground surface. This is as opposed to height above mean sea level, height above ellipsoid, or height above average terrain. In other words, these expressions indicate where the "zero level" or "reference altitude" – the vertical datum – is located.

<span class="mw-page-title-main">Pressure altimeter</span>

Altitude can be determined based on the measurement of atmospheric pressure. The greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is a type of altimeter called a pressure altimeter or barometric altimeter. A pressure altimeter is the altimeter found in most aircraft, and skydivers use wrist-mounted versions for similar purposes. Hikers and mountain climbers use wrist-mounted or hand-held altimeters, in addition to other navigational tools such as a map, magnetic compass, or GPS receiver.

<span class="mw-page-title-main">OSTM/Jason-2</span> International Earth observation satellite mission

OSTM/Jason-2, or Ocean Surface Topography Mission/Jason-2 satellite, was an international Earth observation satellite altimeter joint mission for sea surface height measurements between NASA and CNES. It was the third satellite in a series started in 1992 by the NASA/CNES TOPEX/Poseidon mission and continued by the NASA/CNES Jason-1 mission launched in 2001.

<span class="mw-page-title-main">Vertical datum</span> Reference surface for vertical positions

In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum, is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features and altitudes of satellite orbits and in aviation. In planetary science, vertical datums are also known as zero-elevation surface or zero-level reference.

<span class="mw-page-title-main">Ocean surface topography</span> Shape of the ocean surface relative to the geoid

Ocean surface topography or sea surface topography, also called ocean dynamic topography, are highs and lows on the ocean surface, similar to the hills and valleys of Earth's land surface depicted on a topographic map. These variations are expressed in terms of average sea surface height (SSH) relative to Earth's geoid. The main purpose of measuring ocean surface topography is to understand the large-scale ocean circulation.

<span class="mw-page-title-main">SARAL</span> Indian Earth observation satellite

SARAL is a cooperative altimetry technology mission of Indian Space Research Organisation (ISRO) and Centre National d'Études Spatiales (CNES). SARAL performs altimetric measurements designed to study ocean circulation and sea surface elevation.

Altimeter setting is the value of the atmospheric pressure used to adjust the scale of a pressure altimeter so that it indicates the height of an aircraft above a known reference surface. This reference can be the mean sea level pressure (QNH), the pressure at a nearby surface airport (QFE), or the "standard pressure level" of 1,013.25 hectopascals which gives pressure altitude and is used to maintain one of the standard flight levels.

Vertical position or vertical location is a position along a vertical direction above or below a given vertical datum . Vertical distance or vertical separation is the distance between two vertical positions. Many vertical coordinates exist for expressing vertical position: depth, height, altitude, elevation, etc. Points lying on an equigeopotential surface are said to be on the same vertical level, as in a water level.

This is a glossary of acronyms, initialisms and terms used for gliding and soaring. This is a specialized subset of broader aviation, aerospace, and aeronautical terminology. Additional definitions can be found in the FAA Glider Flying Handbook.

References

  1. "Sea Level: Frequently Asked Questions and Answers" Liverpool, UK: National Oceanography Centre. Retrieved 31 January 2024.
  2. "Altitude, Flight Level and Height". SKYbrary Aviation Safety. Retrieved 31 January 2024.
  3. "TOWAIR Determination". Federal Communications Commission. Retrieved 3 February 2024. Site Elevation (AMSL) – The elevation of the site above mean sea level (AMSL).
  4. "General Concepts". Los Angeles Air Route Traffic Control Center. Retrieved 6 April 2024. Sometimes, you will still see the abbreviation 'ASL' used as well; it stands for 'Above Sea Level'.
  5. 1 2 3 Jaramillo, Camilo; et al. (November–December 2020). "2020 ACVIM Forum On Demand Research Abstract Program: Abstract E45". Journal of Veterinary Internal Medicine. 34 (6): 2967. doi:10.1111/jvim.15904. PMC   7968404 . PMID   33037851. The horses lived at five different altitudes: 0 masl (n=23), 1000 mamsl (3280 famsl, n=25)...
  6. 1 2 Negrini, Robert M.; et al. (July 2006). "The Rambla highstand shoreline and the Holocene lake-level history of Tulare Lake, California, USA". Quaternary Science Reviews. 25 (13): 1599–1618. doi:10.1016/j.quascirev.2005.11.014. elevations from 210 fasl (64 masl) to 230 fasl (70 masl) on the Kettleman City 7.5' USGS topographic map
  7. 1 2 Moore, G. W. K.; et al. (November 2011). "Global Warming, El Niño, and High-Impact Storms at Extreme Altitude: Historical Trends and Consequences for Mountaineers". Journal of Applied Meteorology and Climatology. 50 (11): 2197–2209. JSTOR   26175013. Base Camp, 5029 m MSL ... 8570 m without the use of supplementary oxygen, an altitude record
  8. Florinsky, Igor V. (2016). "Chapter 3: Digital Elevation Models". Digital Terrain Analysis in Soil Science and Geology (2nd ed.). Academic Press. pp. 77–108. doi:10.1016/B978-0-12-804632-6.00003-1. ISBN   978-0128046326.
  9. "Introduction to Altimeters". UAV Navigation. Retrieved 20 April 2024.
  10. Church, J. A.; Clark, P. U. (2013). "Chapter 13: Sea Level Change" (PDF). Climate Change 2013: The Physical Science Basis. Cambridge University Press. pp. 1137–1216. Retrieved 20 April 2024.