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Standard sea-level conditions (SSL), [1] also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations.The term "standard sea level" is used to indicate that values of properties are to be taken to be the same as those standard at sea level, and is done to define values for use in general calculations.
A common and relatively straightforward mean sea-level standard is instead a long-term average of tide gauge readings at a particular reference location. [1] The term above sea level generally refers to the height above mean sea level (AMSL). The term APSL means above present sea level, comparing sea levels in the past with the level today.
A chart datum is the water level surface serving as origin of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. [1]
This is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea level for locations above or below sea level. The average pressure at mean sea level in the International Standard Atmosphere is 1,013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury.
Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. To accommodate the lowest points on Earth, the model starts at a base geopotential altitude of 610 meters (2,000 ft) below sea level, with standard temperature set at 19 °C.
The standard atmosphere (symbol: atm) is a unit of pressure defined as 101 325 Pa. It is sometimes used as a reference pressure or standard pressure . It is approximately equal to Earth 's average atmospheric pressure at sea level .
Using peer-reviewed sea level rise projections and local elevation from Climate Central’s models, the findings show compelling visuals that paint a stark contrast between the world as we know it ...
Since the Sea Level Datum of 1929 was a hybrid model, it was not a pure model of mean sea level, the geoid, or any other equipotential surface. Therefore, it was renamed the National Geodetic Vertical Datum of 1929 (NGVD 29) May 10, 1973, by the National Geodetic Survey , a part of the National Oceanic and Atmospheric Administration .