Sea level the warmer water expands. For at least the last 100 years, sea level has been rising at an average rate of about per year. Most of this rise can be attributed to the increase in temperature of the sea and the resulting slight thermal expansion of the upper of sea water. Additional contributions, as much as one-quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human uses. Pilots can estimate height above sea level with an altimeter set to a defined barometric pressure.
Normal gravity formula equator and lowest the poles. The formulas for calculating the normal gravity is based on the assumption of an imagined rotationally symmetrical ellipsoid model of the earth, the surface of which is identical to an equipotential surface. Consequently this formula depends only on the geographical latitude and the elevation of geographical location. For the normal gravity formula_1 of the sea level ellipsoid, i.e. elevation h = 0, this formula by Somigliana (1929) applies (after Carlo Somigliana (1860–1955)): with Due to numerical issues, the formula is simplified into this: with For the Geodetic Reference System 1980 (GRS 80) the parameters are