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Geopotential height differs from geometric height (as given by a tape measure) because Earth's gravity is not constant, varying markedly with altitude and latitude; thus, a 1-m geopotential height difference implies a different vertical distance in physical space: "the unit-mass must be lifted higher at the equator than at the pole, if the same ...
Geopotential is the potential of the Earth's gravity field. For convenience it is often defined as the negative of the potential energy per unit mass , so that the gravity vector is obtained as the gradient of the geopotential, without the negation.
EGM96: The NASA GSFC and NIMA Joint Geopotential Model; Earth Gravitational Model 2008 (EGM2008) GeographicLib provides a utility GeoidEval (with source code) to evaluate the geoid height for the EGM84, EGM96, and EGM2008 Earth gravity models. Here is an online version of GeoidEval.
Certain vertical coordinates are not based on length, for example, geopotential numbers have units of m 2 /s 2. Normalization by a constant nominal gravity value (units of m/s 2) yields units of metre, as in geopotential height (based on standard gravity) or dynamic height (based on normal gravity at 45 degrees latitude).
The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface. Elevation histogram of the Earth's surface
In geophysics and physical geodesy, a geopotential model is the theoretical analysis of measuring and calculating the effects of Earth's gravitational field (the geopotential). The Earth is not exactly spherical, mainly because of its rotation around the polar axis that makes its shape slightly oblate.
Dynamic height is a way of specifying the vertical position of a point above a vertical datum; it is an alternative for orthometric height or normal height.It can be computed by dividing the location's geopotential number by the normal gravity at 45 degree latitude and zero height, a constant value (9.806199203 m/s 2). [1]
First, the distinction is geopotential height as a function of pressure (isobaric coordinates) instead of pressure as a function of height (geometric coordinates) - geopotential height and geometric height are equivalent for virtually any atmospheric phenomena in the troposphere (the two differ only due to variations of g with height).