Dynamic height is a way of specifying the

vertical position Vertical position or vertical location, also known as vertical level or simply level, is a position along a vertical direction above or below a given vertical datum (reference level). Vertical distance or vertical separation is the distance betwee ...

of a point above a

vertical datum 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 (terrain, bathymetry, water level, and built stru ...

; it is an alternative for

orthometric height The orthometric height is the vertical distance ''H'' along the plumb line from a point of interest to a reference surface known as the ''geoid'', the vertical datum that approximates mean sea level. Orthometric height is one of the scientific fo ...

normal height Normal heights is a type of height above sea level introduced by Mikhail Molodenskii. The normal height H^* (or H^N) of a point is computed as the ratio of a point's geopotential number (i.e. its geopotential difference with that of sea level), by t ...

. It can be computed dividing the location's

geopotential number 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 this potential, without the nega ...

by the

normal gravity In geodesy and geophysics, theoretical gravity or normal gravity is an approximation of the true gravity on Earth's surface by means of a mathematical model representing Earth. The most common model of a smoothed Earth is a rotating Earth ellipsoi ...

at 45 degree latitude (a constant). Dynamic height is constant if one follows the same gravity potential as one moves from place to place. Because of variations in gravity, surfaces having a constant difference in dynamic height may be closer or further apart in various places. Dynamic heights are usually chosen so that zero corresponds to the

geoid The geoid () is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended ...

. Dynamic height is the most appropriate height measure when working with the level of water over a large geographic area; it is used by the Great Lakes Datum in the US and Canada. When

differential leveling Levelling or leveling (American English; see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartog ...

is done, the path corresponds closely to following a value of dynamic height horizontally, but not to orthometric height for vertical changes measured on the leveling rod. Thus small corrections must be applied to field measurements to obtain either the dynamic height or the

usually used in engineering. US National Geodetic Survey data sheets give both dynamic and orthometric values.

References

Geodesy Vertical position {{geodesy-stub

See also

References