Dynamic height (symbol
or
) is a way of specifying the
vertical position
Vertical position or vertical location is a position (mathematics), position along a vertical direction (the plumb line direction) above or below a given vertical datum (a reference level surface, such as mean sea level).
Vertical distance or vert ...
of a point above a
vertical datum; it is an alternative for
orthometric height or
normal height
Normal heights (symbol H^* or H^N; SI unit metre, m) is a type of height above sea level introduced by the Soviet scientist Mikhail Molodenskii.
The normal height of a point is defined as the quotient of a point's geopotential number ''C'' (i.e. it ...
. It can be computed (in
SI units
The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official st ...
of
metre
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
) by dividing the location's
geopotential number (symbol ''C'', in
square metre per square second
In classical mechanics, the gravitational potential is a scalar potential associating with each point in space the work (energy transferred) per unit mass that would be needed to move an object to that point from a fixed reference point in the ...
) by the
normal gravity (symbol , in
metres per square second) at 45 degree latitude and zero height, a constant value (9.806199203 m/s
2):
[
:
Dynamic heights are usually chosen so that zero corresponds to the geoid.
As dynamic height is proportional to the ]geopotential
Geopotential (symbol ''W'') is the potential of the Earth's gravity field. It has SI units of square metre per square seconds (m2/s2). For convenience it is often defined as the of the potential energy per unit mass, so that the gravity vect ...
, it remains constant over a given equigeopotential surface.
Therefore, dynamic height is the most appropriate height measure when working with the level of water (as in hydrology
Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydro ...
or oceanography
Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology.
It is an Earth science, which covers a wide range of to ...
) over a large geographic area.Earth's gravity
The gravity of Earth, denoted by , is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation).
It is a vector qu ...
, two surfaces having a constant difference in dynamic height or in geopotential do not have a constant geometric distance; for example, they are closer and further apart at the poles and at the equator, respectively.
See also
* Geopotential height, a similar quantity used in meteorology, based on a slightly different gravity value
References
Geodesy
Vertical position
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