Reference height

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In geosciences and technology, the reference altitude is understood to be the altitude above sea level to which precise altitude measurements from a state or state survey refer. Landlocked states define derived geodetic datum points (fixed points "zero order") on their national territory with their exact sea level. They mostly also serve as points of the gravity network .

In coastal states, the original reference point is usually a mareographer (or a system of gauges ) on the nearest sea coast. From this reference level, the respective national survey - mostly for the first time in the 18th or 19th century - carried out a network-like precision leveling over the national territory. The results of such height networks were / are marketed along the measuring lines as a large number of derived height control points  (HFP) in stable buildings ( tower or leveling bolts) or in natural rock and secured by further control points in the vicinity, sometimes also as assigned height of measurement points in their data file specified. They are available to technicians at a distance of a few 100 meters to kilometers. Because of their precise reference to a national system, these altitude points can also be viewed as indirect or local reference altitude.

In the navigation

In addition to geodesy, the term "reference height" is mainly used in navigation :

In meteorology

The Meteorology refers calculated or measured data often to a certain height - u. a. in the humidity and in models of the wind field, especially the high-altitude winds . In view of the strong upward increase in wind speeds (see logarithmic wind profile ), the current wind at a certain altitude is related to that at the "reference altitude" in order to put the wind formula for the vertical increase on a suitable empirical basis.