Dynamic heights are usually chosen so that zero corresponds to the geoid.
3.
Dynamic height is constant if one follows the same gravity potential as they move from place to place.
4.
Because of variations in gravity, surfaces having a constant difference in dynamic height may be closer or further apart in various places.
5.
Thus small corrections must be applied to field measurements to obtain either the dynamic height or the orthometric height usually used in engineering.
6.
Orthometric heights are usually used in the US for engineering work, although dynamic height may be chosen for large-scale hydrological purposes.
7.
Elevation may be specified as normal height ( above a reference ellipsoid ), orthometric height, or dynamic height which have slightly different definitions.
8.
When optical leveling is done, the path corresponds closely to following a value of dynamic height horizontally, but to orthometric height for vertical changes measured on the leveling rod.
9.
Dynamic height is the most appropriate height measure when working with the level of water over a large geographic area, and is used by the Great Lakes Datum in the US and Canada.
10.
Using the larger Pacific basin as an example, the resulting dynamic height pattern consists of a trough at the equator, and ridge near 5?degrees north, a trough at 10�N, and finally a ridge closer to 20�N . From geostrophy ( the perfect balance between the mass field and velocity field ), the NECC is located between the ridge and trough at 5�N and 10�N, respectively.
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