Lesson plan
Dynamic height
Dynamic height (symbol H^\text{d} or H^\text{dyn} ) 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 (in SI units of metre) by dividing the location's geopotential number (symbol C, in square metre per square second) 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 ): : H^\text{d}=C/g_c Dynamic heights are usually chosen so that zero corresponds to the geoid. As dynamic height is proportional to the geopotential, 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 or oceanography) over a large geographic area. For example, it is used by the International Great Lakes Datum, across the US and Canada. However, because of variations in Earth's gravity, 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. When differential leveling 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.…
Article summary
Dynamic height (symbol H^\text{d} or H^\text{dyn} ) 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 (in SI units of metre) by dividing the location's geopotential number (symbol C, in square metre per square second) 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 ): : H^\text{d}=C/g_c Dynamic heights are usually chosen so that zero corresponds to the geoid. As dynamic height is proportional to the geopotential, 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 or oceanography) over a large geographic area. For example, it is used by the International Great Lakes Datum, across the US and Canada. However, because of variations in Earth's gravity, 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. When differential leveling 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.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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