![]() NGA provides grids with differences between WGS84 ellipsoid and EGM 2008 and EGM96, and works worldwideĭerived from horizontal datum and satellite measurments Traditional survey and leveling, using bench marks, and tied to tide station(s)Ĭreated from Geoid model from satellite observations with Think about how hard it is to measure sea level.ĭefinitions of height (from an old NIMA web page) The "ortho" in orthometric means correct,īecause we expect heights to be in terms of sea level even if we don't normally Positioning System (GPS) which are referenced to the ellipsoid. (3-D) datums realized through space-based systems such as Global High or low water, called tidal datums, and three-dimensional ![]() Orthometric datums, those based on tidally-derived surfaces of Satellite radarĪltimeters like Geosat and Topex/Poseidon have measured thesesĬhanges in the ocean geoid to an accuracy and precision level ofĬategories: those based on a form of Mean Sea Level (MSL), called Of ☑ m reflect ocean currents, over 10's of km. These are only about ☑0 m and occur over hundreds of km so the Smaller scale changes reflect ocean ridges and trenches, but In the mantle (fossilized plate tectonics), and the large changes occur over 1000s of The geoid variesįrom the ellipsoid by ☑00 m, primarily due to mass imbalances So there is no tendency for water to flow downhill because the The same value of gravity, directed perpendicular to the surface, This means that every location on the geoid has Very close to the geoid, a gravitational equipotential The ellipsoid, the best fitting shape of the earth. To sea level, but in practice that is difficult to measure
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |