| 31. | The reference surface for orthometric heights is the geoid, an equipotential surface approximating mean sea level.
|
| 32. | The deviations of the geoid from the first order spheroid are on the order of ?100m.
|
| 33. | Dynamic topography is the reason why the geoid is high over regions of low-density mantle.
|
| 34. | Ocean surface topography is specifically the distance between the height of the ocean surface from the geoid.
|
| 35. | Sea level can also be measured by satellites using radar altimetry, contributing to a more accurate geoid.
|
| 36. | Currently, WGS 84 uses the EGM96 ( Earth Gravitational Model 1996 ) geoid, revised in 2004.
|
| 37. | It is then possible to compute the geoid height by subtracting the measured altitude from the ellipsoidal height.
|
| 38. | Spatial variations in gravity exert influence on the ocean surface and thereby cause spatial structure in the geoid.
|
| 39. | They are used in gravity surveys over large areas for establishing the figure of the geoid over these areas.
|
| 40. | This terminology is also used for such approximately spheroidal astronomical bodies as the planet Earth ( see geoid ).
|
