Geodetic Journey

The geoid is the fundamental reference surface for heights both on land and at sea.

The geoid is defined as the surface of equal gravity potential and would coincide with the mean sea surface if the oceans were at rest with no tides or ocean circulation.

The geoid is normally determined by combining measured gravity data (on land, sea and in the air) with global models of the earth gravity potential and digital terrain models. The global geopotential models are derived by combining terrestrial observations with data measured by dedicated satellites.

 

The ongoing GRACE mission (USA and Germany) and the upcoming ESA satellite GOCE are two particularly important such satellites. GRACE has and continue to contribute in the determination of the time varying part of the geoid while GOCE will lead to significant improvements in our knowledge of the geoid on spacial scales down to 100km.

 

 

Within the last 10 years an improved knowledge of the geoid has revolutionized height determination on land by GNSS satellites, allowing heights to be determined with an accuracy of better than 2 cm in several countires. For marine areas a similar improvement is expected to take place giving oceanographers access to valuable information on ocean circulation from satellite altimetry.