| Summary: | The focus in this presentation is on principles for, and implementation of, long term management of geodetic reference frames under the circumstance of a deforming crust of the earth. Of special importance is the need from the users to have a reference frame where the coordinate values are stable in time. To achieve this, the deformations of the earths crust must be known. For northern Europe, these deformations are dominated by the Fennoscandian Glacial Isostatic Adjustment (GIA) process, where the maximum land uplift is at the 10 mm/yr level. A recent 3D velocity field derived from more than 4800 days (13 years) of data at more than 80 permanent GPS sites in northern Europe is first presented. The results agree with tide gauge observations and repeated levellings to the 0.5 mm/yr level. Then a geophysical GIA model has been tuned to best fit to the GPS-derived station velocities. The agreement between model and observations is at the sub-mm/yr level. For the purpose of eliminating or reducing the effects of crustal deformations in surveying applications, the GIA model has then been implemented in a transformation scheme, where new observations are translated backwards in time to the epoch of validity for the national reference frame.
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