A Discussion of Fundamental Constants in View of Geodetic Reference Systems

Abstract

Besides global terrestrial reference systems, such as ITRF (S) WGS 84, as updated in 1997, there exist a variety of continental or regional reference systems basically related to ITRF. With ongoing applications of global vertical positioning a global vertical datum becomes feasible. As systems, such as EUREF etc., are basically three-dimensional, the combination and unification of continental and regional vertical datums can now be implemented. First approaches of that kind, using tide-gauges in combination with repeat GPS-positioning as well as levelling together with satellite altimetry of different kind (TP, ERS-1/2 etc.) are affected by the temporal changes of global heights which are basically different from temporal changes in horizontal systems which are dominated by global plate tectonics in such a way that, at least, large scale behavior can be modelled by NUVEL-1A and similar systems. Moreover, in vertical systems the global geoid in terms of the geopotential W has to be incorporated. Thus an additional parameter which is not very well known globally, even though regional differences were meanwhile quite well explored, plays a significant role. Together with the geoid a Somigliana type normal field is appropriately introduced. In view of ecological and climatological aspects the mass exchange of ocean and atmosphere, its temporal variations in terms of El Nino and climatology, and a variety of dynamic aspects related to oceanic effects become relevant. In SC-3 of IAG all these aspects are presently discussed. New results have been investigated and compared with each other. In that connection the geopotential at the geoid W° plays a significant role and the accuracy of its present determination, problems associated with it, its interrelation with other global parameters and its use as a primary constant were considered. Results are presented in this paper.