Problems in the Definition of Vertical Reference Frames

Abstract

Present and future satellite-borne gravity field missions will have a major impact on the unification of regional height systems into a consistent global vertical reference frame. On the background of the high precision and quality of the expected data the scientific concepts of vertical reference frames have to be discussed, before a global frame will be implemented or before international standards and conventions can be fixed.This paper addresses some major theoretical problems in the definition of vertical reference frames such as difficulties due to the time-dependence of the gravity field and its level surfaces, problems in assigning a geoidal potential value W0, and the consistent treatment of the permanent tidal effect. Examples from the European Vertical Reference Frame 2000 (EVRF 2000) and the draft of the IERS conventions 2000 prove that these inconsistencies are inherent in several branches of Geodesy and must be taken care of in the practical work involving height systems. Emphasis is given to the formulation of open problems rather than to the presentation of solutions.KeywordsVertical reference framesgravity fieldgeoidpermanent tidal effects