Contribution of Individual Space Techniques to the Realization of Vertical Reference Systems

The most precise space geodetic techniques for the realization of global terrestrial reference systems are VLBI, SLR and GPS. We focus on the contribution of these techniques to the determination of the vertical component. We discuss the strengths and weaknesses of each of the technique regarding the height determination as well as the effect of systematic errors. The quality of the ITRF (especially with respect to the vertical component) is assessed. Finally VLBI, SLR and GPS time series of position estimates are used to discuss the time—dependent stability of the solutions.