Towards A Combination Of Space-Geodetic Measurements

The International Terrestrial Reference Frame (ITRF), the Earth Orientation Parameter (EOP) time series, and the International Celestial Reference Frame are obtained separately and may thus present inconsistencies. To solve this problem, a first step has been made with the latest ITRF realization (ITRF2005), which has been computed, for the first time, with consistent EOP time series. Another approach to better understand this issue is to directly estimate, in the same process, station positions and EOP time series, from all the space-geodetic measurements.In the framework of the French Groupe de Recherche de Geodesie Spatiale (GRGS) activities, this latter approach has been studied for several years. For this purpose, the observations of VLBI, SLR, GPS, and DORIS techniques are combined using the same models and software for all the individual data processing.In this paper, we study methodological issues regarding the definition and the consistency of the weekly combined terrestrial frames.