Analysis of the EUREF-89 GPS data from the SLR/VLBI sites

In May 1989, the IAG Subcommission for the European Reference Frame organized a GPS measurement campaign, called EUREF-89, to establish a common European Reference Frame. During a 2-week period various types of GPS receivers were deployed at about 100 different locations in Europe, which included many national geodetic first order points and most of the well-known SLR and VLBI sites. In this study, the measurements from those SLR and VLBI sites, and three additional points in The Netherlands, have been analyzed adopting a fiducial network approach. In the first place, the study provided valuable experience in the use of the GIPSY software for the analysis of GPS data from large networks equipped with a mixture of receiver types. Furthermore, this analysis represents an independent check of the SLR/VLBI network, used as the reference frame for the official EUREF solution. Daily solutions of baselines up to 2500 km in length have been obtained with a repeatability of 0.5–2.0 parts in 10⁸, while the agreement with SLR results is at about the same level. The accuracy of the estimated coordinates is at a level of about 4.0 cm in the horizontal and 6.0 cm in the vertical direction. Of particular interest are the results for some baselines in Greece, which have also been measured by mobile SLR in the framework of the WEGENER/MEDLAS project. The GPS results seem to confirm the trends in the baseline length changes emerging from those SLR studies.