Abstract
Abstract. Currently, GPS campaign measurements (i.e. repeated GPS measurements) are used frequently in order to determine geophysical phenomena such as tectonic motion, fault zones, landslides, and volcanoes. The coordinates of a new point installed in a study area are usually found either by using relative point positioning or precise point positioning (PPP). Employing observation sessions shorter than 24 h might still be a necessity at times. When observation duration is shorter, the accuracy of coordinates are degraded and also the accuracy of point velocities are affected. The accuracies of the geodetic site velocities from a global network of the International GNSS Service (IGS) stations were previously investigated using only PPP. In this study, we extend that study in which site velocities will also be assessed including fundamental relative positioning. PPP derived results will also be evaluated to see the effect of JPL reprocessed products and single receiver ambiguity resolution. IGS is a good data source for simulation studies and hence globally distributed 18 continuously operating IGS stations were chosen to create synthetic GPS campaigns. GPS data were processed comparatively using GAMIT/GLOBK v10.6 and GIPSY/OASIS II v6.3. The data of synthetic campaign GPS time series were processed using a regression model accounting for the linear and seasonal variation of the ground motion. Once accepting the velocities derived from 24 h sessions as the truth, the results from sub-sessions were compared with the results of 24 h and hypothesis testing was applied for the significance of the differences. The major outcome of this study is that at global scales (i.e. over long distances) with short observation sessions, the fundamental relative positioning produces similar results to PPP. The reliability of the velocity estimation for horizontal components has now been improved to about 85 % on the average for observation durations of 12 h.