The processing of single differenced GNSS data with VLBI software

Abstract

Space geodetic techniques such as Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) are used for the determination of celestial and terrestrial reference frames and Earth orientation parameters. It is potentially valuable to combine the observations from the different techniques to fully exploit the strengths and unique characteristics of the techniques. Today, discrepancies of locally measured ties between reference points of two techniques and the space geodesy results are a potential issue in the determination of reference frames. To improve the link between the techniques, tests are under way to observe GNSS signals with VLBI radio telescopes directly, and to observe GNSS signals in GNSS antennas with subsequent processing in the VLBI system (“GNSS-VLBI Hybrid System”) including VLBI correlation. In both cases, the GNSS data type is the difference in travel time from the satellite to two ground stations. However, it is still difficult to acquire those observations and thus we apply post-processed phase measurements from a precise point positioning (PPP) solution with the c5++ software to build those difference values which are then used in the Vienna VLBI Software (VieVS). We take seven GNSS sites, exclusively Global Positioning System (GPS) in this study, colocated with CONT11 VLBI sites to validate the models in VieVS for single differenced GNSS data, and estimate geodetic parameters. We find root mean square values of postfit residuals for the VLBI-like observations of about 3.3 cm, compared to less than 2.0 cm fromthe GNSS PPP solution. At this stage, we do also find degradation in station coordinate repeatabilities (by a factor of 2 to 8), which is related to the systematic residuals.