Improving GNSS PPP accuracy through WVR PWV augmentation

Using 5 months of observations at a Global Navigation Satellite System (GNSS) and a Water Vapor Radiometer (WVR) collocated station at Tongji University, Shanghai, a mid-latitude coastal city in China with high level of water vapor, we analyzed the precipitable water vapor (PWV) from different sources including WVR, GNSS, Numerical Weather Prediction model (NWP) and radiosonde (RS). The highest correlation coefficient of 99.8% between GNSS PWV and WVR PWV with a linear fitting root-mean-square (RMS) error of 1 mm was obtained. The WVR observations were further applied in GNSS Precise Point Positioning (PPP) to demonstrate its benefits compared to the traditional PPP where troposphere delay was estimated. Both the Global Positioning System (GPS) and Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) observations were used, and the impact of estimating tropospheric gradients was also investigated. Experiments show that the WVR-constrained PPP improves the weekly repeatability, convergence time, and short-term precision in the vertical component for GPS + GLONASS and GPS-only PPP, in both static and kinematic cases. For the vertical component of daily static GPS + GLONASS PPP, the weekly repeatability of the daily static solutions was improved by ~ 5%; the convergence time was shortened by ~ 30–50%. The short-term static GPS + GLONASS PPP vertical precision was improved by 30–53% when the WVR PWV was used as a constraint and troposphere gradients were estimated. The kinematic GPS-only PPP solution showed 10–15% improvement in the vertical component when the WVR PWV was used as a constraint. However, the kinematic GPS + GLONASS PPP solution showed very limited improvement in the vertical precision when the WVR PWV was constrained. In general, the use of WVR PWV constraint did not improve the horizontal accuracy in either GPS-only or GPS + GLONASS PPP solutions, in either static or kinematic cases.