SUMMARY
The rapid adoption of the GNSS (Global Navigation Satellite System) technology in our modern daily life brings the opportunity to investigate its applicability to areas beyond positioning, navigation and timing, such as meteorology. Due to its high accuracy performance, GNSS (PPP) Precise Point Positioning has become an attractive tool to retrieve the precipitable water vapor (PWV) from the atmosphere. Apart of the GNSS observations, PPP PWV retrieval also requires surface pressure and temperature measurements to calculate precisely the wet part of the tropospheric delay and convert it to PWV. This research reports on the atmospheric water estimation using GNSS PPP method. GNSS observations from CUSV IGS tracking station are combined with IGS precise data in order to obtain the best PPP estimates. Forward and backward solutions are combined using a weighted normalized approach. In addition, observation data from two meteorological stations is used in PWV estimation. The numerical analysis covered the entire year of 2016. Our analyses show that PPP combined solutions are in very good agreement with IGS official products in terms of coordinates and zenith tropospheric delays. In addition, PPP PWV estimates display seasonal and temporal variation in the water content of the atmosphere. The PWV values over 65 mm were found to be from May to November, whereas they were on average 20% lower for the other months of the year. Furthermore, PWV estimates were found to be correlated with local rainfall events recorded at the meteorological stations. Our research concludes that GNSS data processing using PPP method provides high accuracy solution that may be used for retrieving reliably information about the water content in the atmosphere.