Monitoring variations in precipitable water vapor in the mid-latitude zone using the GNSS radio occultation technique

Analyzing changes in the Earth's climate system is made possible by long-term observations of the temperature structure and water vapor concentration in the troposphere and stratosphere. In recent years, the Global Navigation Satellite System-Radio Occultation (GNSS-RO) technique has been widely preferred in meteorology and climate change research. PWV calculation with GNSS-RO technique is a method that has recently started to be used in climatic water vapor analysis and there is no study in this field in our country yet. In this study, for the first time in Türkiye, which is located in the mid-latitude zone, and in Italy (Trapani/Birgi), a software that estimates PWV using GNSS-RO technique has been developed. For this purpose, GNSS-RO atmospheric profiles and PWV values were analyzed in the regions where radiosonde stations are located and comparisons were made with IGRA profiles and ECMWF ERA5 products. The relationship between GNSS-RO, Radiosonde, and ERA5 PWV was analyzed with absolute error, squared mean error, relative error, regression, pearson correlation and R2 coefficient. In addition, GNSS-RO PWV values were compared with PWV values produced during periods of extreme hydrological disasters in the Black Sea region. Generally, a good agreement is observed in results.