Guergana Guerova is an associate professor in the Department of Meteorology and Geophysics of the Sofia University "St. Kliment Ohridski, Sofia, Bulgaria. She received an MSc in meteorology from the Sofia University (1995) and PhD in applied physics from the University of Bern (2003). She is Marie Curie IRG Fellow (2011–2014), vice chair of COST Action ES1206 GNSS4SWEC (2013–2017), and team leader of Interreg BERTISS project (2017–2019). Her research interests cover monitoring short- and long-term variation in GNSS-derived water vapor, in particular for studying fog, intense precipitation, hail storms, and heat waves. She is recognized internationally in the field of GNSS meteorology and numerical modelling of the atmosphere.Tzvetan Simeonov is a research scientist at the GRUAN Lead Center at Deutscher Wetterdienst. He is a former student of Guergana Guerova, graduating with honors from his MSc in GNSS meteorology at the Sofia University "St. Kliment Ohridski (2013). After earning his master's degree, he worked in the German Research Centre for Geosciences (GFZ Potsdam) on GNSS Reflectometry (2016–2019), where he defended his PhD thesis on observations of the hydrological cycle with ground-based GNSS stations. Since 2019, he has worked on theestimation of measurement uncertainties of meteorological radiosondes with a focus on their positioning and pressure observations within the GRUAN project of the WMO.