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Exploitation of ground-based Global Navigation Satellite Systems (GNSS) for Meteorology and Climate studies in Bulgaria/Southeast Europe

Final Report Summary - GNSS METEOROLOGY (Exploitation of ground-based Global Navigation Satellite Systems (GNSS) for Meteorology and Climate studies in Bulgaria/Southeast Europe)

The Global Navigation Satellite Systems (GNSS), a new technology that revolutionised the navigation, is becoming an accurate sensor of the most abundant greenhouse gas, namely atmospheric water vapour. As the GNSS signal travels trough the atmosphere its propagation is affected by atmospheric gases and in particular water vapour. From the GNSS signal time delay in the lower atmosphere the vertically Integrated Water Vapour (IWV) data with high temporal and spatial resolution can be derived. Application of GNSS in Meteorology is a well established research field in Europe and GNSS data from over 2,000 stations are available for model validation and assimilation in state-of-the-art models used for operational Numerical Weather Prediction (NWP) by the National Meteorologic Services. Advances in GNSS data processing is making possible to also use the GNSS data for climate science.

Application of GNSS tropospheric products for meteorology and climate studies in Bulgaria/Southeast Europe was initiated with this project. The work was conducted in close collaboration with the University of Bern, the University of Luxembourg and national partners. This project aimed at: (1) development a water vapour database and (2) use the data for meteorology and climate studies in Bulgaria/Southeast Europe.

A user friendly regional water vapour database named the Sofia University Atmospheric Data Archive (SUADA, was developed in collaboration with the Institute of Applied Physics of University of Bern. As of 1.1.2015 recorded in SUADA are: 1) over 30 000 000 GNSS Zenith Total Delay (ZTD) for 107 stations, 2) Integrated Water Vapour (IWV) from GNSS (245 100 for 32 stations), radiosonde (6 376 for one station), NWP model (175 000 for 39 grid points) and climate model (23 352 for two grid points). In addition, over 200 000 individual records of Planetary Boundary Layer height from ceilometer instrument are archived. The SUADA data is accessible via web portal ( At present the SUADA web portal has 15 registered users: 9 from Bulgaria and 6 international from Algeria, Germany, Poland (2), Romania and Turkey.

The use of SUADA data for meteorology and climatology studies covered both the short- and long-term variation of IWV derived from GNSS over Bulgaria.

The short-term variation covered studies of intense precipitation events, hail storms, and fog. Developed were two-dimensional IWV maps (2D-IWV) and were studied 22 intense precipitation cases in Bulgaria. In one case it was found that the advancement of the dry air mass is well captured along the Balkan mountain range in North Bulgaria. Isolated convective cells were formed in the receding humid air mass at the Black sea region Kaliakra. Strong north-south gradient seen in the GNSS 2D-IWV maps was confirmed by the Meteosat 2D-IWV maps. Promising results for application of GNSS-IWV for fog diagnosis and prognosis were obtained in 3 case studies in 2012. The following behaviour of IWV was established: 1) decreasing trend during fog formation (i.e. shows sensitivity to onset of condensation), 2) increasing trend during fog dissipation and 3) high sensitivity of IWV to advection of new air mass at altitude as well as air mass transformation. Ongoing is also a study with hail storm development in 2012.

The long-term IWV variation studies include the 2007 heat wave and comparisons with regional ALADIN-climate model and ERAInterim at station Sofia for 8 year period. During the July 2007 heat wave in Bulgaria a negative GNSS-IWV anomaly was found and confirmed by the IWV derived from the radiosonde. The annual IWV cycle at Sofia was found to be well captured in the ERAInterim reanalysis. The ALADIN-Climate model IWV peaks in July, while the observed GNSSS-IWV peak is in August.

Two short videos presenting the concepts of “GNSS Meteorology” and “GNSS for ionosphere monitoring” ( were produced as part of the project. The “GNSS Meteorology” video has been seen over 900 times on Youtube ( and was used for a lecture for the Space Expo Visit to Sofia in 2014. It was also awarded first place of the Marie Curie Alumni Association (MCAA) Communication Working Group video competition. The “GNSS for ionosphere monitoring” video ( was seen over 250 times within of a week of its presentations on Youtube.

The project resulted in national, regional and European collaborations and integration of the GNSS data from Southeast Europe in test phase for operational provision for EUMETNET – E-GVAP project. Dr. Guerova established a GNSS Meteorology research group of 2 PhD and 5 MSc students. The project resulted in establishment of collaboration with two private companies operating national GNSS network as well as collaboration with the National Institute of Meteorology and Hydrology and the National Institute of Geophysics, Geodesy and Geography. This project created new collaborations within the framework of COST Action ES1206 "Advanced Global Navigation Satellite Systems tropospheric products for monitoring severe weather events and climate (GNSS4SWEC)" (2013-2017). Close collaboration with University of Luxembourg resulted in establishment of the Sofia University GNSS Analysis Centre (SUGAC). SUGAC is the first Analysis Centre in Southeast Europe targeting atmospheric monitoring with the tropospheric products from the ground-based GNSS networks in the region. The first processing campaign took place 2014 with processing 7 Bulgarian GNSS stations for one year deriving tropospheric products with very high temporal resolution (5 minutes). Dr Guerova was elected vice-chair of the COST Action GNSS4SWEC, associate member of the International GNSS Service (IGS) and member of Working group 4.3.3 “Integration of GNSS atmosphere models with NWP models” of the International Association of Geodesy (IAG).

The work during the 2011-2014 period is reported in: 3 journal publication, 5 extended abstracts in conference proceeding, 5 BSc and 3 MSc theses. Dr. Guerova attended: 10 conferences/workshops, 3 invited expert meetings, 2 summer schools and 4 COST working group meetings. She gave in total 39 oral and poster presentations from which 9 are invited oral presentations or lectures, 12/18 are oral/poster presentations. She was featured in 2 interviews and one reportage on the National Television.

The socio-economic impact of the project is three fold: 1) successful development of a regional centre of knowledge in a new topic for the region, 2) establishment of links on national level and impact studies with potential for implementation in severe weather monitoring as well as fog diagnosis and forecasting and 3) establishment of international links, which resulted in extension of the E-GVAP network to the data sparse region of Southeast Europe with operational data provision in test phase.

As a result of this project a regional centre of knowledge on GNSS Meteorology was established in Bulgaria/Southeast Europe . The topic is new for the region and bridged the existing gap and strengthened the Southeast Europe's research capacity. Recruiting a researcher with in-depth knowledge of the topic initiated work on state-of-the-art research topics for which Southeast Europe has a potential to play a leadership role. Application of GNSS tropospheric products in fog diagnosis shows a promise for integration in operational fog forecasting. The topic is developed in collaboration with the partners from the GNSS4SWEC community. Establishment of the first in Southeast Europe GNSS Analysis centre focused on tropospheric products will further augment the current research capacity in the region and aims at provision of operational GNSS tropospheric products for the E-GVAP service.

For more information about the project please consult the project web site:
or sent an email to Dr. Guergana Guerova at: