Research Group
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Centre of Excellence (STCE)

The EUMETNET EIG GNSS water VApour Program (E-GVAP)

The EUMETNET EIG GNSS water VApour Program (E-GVAP) is a program running under the aegis of the European Network of Meteorological Service (EUMETNET). It is based on the 20+ years of knowledge and expertise gained during previous European innitiatives in the field, mainly the COST-716 Action (1998-2004) and the TOUGH Project (E.C. 5th FP, 2003-2006).

E-GVAP started in April 2005 (and is still running today) with the objective to collect Near Real-Time (NRT) ground-based GNSS tropospheric delay and water vapour estimates on the European scale. This information is provided to EUMETNET partners for operational meteorology. The ultimate goal of the project is to improve weather forecasts and nowcasts. The long-term goal is to be integrated as a permanent observing system within the EUMETNET Composite Observing System (EUCOS) and/or the future WMO Information System (WIS).

A Fruitfull Meteorology - Geodesy Collaboration

Complte E-GVAP Observing Network

Figure 1: Map of the GNSS ground stations used by the E-GVAP data analysis centres and for which tropospheric delays are computed (status: 12 Augustus 2010)

E-GVAP is based on a combination of centralised functions, which are carried out by the E-GVAP management team, and distributed functions, which are handled by the European National Meteorological Service (ENMS) members in collaboration with their geodetic colleagues. The E-GVAP objective is achieved in close collaboration with the geodetic community who operate the 11 analysis centres that provides operationnaly the NRT tropospheric delay estimates. ROB maintains one of these GNSS analysis centres.

In practice, thanks to the coordination of E-GVAP, the observations from permanent GNSS tracking stations distributed all over Europe (Figure 3) are now routinely analysed each hour by a set of voluntary GNSS data analysis centres. Each of these GNSS data analysis centres provides E-GVAP in near real-time with tropospheric Zenith Total path Delays (ZTD) from a European regional sub-network. These GNSS delay data are then used by the European National Meteorological Services (ENMS) for weather forecasting and nowcasting applications. Altogether, the GNSS data analysis centres process observations from about 1250 unique sites (status: August 2010). Over the last years, this number has grown with more than 200 new sites a year to reach as today 2100+ sites.

The GNSS observation sites used in E-GVAP mainly belong to two categories of GNSS networks: on one hand, to international public networks such as the International GNSS Service (IGS) network and the EUREF Permanent Network (EPN), and on the other hand to national and/or private networks such as the ones operated by National Mapping and Cartographic Agencies (NMCA).

An Example of GNSS-Meteorology

Figure 2a: Observed rain

Figure 2b: Forecast rain with GNSS

Figure 2c: Forecast rain without GNSS

The following example is taken from the E-GVAP website. These figures show a case with significant improvement of a precipitation forecast when ground-based GNSS observations are included to calculate the exptected future weather. The top-right picture shows the observed rain over a 12-hour period. Below are the predicted amounts over the same period with (left picture) and without (right picture) GNSS observations respectively. Green, yellow, red, and violet colors indicate severe large amounts of rain, with violet being the highest.