GNSS-MET - Rapid Delivery of Tropospheric Wet Delays Based on GNSS Observations for Weather Forecast

The aim of the project is to provide GNSS based measurements of the tropospheric water vapour content to be used within the INCA system.

Short Description

The importance of high resolution meteorological analysis of the mountain atmosphere has increased in recent years due to local and regional extreme precipitation. A detailed analysis of the humidity field is an important precondition for better monitoring and better forecasting of these events. For this reason, ZAMG has operated the spatial and temporal high resolution INCA system (INCA = Integrated Nowcasting through Comprehensive Analysis) since the beginning of 2005. Errors in this analysis occur mainly in alpine areas where the predicted models do not reproduce the atmosphere correctly.

We obtain GNSS reference station data from the network KELSAT (operated by the KELAG company) covering the mountainous area of Carinthia. KELSAT represents one of the still very rare networks observing both GPS+GLONASS satellites and therefore offers an almost unique environment for this project.

When GNSS (GPS, GLONASS, in future GALILEO) satellite microwave signals are transmitted through the atmosphere, they are affected by the media. One of those components is the tropospheric refraction. The tropospheric time delay can be split up into the hydrostatic part, calculated from pressure and temperature measurements at the observing station, and into a wet component, describing the rapid variable water vapour content of the troposphere.

To separate the hydrostatic part from the wet contribution we use ground measurements from nearby located Meteorological Sensor Stations (TAWES network). The remaining Wet Delay (ZWD) may be converted into Integrated Water Vapour (IWV) if the temperature at the GNSS Sensor Station is available, too. In sum, the GNSS based ZWD is an integral value, but available with high temporal resolution and horizontal resolution.

To contribute to operational numerical weather prediction the water vapour content has to be made available within 45-60 minutes. The Water Vapour estimates are forwarded to ZAMG to investigate and validate their potential and usefulness for operational weather forecasting.

Project Partners


University of Technology Vienna, Institute of Geodesy and Geophysics - Ao. Prof. Dr. Robert Weber


  • Zentralanstalt für Meteorologie und Geodynamik-ZAMG - Dr. Thomas Haiden
  • KELAG-Kärntner Elektrizitäts-Aktiengesellschaft - Dipl.Ing. Harald Felsberger

Contact Address

University of Technology Vienna, Institute of Geodesy and Geophysics
Ao. Prof. Dr. Robert Weber
Gußhausstrasse 27-29 / E128
A-1040 Wien
Tel.:+43 (1) 58801 12865