GNSSMET-AUSTRIA - GNSS based determination of atmospheric humidity changes and their assimilation into operational weather forecast systems

In the framework of project GNSSMET AUSTRIA the wet part of the tropospheric delay is estimated with a temporal resolution of one hour and an accuracy of better than +/- 1mm PW based on observations of a GNSS reference network covering more than 30 stations distributed over the whole Austrian territory. These values are assimilated within the ALADIN-Austria model operated at the Central Institute for Meteorology and Geodynamics (ZAMG).

Short Description

The distribution of Water Vapour within the lower atmosphere is a determining factor of the weather conditions and therefore plays an essential role within short-term forecast models but also for long term climate studies. Unfortunately, this distribution is usually not very well known or understood with acceptable high temporal and spatial resolution.

The microwave signals of the GNSS satellites (GPS, GLONASS and in future GALILEO) are time delayed when passing the atmosphere. Therefore the tropospheric delay (as part of the atmospheric delay) and subsequently the humidity distribution within the troposphere can be estimated from the microwave observations. The tropospheric delay is usually comprised of a well understood hydrostatic component and of the rapidly time varying wet component.

The remaining wet component can be assimilated in numerical weather models. It has been proved that e.g. passing weather fronts can better be analysed by introduced GNSS derived tropospheric wet delays because this data is influenced by changes in humidity in the free atmosphere, whereas the data at the meteorological ground stations reacts to these changes only with a time delay.

This allows to forecast heavy rainfall causing potentially local floodings more reliably and to narrow down the affected region. To contribute efficiently to weather forecast the water vapour content has to be known within a delay of less than one hour. This demand is hard to fulfil because of data transfer delays and considerable processing times due to the huge amount of GNSS observation data.

New modelling schemes to derive the signal delay are examined. This concerns the derivation of wet delays by means of a mixed network and PPP (Precise Point Positioning) approach as well as the implementation of new mapping functions like the GMF. Last but not least the direct signal delay along the ray path shall be used to establish a 3D- model of refractivity (GNSS tomography).

Project Partners


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


  • Central Institute for Meteorology and Geodynamics - Yong Wang
  • Wienstrom GmbH - Christian Klug
  • KELAG-Kärntner Elektrizitäts-Aktiengesellschaft - Harald Felsberger

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