Geodetic Institute (GIK)

Monitoring of atmospheric water vapor by the analysis of GNSS signals and SAR data

The neutrospheric delay composes of hydrostatic and non-hydrostatic components. Modeling the hydrostatic component is rather simple since it depends only on air pressure and temperature. The non-hydrostatic component is dominated by the atmospheric water vapor content. Therefore, the terms “wet” and “dry” are often used for characterizing the non-hydrostatic and hydrostatic parts. In contrast to the hydrostatic component the wet part is strongly variable in time and space. Although the wet component amounts only for about 10% of the total neutrospheric delay, its effect is considered significant in the applications of high-precision positioning by GNSS (Global Navigation Satellite Systems, e.g. GPS) and InSAR (Interferometric Synthetic Aperture Radar) applications such as the digital terrain modeling and the extraction of Earth’s crust displacements maps.

Advanced numerical estimation techniques allow separating the GNSS and InSAR phase observations in such a way that the residuals contain relevant signals from the water vapor content along the propagation path. The idea to use GNSS phase observations received on fixed sites on the Earth’s surface for determining the water vapor content originated in the early 1990ties. Recently, in some regions GNSS-based water vapor data has been integrated into numerical weather models showing e.g. significant improvement in model prediction of rainfall. Investigations related to the impact of water vapor on SAR observations is relatively a new research theme mainly arose by research on high-precision InSAR processing in the new German satellite missions TerraSAR-X (launched 2007) and TanDEM-X (launched June, 2010). The great potential for future, especially due to the large and continuous coverage of InSAR images, has been already recognized and yet many scientific questions related to modeling and estimating water vapor are still open.

The main objective of this project relates to further developments of analytical and numerical models as well as respective estimation techniques to retrieve the distribution of the water vapor in the atmosphere both in space and time from GNSS and InSAR phase observations. A particular focus is put on the potential of the spatial/temporal fusion of InSAR and GNSS phase observations for the estimation of neutrospheric delays. The underlying space-time models need to be further developed and their potential improvement of numerical weather models needs to be investigated. It is expected that the integration of different data sources including meteorological data can better exhaust the specific properties and advantages of the various data types. For long-term monitoring, the natural laboratory of the Upper Rhine Graben (URG) is selected. This region is well covered by meteorological sites providing a possibility for inter-technique comparisons; furthermore, due to the vicinity to the KIT additional observation campaigns are easily manageable at special weather conditions. Also a dense permanent GNSS network exists in the region between the Vosges mountains and the Palatine forest on one side and the Black forest on the other side, this continuously operating network provides a unique opportunity to study the atmospheric water vapor content and the integrated precipitable water over the whole year. It is expected that the methodological and practical results obtained in these processes for this challenging region can be transferred to other regions and global investigations.

Kooperationspartner KIT:

externe Kooperationspartner:

  • Landesamt für Geoinformation und Landentwicklung Baden-Württemberg
  • Landesamt für Vermessung und Geobasisinformation Rheinland-Pfalz
  • Bundesamt für Landestopografie swisstopo (Schweiz)
  • Institut de Physique du Globe de Strasbourg