GNSS for Weather Forecast and Climate Research at GFZ

Global Navigation Satellite System (GNSS) is an established atmospheric observing system for atmospheric water vapour with high spatiotemporal resolution. Water vapour is under-sampled in the current meteorological and climate-observing systems, and thus obtaining and exploiting more high-quality humidity observations is essential.  The operational GNSS data processing at GFZ provides all tropospheric products, zenith total delays (ZTD), precipitable water vapour (PWV), slant total delays (STD) and tropospheric gradients in the framework of different meteorological projects like e.g. E-GVAP ("The EUMETNET EIG GNSS Water Vapour Programme", http://egvap.dmi). E-GVAP is in charge of the collection and quality control of operational GNSS tropospheric products for numerical weather prediction. GFZ is one of the E-GVAP Analysis Centres and processes about 600 GNSS stations in near real-time. The tropospheric products provided by GFZ are used by European weather services for operational forecasts.  GFZ contributes to climate research within the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN). Established in 2006, GRUAN, is an international reference observing network of sites measuring essential climate variables above the Earth's surface. Currently, this network comprises 33 reference sites worldwide, designed to detect long-term trends of key climate variables such as temperature and humidity. GFZ hosts a central processing facility for the GNSS data and is responsible for the installation of GNSS hardware, data transfer, processing and archiving, as well as derivation of GNSS-PWV products according to the GRUAN requirements. A complementary small scale regional climate station network is the Austrian WegenerNet, which provides since 2007 measurements of hydrometeorological variables with very high spatial and temporal resolution. GNSS-PWV measurements have been included as a priority one measurement of the essential climate variable water vapour to both GRUAN and WegenerNet climate station networks.GNSS-derived tropospheric products and results of selected validation studies will be presented.