GNSS Precipitable Water Vapour for Climate Monitoring

Abstract

Aside from main geodetic applications, the Global Navigation Satellite System (GNSS) is now an established observing system for atmospheric water vapour which is the most important greenhouse gas as it is responsible for around 60% of the natural greenhouse effect. Water vapour is under-sampled in the current climate-observing systems. Obtaining and exploiting more high-quality humidity observations is essential for climate research. Established in 2006, the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN), is an international reference observing network of sites measuring essential climate variables above the Earth's surface. Currently, this network comprises more than 30 reference sites worldwide, designed to detect long-term trends of key climate variables such as temperature and humidity in the upper atmosphere. GRUAN observations are required to be of reference quality, with known biases removed and with an associated uncertainty value, based on thorough characterization of all sources of measurement. 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 precipitable water vapour (GNSS-PWV) measurement has been included as a priority one measurement of the essential climate variable water vapour to both GRUAN and WegenerNet climate station networks. GFZ contributes to climate research within GRUAN and WegenerNet with its expertise in processing of ground-based GNSS network data to generate precise PWV products. GFZ is responsible for the installation of GNSS hardware, data transfer, processing and archiving, derivation of GNSS-PWV data products according to GRUAN and WegenerNet requirements including PWV uncertainty estimation. GNSS-PWV products and results of selected validation studies will be presented.