Assessing Long Term Trends in the Atmospheric Water Vapor Content by Combining Data From VLBI, GPS, Radiosondes and Microwave Radiometry

Consistent time series of integrated precipitable water vapor (IPWV) are important when estimating long term trends associated with climate change. Space geodetic and remote sensing techniques offer different advantages in terms of a long observation history, instrumental stability, and measurement uncertainty. We use four different techniques at the Onsala Space Observatory on the Swedish west coast namely geodetic VLBI, ground-based GPS, microwave radiometry, and radiosondes. The individual advantages and disadvantages are exploited to assess the long-term trend in the IPWV. A combined linear trend for the IPWV and the time period 1980-2002 is estimated to +0.17 ± 0.01 mm/yr.