Climate monitoring using GPS

We present results on long-term trends of integrated precipitable water vapor (IPWV) over the Scandinavian region based on data from the Swedish permanent Global Positioning System (GPS) network, obtained during the period August 1993 to the end of 2000. We assess the magnitude of the effects on the estimated IPWV caused by antenna radome changes by comparisons with other independent techniques, such as microwave radiometry and radiosondes. The agreement between the techniques is at I nun level for the IPWV content and at 0.1 mm/yr for the estimated linear trend. Using the IPWV differences between the techniques, we assess the effects of radome changes to be in the interval 0-1.8 mm depending on the type of radome used. The estimated trends of IPWV over Scandinavia show a general increase of 0.1-0.2 mm/yr, and are more pronounced in the south-west region. We also estimate trends based on summer and winter periods. We find them to be larger for the winter periods compared to the summer in the southern parts and the opposite in the northern regions of Scandinavia. (C) 2002 Elsevier Science Ltd. All rights reserved.