A multi-instrument comparison study of integrated water vapor over Kiruna, Sweden

Water vapor plays an important role in the earths atmosphere. It is the strongest and most abundant greenhouse gas and strongly affects the weather and climate. However, because of its large temporal and spacial variability it is a demanding task to measure. Water vapor has long been continually measured by radiosondes at research facilities around the globe but such stations are missing in the polar regions. Many different techniques have been developed and global coverage is now available via satellite borne instruments, although it is still a demanding task to measure correctly. This thesis compares measurements of integrated water vapor (IWV) over Kiruna, Sweden, from a number of different instruments. Ground based remote sensing instruments include a Fourier transform infrared (FTIR) spectrometer, an ozone microwave radiometer and a GPS instrument. Satellite measurements are included from the microwave radiometer AMSU-B on the NOAA series of satellites and lastly in situ measurements from radiosondes are also used. The GPS instrument measures continually, with high quality, every two hours all year round and is therefore used as the reference in the comparison. For the AMSU-B instruments an algorithm combining three different channels is used to derive IWV. The results show good agreement with the GPS and low standard deviation under 20%. The FTIR also shows very good agreement with low standard deviation of around 15%, partly because of its limitation to only measure at cloud free conditions, usually meaning stable atmospheric conditions. The microwave performs worst with a standard deviation of around 30% but still shows fair agreement to the GPS. This is to a certain degree expected as water vapor is only a byproduct from the radiometer. Lastly the radiosondes produce very good results with the highest correlation and lowest standard deviation of 13%.Validerat; 20101217 (root