Validation of stratospheric water vapour measurements from the airborne microwave radiometer AMSOS

We present the validation of a water vapour dataset obtained by the Airborne Microwave Stratospheric Observing System AMSOS, a passive microwave radiome- ter operating at 183 GHz. Vertical profiles are retrieved from spectra by an optimal estimation method. The useful verti- cal range lies in the upper troposphere up to the mesosphere with an altitude resolution of 8 to 16 km and a horizontal res- olution of about 57 km. Flight campaigns were performed once a year from 1998 to 2006 measuring the latitudinal dis- tribution of water vapour from the tropics to the polar re- gions. The obtained profiles show clearly the main features of stratospheric water vapour in all latitudinal regions. Data are validated against a set of instruments comprising satel- lite, ground-based, airborne remote sensing and in-situ in- struments. It appears that AMSOS profiles have a dry bias of 0 to -20%, when compared to satellite experiments. Also a comparison between AMSOS and in-situ hygrosondes FISH and FLASH have been performed. A matching in the short overlap region in the upper troposphere of the lidar measure- ments from the DIAL instrument and the AMSOS dataset allowed water vapour profiling from the middle troposphere up to the mesosphere.