| Summary: | Volume mixing ratio water vapour profiles have been retrieved from IASI (Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) processor. The retrievals are done for IASI observations that coincide with Vaisala RS92 radiosonde measurements performed in the framework of the GCOS (Global Climate Observing System) Reference Upper-Air Network (GRUAN) in three different climate zones: the tropics (Manus Island, 2°S), mid-latitudes (Lindenberg, 52°N), and polar regions (Sodankylä, 67°N). The retrievals show good sensitivity with respect to the vertical H2O distribution between 1km above ground and the upper troposphere. Typical DOFS (degrees of freedom for signal) values are about 5.6 for the tropics, 5.1 for summertime mid-latitudes, 3.8 for wintertime mid-latitudes, and 4.4 for summertime polar regions. The errors of the MUSICA IASI water vapour profiles have been theoretically estimated considering the contribution of many different uncertainty sources. For all three climate regions, unrecognized cirrus clouds and uncertainties in atmospheric temperature have been identified as the most important error sources and they can reach about 25%. This research has largely benefited from results of the projects MUSICA (funded by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement number 256961), MOTIV (funded by the Deutsche Forschungsgemeinschaft under GZ SCHN 1126/2-1), and INMENSE (funded by the Ministerio de Economía y Competividad from Spain, CGL2016-80688-P).
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