MUSICA (“MUlti-platform remote sensing of Isotopologues for investigating the Cycle of Atmospheric water”, http://www.imk-asf.kit.edu/english/musica.php) is a European Research Council (ERC) project. The project has developed tropospheric water vapour isotopologue retrievals (H2O and H2O-δD pairs) using ground-based FTIR spectra as well as thermal nadir spectra measured by the satellite sensor IASI. H2O-δD pairs allow studying tropospheric water transport pathways and in combination with models they can improve our understanding of important climate feedback mechanisms (see also WCRP Grand Challenges: http://www.wcrp-climate.org/grand-challenges). For MUSICA, the FTIR spectra have been analysed centrally at KIT using uniform and consistent retrieval settings, thereby guaranteeing ultimate consistency of the retrieval products generated for different FTIR stations. The FTIR products are H2O profiles for the lower, middle and upper troposphere as well as H2O-δD pairs for the lower and middle troposphere. The data have been produced for 12 FTIR stations and date back to 1996. The dataset has been extensively characterized and validated (theoretically and empirically). Furthermore, the spectra have been used to perform uniform retrievals of XCO2, which is then used for documenting the long-term stability of these kind of FTIR data. The data are provided in the form of two data types. The first type ("ftir.iso.h2o") is best-suited for tropospheric water vapour distribution studies that disregard the different isotopologues (comparison with radiosonde data, analyses of water vapour variability and trends, etc.). The second type ("ftir.iso.post.h2o") is needed for analysing moisture pathways by means of H2O-δD pair distribution. The data format is hdf4 and the files have been generated in compliance with GEOMS (Generic Earth Observation Metadata Standard). The complete MUSICA NDACC/FTIR dataset is also publicly available via the NDACC database (ftp://ftp.cpc.ncep.noaa.gov/ndacc/MUSICA). Details on the characteristics of the dataset are described in the paper "Tropospheric water vapour isotopoloque data (H\(_{2}^{16}\)O, H\(_{2}^{18}\)O and HD16O) as obtained from NDACC/FTIR solar absorption spectra" that has been prepared for ESSD in the context of the special issue “25th anniversary of NDACC”.

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