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-dD pairs) using ground-based 
FTIR spectra as well as thermal nadir spectra measured by the satellite sensor IASI. H2O-dD 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-dD pairs for the lower 
and middle troposphere. The data have been produced for 12 FTIR stations and date back to 1996. Ten of these FTIR 
stations belong to NDACC. The two stations Karlsruhe and Addis Ababa currently don't belong to NDACC but plan 
to become official NDACC sites.

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. Details on the characteristics of the dataset are described in a paper that 
has been prepared for ESSD in the context of the special issue “25th anniversary of NDACC” (can be lined to this 
description once published).