1UPMC Université Paris 06, CNRS UMR8190, LATMOS/IPSL, France
2Spectroscopie de l'Atmosphère, Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles (ULB), Brussels, Belgium
3Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
5NASA Langley Research Center, Hampton, Virginia, USA
6Center for Satellite Applications and Research, National Environmental Satellite, Data and Information Service, NOAA, Camp Springs, Maryland, USA
*now at: UPMC Université Paris 06, Laboratoire de Météorologie Dynamique/IPSL, Ecole Polytechnique, Palaiseau, France
Abstract. The Infrared Atmospheric Sounding Interferometer (IASI) onboard the MetOp satellite measures carbon monoxide (CO) on a global scale, twice a day. CO total columns and vertical profiles are retrieved in near real time from the nadir radiance spectra measured by the instrument in the thermal infrared (TIR) spectral range. This paper describes the measurement vertical sensitivity of IASI. On the global scale, 0.8 to 2.4 independent pieces of information are available for the retrieval. At mid latitudes, the information ranges between 1.5 and 2, which enables the lower and upper troposphere to be distinguished, especially when thermal contrast is important. Global distributions of column CO are evaluated with correlative observations available from other nadir looking TIR missions currently in operation: the Measurements of Pollution in the Troposphere (MOPITT) onboard TERRA, the Atmospheric Infrared Sounder (AIRS) onboard AQUA and the Tropospheric Emission Spectrometer (TES) onboard AURA. On the global scale and on average, total column discrepancies ranging from 10 to 15% are found for latitudes above 45° N and lower than 15° S, but can reach 30% in cases of strong CO concentrations, e.g. when fires events occur. The choice of the a priori assumptions influences the retrievals and can explain some of the observed differences. Instrument specifications of IASI versus other missions are also discussed.