Mid-tropospheric CO2 retrieval in the tropical zone from AIRS observations

Cyril Crevoisier, Alain Chédin, Sylvain Heilliette, Noëlle A. Scott, Soumia Serrar and Raymond Armante

Proceedings of ITSC XIII, Ste Adèle, Canada, 2003

The new 2378 channel high spectral resolution NASA/Aqua/Atmospheric Infrared Sounder (AIRS) launched in May 2002 is used to retrieve mean concentration of atmospheric carbon dioxide (CO2). A reduced set of AIRS channels, presenting a high sensitivity to variations of the atmospheric CO2 and reduced sensitivities to variations of other atmospheric components, and well covering the mid-troposphere (from 700 hPa to the tropopause), is first selected using the Optimum Sensitivity Profile (OSP) method. A cloud elimination procedure based on AIRS and Atmospheric Microwave Sounding Unit (AMSU) observations is then performed to detect clear fields of view. The resulting AIRS and AMSU measurements, the latter being not sensitive to CO2 variations, are used in a neural network inference procedure. This non-linear regression scheme has already proven its efficiency in the retrieval of mid-tropospheric CO2 from NOAA polar satellites. The first results obtained with AIRS give hope to improve the accuracy of the retrieval. Maps of monthly mean mid-tropospheric CO2 concentration are obtained for a few months in the tropics [20S ; 20N]. The retrievals show good agreements with aircraft observations.

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