Information Content of Infrared Satellite Sounding Measurements with Respect to CO2

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Abstract
Information theory is used to study the capabilities of the new-generation satellite infrared sounders [Atmospheric Infrared Sounder (AIRS) and Infrared Atmospheric Sounding Interferometer (IASI)] for retrieving atmospheric carbon dioxide (CO2) and for contrasting these new instruments with the current system of infrared sounders [Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder/High-Resolution Infrared Radiation Sounder (TOVS/HIRS)]. It is shown that instruments like AIRS and IASI will be able to retrieve column-averaged CO2 mixing ratios with high enough accuracy (order of 1–2 ppmv) to be useful for atmospheric CO2 inversion studies that try to estimate sources and sinks of CO2. On the other hand, the TOVS/HIRS system is only able to retrieve column-averaged CO2 mixing ratios with an accuracy of the same order as the seasonal amplitude of atmospheric CO2 variations (order of 10 ppmv). It is also shown that the constraining a priori covariance matrix has an important effect on what information can be extracted from the observations.