CONTRIBUTION TO THE DEVELOPMENT OF RADIATIVE-TRANSFER MODELS FOR HIGH-SPECTRAL-RESOLUTION OBSERVATIONS IN THE INFRARED

The capability of the Automatized Atmospheric Absorption atlas method for raditaive transfer modelling to simulate analytic Jacobians (first partial derivative of the observations with respect to the geophysical parameters) is analyzed. Several applications based on analytical Jacobians are described. The sensitivity of a '1200 resolution' infrared spectrum to the water vapor content in the lower atmosphere is found to be weak, however a significant sensitivity to the methane give us good confidence in a successful retrieval of its total atmospheric content from high spectral resolution nadir viewing sounders. The degree of linearity of the radiative transfer equation with respect to the temperature and the water vapour is quantified. The continuum absorption is found to contribute to the non-linear behavior of channels located around 750 cm(-1) for wet atmospheres. The highest degree of non-linearity is found at the end of the CO2-4.3 mu m absorption band. The rest of the spectrum can be considered to linearly answer to individual perturbations < 5K and 50% of the temperature and the water vapor atmospheric layers respectively. When all the geophysical parameters are simultaneously perturbed over the whole column, the non-linearities remain rather weak, provided the individual layer perturbations are in the order of those taken into account previously.