MODELING AND RETRIEVAL OF ATMOSPHERIC SPECTRA USING ASIMUT

The Earth’s atmosphere is continuously changing either on a local or on a global scale. A major challenge for the scientific community is to better understand the involved physico-chemical mechanisms. This requires accurate measurements of trace gases in both the stratosphere and the troposphere. Fourier transform spectroscopy is a powerful technique which is used under various conditions: in ground-based observatories, with balloon-borne instruments, and most recently on board satellites. Inversion of FTIR radiances provides information on the total column abundances, and in some cases on the vertical distributions of several key species. The ASIMUT software has been developed to exploit the synergy existing between the growing number of different instruments working under different geometries. The main particularities of the software are: (i) The possibility to retrieve columns and/or profiles of atmospheric constituents simultaneously from different spectra, which may have been recorded by different instruments or obtained under different geometries. This allows the possibility to perform combined retrieval, e.g., of a ground based measurement and a satellite-based one probing the same air mass, or from spectra recorded by different instruments on the same platform; (ii) The analytical derivation of the Jacobians; (iii) The use of the Optimal Estimation method (OEM), using diagonal or full covariance matrices; (iv) Its portability; (v) Its modularity, hence the ease to add future features. Initially developed for the Earth atmosphere, its applicability can be extended to extraterrestrial atmospheres.