Constrained profile retrieval applied to the observation mode of the Michelson Interferometer for Passive Atmospheric Sounding

To investigate the atmosphere of Earth and to detect changes in its environ ment, the Environmental Satellite will be launched by the European Space Ag ency in a polar orbit in October 2001. One of its payload instruments is a Fourier spectrometer, the Michelson Interferometer for Passive Atmospheric Sounding, designed to measure the spectral thermal emission of molecules in the atmosphere in a limb-viewing mode. The goal of this experiment is to d erive operationally vertical profiles of pressure and temperature as well a s of trace gases O-3, H2O, CH4, N2O, NO2, and HNO3 from spectra on a global scale. A major topic in the analysis of the computational methodology for obtaining the profiles is how available a priori knowledge can be used and how this a priori knowledge affects corresponding results. Retrieval method s were compared and it was shown that an optimal estimation formalism can b e used in a highly flexible way for this kind of data analysis. Beyond this , diagnostic tools, such as estimated standard deviation, vertical resoluti on, or degrees of freedom, have been used to characterize the results. Opti mized regularization parameters have been determined, and a great effect fr om the choice of regularization and discretization on the results was demon strated. In particular, we show that the optimal estimation formalism can b e used to emulate purely smoothing constraints. (C) 2001 Optical Society of America.