Effect of interferogram smearing on atmospheric limb sounding by Fourier transform spectroscopy

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Abstract
A method is presented for analyzing an absorption spectrum obtained from the interferogram measured by an interferometer operated in the solar occultation mode. In this mode the complete interferogram is smeared with various components of individual interferograms generated by rays passing through different tangent altitudes. It is shown that the effective tangent altitude of the spectrum is the altitude at which the center fringe of the interferogram is recorded and that the other components of the interferogram only define the instrument line shape. The interferogram smearing effectively creates strong sidelobes on absorption lines so that a strong apodization on the interferogram is recommended for the solar occultation experiment. These concepts are applied to retrieve pressure and temperature simultaneously from stratospheric absorption spectra in the CO2 4.3-μm band obtained by a balloon-borne interferometer in 1976 over Palestine, Tex. Included in the analysis of the CO2 4.3-μm band are the continuum absorptions by the pressure-induced N2 fundamental band and by far wings of the CO2ν3 band. The CO2 absorption line is corrected by a sub-Lorentzian function. Excellent agreement is found between the observed and simulated spectra.