SPECTRAL-LINE SHAPE CONSIDERATIONS FOR LIMB TEMPERATURE SOUNDERS

The sensitivity of radiative transfer calculations to spectral line shape models is investigated for two CO2 spectral regions used by instruments aboard the Upper Atmosphere Research Satellite for making low-altitude temperature and pressure retrievals. Line shape models have been tested by comparing calculated spectra with observations made by the Atmospheric Trace Molecule Spectroscopy experiment. Spectral line mixing is discussed and shown to be important at the 617 cm-1 Q branch where its inclusion in the radiative transfer model can lead to differences of more than 2 K in brightness temperature at low tangent heights. The sub-Lorentzian line wings of the CO2 nu-2 band must be correctly modeled in calculations at the 791 cm-1 Q branch otherwise equivalent brightness temperatures for a 15 km limb view will be in error by as much as 10 K.