RAPID COMPUTATION OF SPECTRALLY INTEGRATED NONLOCAL THERMODYNAMIC-EQUILIBRIUM LIMB EMISSION

The interpretation of infrared radiance measurements made by;satellite -borne limb-scanning broadband radiometers requires accurate and compu tationally fast techniques with which to evaluate the equation of radi ative transfer. This requirement is made even more stringent when anal yzing measurements of non-local thermodynamic equilibrium (non-LTE) em ission from the terrestrial mesosphere and lower thermosphere. In prin ciple, line-by-line calculations which explicitly account for the depa rture from thermodynamic equilibrium in both the source functions and the transmittances are necessary. In this paper we extend the emissivi ty growth approximation (EGA) technique developed for local thermodyna mic equilibrium (LTE) conditions to the non-LTE environment. Computati ons of the non-LTE spectrally integrated limb radiance for the molecul ar oxygen dayglow (1.27 mu m and 762 nm), ozone and carbon dioxide in the 9- to 11-mu m spectral interval, carbon monoxide (4.6 mu m), nitri c oxide (5.3 mu m), and the carbon dioxide bands (15 mu m) are present ed. Using the non-LTE form of the EGA, the spectrally integrated limb emission is calculated for 35 tangent heights in the mesosphere and lo wer thermosphere (a total of 1200 atmospheric layers) with Line-by-lin e accuracy in similar to 0.35 s of CPU time on readily available deskt op computer hardware, while the corresponding line-by-line calculation s may require several minutes. The non-LTE EGA technique will allow ki netic temperature and minor constituent retrieval algorithms to readil y include non-LTE effects limited only by the a priori knowledge of th e departure from LTE in the observed bands.