Improved atmospheric radiance calculations using CO2 P/R-branch line mixing

S. De Souza-Machado; L. Larrabee Strow; David C. Tobin; Scott E. Hannon

doi:10.1117/12.373071

8 December 1999 Improved atmospheric radiance calculations using CO₂ P/R-branch line mixing

S. De Souza-Machado, L. Larrabee Strow, David C. Tobin, Scott E. Hannon

Proceedings Volume 3867, Satellite Remote Sensing of Clouds and the Atmosphere IV; (1999) https://doi.org/10.1117/12.373071
Event: Remote Sensing, 1999, Florence, Italy

Abstract

New high-spectral resolution satellite sounders will use channels located between CO2 lines for temperature retrievals. Transmittances for these channels are dominated by spectral line wings that are strongly influenced by line-mixing and duration-of-collision effects. Previous studies demonstrated the importance of Q-branch line mixing for atmospheric sounding in the 15 micrometer region. This work presents an improved model of P/R-branch line mixing and duration-of- collision effects on CO2 transmittances in the 4.3 micrometer and 15 micrometer regions, based on laboratory and spectroscopy data. Most line-by-line codes model non- Lorentzian behavior by using the Cousin chi-function. This empirical function incorporates both P/R line-mixing and duration-of-collision effects by using many parameters. It is common to use the Cousin model parameters obtained from the 4 micrometer band in the 15 micrometer region, overestimating the amount of line-mixing. Comparisons to radiance data taken with high resolution interferometers that fly on NASA's ER-2 partially validates our model. The biggest improvements are at 4.3 micrometer where the differences are reduced by more than 2K, compared to using the Cousin model.

Citation Download Citation

S. De Souza-Machado, L. Larrabee Strow, David C. Tobin, and Scott E. Hannon "Improved atmospheric radiance calculations using CO₂ P/R-branch line mixing", Proc. SPIE 3867, Satellite Remote Sensing of Clouds and the Atmosphere IV, (8 December 1999); https://doi.org/10.1117/12.373071

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