Knowledge Bank

We are validating line parameters for CO$2$ at 1.61 $\mu$m and 2.07 $\mu$m using high resolution atmospheric spectra and a new retrieval algorithm [1, 2] being developed for the Orbiting Carbon Observatory (OCO-2) in order to estimate column-averaged mixing ratio of CO$2$, X, to a sub-1% precision. This requirement demands highly accurate molecular line shape models. We tested a combination of line mixing [3] with speed dependent Voigt shapes [4,5] obtained from laboratory spectra using a state of the art multi-spectrum fitting procedure [6, 7]. The atmospheric tests were made with a diverse set of over 400 soundings including upward- and downward-looking FT-IR data from the Total Carbon Column Observing Network (TCCON), and the data from TANSO-FTS spectrometer aboard the Greenhouse gases Observing SATellite (GOSAT), respectively. The new absorption cross sections significantly reduced residuals in the spectral fit in the 2.07 $\mu$m region, while the effects on the 1.61 $\mu$m band are less definitive but still suggest some improvement. Overall these tests favor the adoption of the new models. 2012; 5:99-121. [2] Crisp, D., et al. {\it AMTD} 2012; 5:1 - 60. [3] Hartmann, J. M., et al. {\it ACP} 9:7303-7312. [4] Devi et al., {\it J. Mol.Spec.} 2007; 245:52-80. [5] Benner et al. 66th International Symposium on Molecular Spectroscopy, Columbus OH (2011). [6] Benner, D.C., et al., {\it JQSRT} 1995; 53(6):705 - 721. [7] Letchworth, K.L., et al. {\it JQSRT}, 107: 173 - 192.}