Measured and predicted atmospheric transmission in the 40–53-μm region, and the contribution of continuum absorption by CO_2 and N_2

Abstract

High resolution measurements of atmospheric transmission of sunlight from space to altitudes of 12.2 km, 8.53 km, and 5.48 km made over Johnston Island are reported. The spectral region covered is 4.0-5.3 microm. Comparisons of the measured transmission with theoretically synthesized transmission curves are presented. It is shown that the sharp spectral features due to molecular line-by-line absorption can be predicted accurately while the modeling of the continuum absorption features needs further development. A discussion of the current models for CO(2) and N(2) continuum absorption is presented. An alternative mechanism is proposed for continuum absorption, which is based on the spectral properties of atmospheric van der Waals molecular complexes such as CO(2).N(2) and N(2).N(2) dimers.

Stratospheric measurements of continuous absorption near 2400 cm^−1

“…Normalization of the line shape function requires S = Sk dv; for lower stratospheric conditions this relation is satisfied to better than 0.1% with all four far-wing line shape functions. As noted by Bernstein et al, 31 most of the absorption beyond the band head at room temperature and reduced temperatures is contributed by the tails of distant lines near the intensity maximum of the R branch of the intense 3 band. and Burch et al 4 (curve 4 of Fig.…”