Influence of the interference between water vapor lines on the atmospheric transmission of near-IR radiation

Abstract

The influence of the interference between IR spectral lines of water vapor on the atmospheric transmission has been studied. The calculations have shown that, for a relatively low pressure, the influence of the interference on the line shift is small for most water vapor lines. However, this influence can be significant for lines whose upper vibrational-rotational states are in a strong resonance. Thus, a relation exists between intramolecular resonances of different types, which manifest themselves as a result of an abnormally strong vibrational-rotational interaction and interference arising due to collisional distortion of molecular steady states. The interference between lines distorts the Lorentz shape of a line profile and leads to a nonlinear pressure dependence of the line shift and to an increased absorption in the atmospheric microwindows. The influence of the interference for a horizontal path is small: the largest addition is 3% at a frequency of 12414.07 cm⁻¹. For a slant atmospheric path under summer conditions, the line interference contributes 0.5%, and for winter conditions the influence of the interference is about 1.5%. It is concluded that the line interference increases the absorption in the atmospheric microwindows.