Measurements of the water vapor continuum absorption by OFCEAS at 3.50 µm and 2.32 µm

H Fleurbaey (1) , R Grilli (2) , Didier Mondelain (3) , A Campargue (1)

1 LAME-LIPhy - LAsers, Molécules et Environnement
2 IGE - Institut des Géosciences de l’Environnement
3 LIPhy - Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]

Measurements of the water vapor absorption cross-sections at two spectral points of the 2.1 μm and 4.0 μm transparency windows are performed by optical feedback cavity enhanced absorption spectroscopy (OFCEAS). The self-continuum cross-section, C S , is measured for temperature values of 30 and 47 °C (303 and 320 K) at the 2853 cm −1 spectral point, corresponding to the lowest opacity region of the 4.0 μm transparency window. The C S values derived from the pressure squared dependence of the self-continuum, are found consistent with previous CEAS measurements in the considered window but significantly smaller than measurements by Fourier transform spectroscopy (FTS). The C S temperature dependence is discussed in relation with FTS measurements at high temperature. Foreign-continuum cross-sections, C F , are newly obtained from OFCEAS spectra of moist air in flow regime at the 4302 cm −1 spectral point of the low energy edge of the 2.1 μm window. After subtraction of the monomer and self-continuum contributions, C F values are derived from the linear variation of the foreign-continuum absorption with the product of the water vapor and air partial pressures. The measurements were performed for temperature values of 34 and 47 °C (307 and 320 K) and no significant temperature dependency was observed. The present C F value at 4302 cm −1 is gathered with previous CEAS measurements at seven spectral points of the 2.1 μm window. This consistent set of C F values is used to derive from a polynomial fit, the empirical frequency dependence of C F (ν) over the 4250-50 0 0 cm −1 range. Overall, the semi-empirical MT_CKD_3.5 values of C F are significantly underestimated in the centre of the considered window.

Mots clés: Water vapor; continuum absorption; MT_CKD model; OFCEAS; transparency window; atmosphere

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Chimie-Physique [physics.chem-ph]

H Fleurbaey, R Grilli, Didier Mondelain, A Campargue. Measurements of the water vapor continuum absorption by OFCEAS at 3.50 µm and 2.32 µm. Journal of Quantitative Spectroscopy and Radiative Transfer, 2022, 278, pp.108004. ⟨10.1016/j.jqsrt.2021.108004⟩. ⟨hal-03854932⟩