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

Abstract : 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, CS, 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 CS 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 CS temperature dependence is discussed in relation with FTS measurements at high temperature.

Foreign-continuum cross-sections, CF, 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, CF 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 CF 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 CF values is used to derive from a polynomial fit, the empirical frequency dependence of CF(ν) over the 4250-5000 cm-1 range. Overall, the semi-empirical MT_CKD_3.5 values of CF are significantly underestimated in the centre of the considered window.

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https://hal-insu.archives-ouvertes.fr/insu-03706391
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Submitted on : Monday, June 27, 2022 - 4:15:12 PM
Last modification on : Wednesday, June 29, 2022 - 3:32:37 AM

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H. Fleurbaey, R. Grilli, D. 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, ⟨10.1016/j.jqsrt.2021.108004⟩. ⟨insu-03706391⟩

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