Observed atmospheric collision‐induced absorption in near‐infrared oxygen bands

A recent high-resolution measurement of surface solar radiance taken under cloud-free conditions by the Absolute Solar Transmittance Interferometer shows clear indication of continuum absorption associated with the three strongest O2 a1 Δg ← X3Σg− transitions. The differences between these measurements and a calculation by the line-by-line radiative transfer model (LBLRTM) were used to determine the properties of these collision-induced bands and, for two of the bands, led to parameterizations of the spectral behavior of the absorption coefficients. The results indicate that these continuum bands absorb 0.84 W/m2 at the 71.5° solar zenith angle associated with the observation. For the observed 3000–9965 cm−1 spectrum, with the exception of the spectral range in which this collision-induced absorption occurs, there is good agreement between the measured and calculated radiance values, with no evidence for discrete absorption by unknown gases.

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