The water vapour self-continuum absorption in the infrared atmospheric windows: new laser measurements near 3.3 and 2.0 µm

Lechevallier, Loic; Vasilchenko, S.; Grilli, Roberto; Mondelain, D.; Romanini, D.; Campargue, A.

doi:10.5194/amt-11-2159-2018

Cited by 39 publications

(33 citation statements)

References 60 publications

(77 reference statements)

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“…These techniques, in particular, cavity ring down spectroscopy (CRDS), have an inherent higher sensitivity than traditional techniques and allow achieving a very high baseline stability of the spectra, which is the most important criterion for the measurement of weak broadband continua. In particular, the long‐standing debate on the amplitude of the very weak water absorption continuum in the atmospheric transparency window has been recently closed from accurate CRDS and OFCEAS measurements (Campargue et al, , and references herein; Lechevallier et al, ; Richard et al, ), the obtained experimental data set being used to adjust the last version (V3.2) of the MT_CKD continuum (Mlawer et al, ).…”

Section: Introductionmentioning

confidence: 99%

Accurate Laboratory Measurement of the O₂ Collision‐Induced Absorption Band Near 1.27 μm

2019

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The atmospheric band of O2 near 1.27 μm plays an important role in determining the air mass from ground or spaceborne atmospheric spectra. This band consists of narrow absorption lines of the anormalΔ1g−XnormalΣnormalg−3()0−00.25emtransitions superimposed to a much broader collision‐induced absorption (CIA) structure. Very accurate CIA binary coefficients, BO2−O2, BO2−N2, and BO2−air, are determined by highly sensitive cavity ring down spectroscopy from low density spectra (0.36 to 0.85 amagat) of pure oxygen and an O2/N2 mixture (20.96%/79.04%) at room temperature over the 7,513–8,466‐cm−1 region. Two cavity ring down spectrometers involving 12 distributed feedback lasers and two external cavity diode lasers were used below and above 7,920 cm−1, respectively. The measurements performed at different densities show a percent level consistency. This accuracy results from (i) a high baseline stability of the spectra, (ii) an accurate determination of the baseline using argon spectra recorded for the same densities, and (iii) a reliable removal of the local contribution of the absorption lines made easier thanks to subatmospheric pressure recordings. The retrieved binary coefficients are compared to the experimental data included in HITRAN2016 database (Maté et al., 1999, https://doi.org/10.1029/1999JD900824), to the dataset used for Total Carbon Column Observing Network spectra as well as to recent ab initio calculations. Although more accurate, the binary coefficients reported here are found in agreement with the Maté et al. measurements using high pressure Fourier transform spectroscopy. The derived value of the integrated CIA band intensity SO2−air= 1.31(3) × 10−4 cm−2 amagat−2 exceeds the corresponding Fourier transform spectroscopy value by about 3%.

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Section: Introductionmentioning

confidence: 99%

Accurate Laboratory Measurement of the O₂ Collision‐Induced Absorption Band Near 1.27 μm

2019

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“…Mondelain et al, (2013Mondelain et al, ( , 2014 presented observations of the near-IR self-continuum in the 1.6 and 2.1 μm windows at room temperature and above using a cavity ring-down spectrometer (CRDS). Newer measurements (Lechevallier et al, 2018;Richard et al, 2017)…”

Section: 1: Self-continuummentioning

confidence: 99%

Atmospheric observations of the water vapour continuum in the near-infrared windows between 2500–6600 cm<sup>−1</sup>

Elsey¹,

Coleman²,

Gardiner³

et al. 2019

Preprint

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Abstract. Water vapour continuum absorption is potentially important for both closure of the Earth’s energy budget and remote sensing applications. Currently, there are significant uncertainties in its characteristics in the near-infrared atmospheric windows at 2.1 and 1.6 μm. There have been several attempts to measure the continuum in the laboratory; not only are there significant differences amongst these measurements but there are also difficulties in extrapolating the laboratory data taken at room temperature or higher to atmospheric temperatures. Validation is therefore required using field observations of the real atmosphere. There are currently few published observations in atmospheric conditions with enough water vapour to detect a continuum signal within these windows, or where the self-continuum component is significant. We present observations of the near-infrared water vapour continuum from Camborne, UK at sea level using a sun-pointing, radiometrically-calibrated Fourier transform spectrometer in the window regions between 2000–10000 cm−1. Analysis of this data is challenging, particularly because of the need to remove aerosol extinction, and the large uncertainties associated with such field measurements. Nevertheless, we present data that is consistent with recent laboratory datasets in the 4 and 2.1 μm windows (when extrapolated to atmospheric temperatures). These results indicate that the most recent revision (3.2) of the MT_CKD foreign continuum, versions of which are widely used in atmospheric radiation models, requires strengthening by a factor of ~ 5 in the centre of the 2.1 µm window. In the higher-wavenumber window at 1.6 µm, our estimated self and foreign continua are significantly stronger than MT_CKD. The possible contribution of the self and foreign continua to our derived total continuum optical depth is estimated by using laboratory or MT_CKD values of one, to estimate the other. The obtained self-continuum shows some consistency with temperature-extrapolated laboratory data in the centres of the 4 and 2.1 µm windows. The 1.6 μm region is more sensitive to atmospheric aerosol and continuum retrievals and therefore more uncertain than the more robust results at 2.1 and 4 μm. We highlight the difficulties in observing the atmospheric continuum and make the case for additional measurements from both the laboratory and field, with discussion of the requirements for any new field campaign.

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“…Thus, currently there is no consensus on the strength of the MT_CKD 2.5 continuum in some near-IR windows. A good number of measurements in the near-IR have pointed out that the MT_CKD 2.5 continuum may be underestimating the strength of the water vapour continuum in some spectral windows (e.g., Ptashnik et al, 2011Ptashnik et al, , 2012Baranov and Lafferty, 2012;Mondelain et al, 2013;Campargue et al, 2016;Reichert and Sussmann, 2016;Lechevallier et al, 2018). Although these measurements do not agree on how big this underestimation is, the differences are more important for remote sensing techniques that use these windows for retrieval.…”

Section: Introductionmentioning

confidence: 99%

“…It should be noted that the MT_CKD also includes the continua model of several gases such as CO 2 , O 3 and O 2 . There have been unofficial updates of the MT_CKD 2.5 continuum (Lechevallier et al, 2018;O'Dell et al, 2018), but these revisions have not been carried out using adequate experimental constraints. Thus, currently there is no consensus on the strength of the MT_CKD 2.5 continuum in some near-IR windows.…”

Section: Introductionmentioning

confidence: 99%

“…Unlike most of the reported near-IR measurements, which were mostly dedicated to validating the MT_CKD continuum model (see, for example, Lechevallier et al, 2018, and references therein), Ptashnik et al (2011Ptashnik et al ( , 2012 used high-resolution laboratory measurements to derive the CAVIAR (Continuum Absorption at Visible and Infrared Wavelengths and its Atmospheric Relevance) water vapour continuum model that can be used at all wavelengths in the near-IR. The CAVIAR continuum is significantly stronger than the MT_CKD 2.5 continuum in most windows of this spectral region.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity of near‐infrared transmittance calculations for remote sensing applications to recent changes in spectroscopic information

Menang¹

2019

Atmospheric Science Letters

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An accurate determination of atmospheric transmittance relies greatly on the quality of both absorption line parameters and continuum absorption model. A line‐by‐line radiative transfer model has been used to determine the magnitude of the changes in atmospheric transmittance due to recent updates of HITRAN (HIgh‐resolution TRANsmission) line parameters and differences in water vapour continuum formulation. The radiative transfer calculations were carried out at two narrow near‐infrared carbon dioxide bands near 4,854 cm−1 (2.06 μm) and 6,211 cm−1 (1.61 μm), which are currently used by satellite‐based instruments for retrieval of atmospheric CO2 concentrations. Transmittance calculations using line parameters from the last three HITRAN editions (2008, 2012 and 2016) show that HITRAN2016 is more similar to HITRAN2012 than HITRAN2008. However, differences of up to about 5% were obtained between transmittances computed using HITRAN2016 and HITRAN2012. Considering the fact that some groups still use HITRAN2012 in forward models for very high (sub percent) accuracy retrievals of CO2 from satellite measurements, these differences are significant and should be accounted for in the uncertainty budget. Transmittances calculated using the semi‐empirical MT_CKD 2.5 (Mlawer–Tobin–Clough–Kneizys–Davies) and the laboratory‐measured CAVIAR (Continuum Absorption at Visible and Infrared Wavelengths and its Atmospheric Relevance) water vapour continuum models differ by up to about 5–6%. The impact of the continuum formulation adopted for near‐infrared transmittance calculations needs to be quantitatively assessed, most especially as the strength of the water vapour continuum in this spectral region is still contested.

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The water vapour self-continuum absorption in the infrared atmospheric windows: new laser measurements near 3.3 and 2.0 µm

Cited by 39 publications

References 60 publications

Accurate Laboratory Measurement of the O₂ Collision‐Induced Absorption Band Near 1.27 μm

Accurate Laboratory Measurement of the O₂ Collision‐Induced Absorption Band Near 1.27 μm

Atmospheric observations of the water vapour continuum in the near-infrared windows between 2500–6600 cm<sup>−1</sup>

Sensitivity of near‐infrared transmittance calculations for remote sensing applications to recent changes in spectroscopic information

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The water vapour self-continuum absorption in the infrared atmospheric windows: new laser measurements near 3.3 and 2.0 µm

Cited by 39 publications

References 60 publications

Accurate Laboratory Measurement of the O2 Collision‐Induced Absorption Band Near 1.27 μm

Accurate Laboratory Measurement of the O2 Collision‐Induced Absorption Band Near 1.27 μm

Atmospheric observations of the water vapour continuum in the near-infrared windows between 2500–6600 cm&lt;sup&gt;−1&lt;/sup&gt;

Sensitivity of near‐infrared transmittance calculations for remote sensing applications to recent changes in spectroscopic information

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The water vapour self-continuum absorption in the infrared atmospheric windows: new laser measurements near 3.3 and 2.0 µm

Accurate Laboratory Measurement of the O₂ Collision‐Induced Absorption Band Near 1.27 μm

Accurate Laboratory Measurement of the O₂ Collision‐Induced Absorption Band Near 1.27 μm

Atmospheric observations of the water vapour continuum in the near-infrared windows between 2500–6600 cm<sup>−1</sup>