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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/amt-2020-243
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-243
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Jun 2020

Submitted as: research article | 25 Jun 2020

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This preprint is currently under review for the journal AMT.

Compact and Lightweight Mid-IR Laser Spectrometer for Balloon-borne Water Vapor Measurements in the UTLS

Manuel Graf1,3, Philipp Scheidegger1,2, André Kupferschmid2, Herbert Looser1, Thomas Peter3, Ruud Dirksen4, Lukas Emmenegger1, and Béla Tuzson1 Manuel Graf et al.
  • 1Laboratory for Air Pollution/Environmental Technology, Empa - Swiss Federal Laboratory for Materials Science and Technology, 8600 Dübendorf, Switzerland
  • 2Transport at Nanoscale Interfaces, Empa - Swiss Federal Laboratory for Materials Science and Technology, 8600 Dübendorf, Switzerland
  • 3Institute for Atmospheric and Climate Science, ETH Zürich, 8092 Zürich, Switzerland
  • 4Deutscher Wetterdienst (DWD)/GCOS Reference Upper Air Network (GRUAN) Lead Center, Lindenberg, Germany

Abstract. We describe the development, characterization and first field deployments of a quantum cascade laser direct absorption spectrometer (QCLAS) for water vapor measurements in the upper troposphere and lower stratosphere. The instrument is sufficiently small (30×23×11 cm3) and lightweight (3.9 kg) to be carried by meteorological balloons and used for frequent soundings in the upper troposphere and lower stratosphere (UTLS). The spectrometer is a fully independent system, operating autonomously for the duration of a balloon flight. To achieve the required robustness, while satisfying stringent mass limitations, the concepts for optics and electronics have been fundamentally reconsidered compared to laboratory-based spectrometers. A significant enhancement of the mechanical and optical stability is achieved by integrating a segmented circular multipass cell. The H2O mixing ratio is retrieved by calibration-free evaluation of the spectral data, i.e., only relying on SI-traceable measurements and absorption line parameters. An open-path design reduces the risk of contamination, allows fast response and thus high vertical resolution. Laboratory-based characterization experiments show an agreement within 2 % to reference measurements and a precision of 0.1 % under conditions comparable to the UTLS. The instrument successfully performed two balloon-borne test flights up to 28 km altitude. In the troposphere, the retrieved spectroscopic data was in excellent agreement with the parallel measurements by a frost point hygrometer (CFH). At higher altitude, the quality of the spectral data remained unchanged, but outgassed water vapor within the instrument enclosure was reducing the accuracy of the retrieved water vapor data. Despite this limitation, these test flights demonstrated the successful deployment of a laser spectrometer in the UTLS aboard a low-volume meteorological balloon, with the perspective of future highly resolved, accurate and cost-efficient soundings.

Manuel Graf et al.

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Latest update: 10 Jul 2020
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Short summary
Water vapor is the most important natural greenhouse gas. However, the accurate and frequent measurement of its abundance, especially in the upper troposphere and lower stratosphere (UTLS), is technically challenging. We developed and characterized a mid-IR absorption spectrometer for highly accurate water vapor measurements in the UTLS. The instrument is sufficiently small and lightweight (3.9 kg) to be carried by meteorological balloons, which enables frequent and cost-effective soundings.
Water vapor is the most important natural greenhouse gas. However, the accurate and frequent...
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