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 (UTLS). The instrument is sufficiently small ($\mathrm{30}\times \mathrm{23}\times \mathrm{11}$ cm³) and lightweight (3.9 kg) to be carried by meteorological balloons and used for frequent soundings in the 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 newly designed segmented circular multipass cell which allows for 6 m optical path length in a very compact fashion. The H₂O volume mixing ratio is retrieved by calibration-free evaluation of the spectral data, i.e., only relying on SI-traceable measurements and absorption line parameters. The open-path design reduces the risk of contamination and allows for fast response and thus high vertical resolution. Laboratory-based characterization experiments show an agreement within 2 % of 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 show an excellent agreement with the accompanying 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 hindering an accurate measurement of the atmospheric water vapor. Despite this limitation, these test flights demonstrated the operation of a compact laser spectrometer in the UTLS aboard a low-volume meteorological balloon, opening the perspective for future highly resolved, accurate, and cost-efficient soundings.

中文翻译：

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紧凑轻巧的中红外激光光谱仪，用于在UTLS中测量气球中的水蒸气

我们描述了一种量子级联激光直接吸收光谱仪（QCLAS）的开发，表征和首次现场部署，该光谱仪用于对流层上层和平流层下层（UTLS）中的水蒸气测量。仪器足够小（$\mathrm{30}\times \mathrm{23}\times \mathrm{11}$ cm ³）和重量轻（3.9  kg），由气象气球携带，用于UTLS中的频繁发声。光谱仪是一个完全独立的系统，在气球飞行期间会自动运行。为了达到所需的耐用性，同时满足严格的质量限制，与基于实验室的光谱仪相比，从根本上重新考虑了光学和电子学的概念。通过集成新设计的分段圆形多通道单元，可以显着提高机械和光学稳定性，该单元可以以非常紧凑的方式实现6  m的光程长度。的ħ ₂ ö通过对光谱数据进行无标定评估即可获得体积混合比，即仅依赖于SI可追踪的测量值和吸收谱线参数。开放路径设计降低了污染的风险，并允许快速响应，因此具有很高的垂直分辨率。基于实验室的表征实验表明，在与UTLS相当的条件下，参考测量值的一致性在2％以内，精度为0.1％。该仪器成功进行了两次气球飞行测试，飞行距离达28 公里高度。在对流层中，检索到的光谱数据与霜点湿度计（CFH）的伴随测量值显示出极好的一致性。在更高的海拔上，光谱数据的质量保持不变，但是仪器外壳内的水蒸气逸出妨碍了对大气水蒸气的准确测量。尽管有这些限制，但这些测试飞行还是证明了UTLS紧凑型激光光谱仪在小容量气象气球上的运行，为将来获得高度解析，准确且经济高效的探测技术打开了视野。