Swiss H2O Hub
Despite its essential role for the Earth's radiative balance, upper air water vapor (H2O) is still lacking accurate, in-situ, and continuous monitoring. Especially, in the upper troposphere-lower stratosphere (UTLS), between 8–25 km altitudes, performing accurate measurements of H2O is notoriously difficult, due to its very low abundance in this region. To address this long-standing challenge, we developed ALBATROSS, a lightweight (< 3.5 kg) mid-IR laser absorption spectrometer for balloon-borne measurements of upper air H2O.
Figure 1: Picture of the full spectrometer in flight configuration
Figure 2: Schematics of the optical setup. (adapted from: Graf et al., 2021).
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ALBATROSS incorporates a segmented-circular multipass cell (SC-MPC) that was specifically developed to meet the stringent requirements posed by the harsh environmental conditions of the UTLS. The validity of this approach is confirmed by several successful test flights, up to 30 km altitude, conducted from the meteorological observatories of Lindenberg, Germany (Deutscher Wetterdienst) and Payerne, Switzerland (MeteoSwiss). Within the GCOS-CH ALBATROSS project, we assessed the accuracy and precision of the spectrometer at UTLS-relevant conditions using SI-traceable reference gases, in collaboration with the Swiss Federal Institute of Metrology (METAS).The findings of this study demonstrate the unprecedented performances of ALBATROSS for a lightweight hygrometer, as well the importance of including further molecular parameters beyond the standard Voigt-profile model, widely used for spectral fitting of absorption data (Brunamonti et al., 2023). |
Furthermore, the spectrometer also participated in the AquaVIT-4 International Intercomparison of Atmospheric Hygrometers, held at the AIDA climate chamber (Karlsruhe Institute of Technology, Germany). ALBATROSS participates in the GAW/GCOS-CH Swiss H2O Hub project, a field intercomparison of in-situ and remote sensing measurements of UTLS H2O, in collaboration with ETH Zürich, University of Bern and MeteoSwiss. The results of this project will allow characterizing the performances of the spectrometer under real atmospheric conditions, as well as to investigate interannual variability and trends in UTLS H2O over Switzerland. |
ALBATROSS deployment in a balloon flight within the Swiss H2O Hub project at the MeteoSwiss Observatory Payerne, Switzerland. (17 August 2023).
ASPIRE
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The isotopic composition of water vapor can provide important information about the hydrological histories of air masses and as such it is a valuable means for tracing physical processes in hydrological and climatic studies. Despite the large potential of water vapor isotope measurements, the availability of in-situ airborne data is unfortunately very limited. This is mainly due to the lack of adequate analytical tools that allow for accurate and reliable measurements of water vapor isotopes in the upper atmosphere. Laser absorption spectroscopy in the mid-infrared is a rapidly evolving technique that combines very high selectivity, sensitivity with fast time response. In the framework of this project, we propose to develop a compact quantum cascade laser based instrument for measuring the atmospheric water vapor isotopes (HDO and H218O) in the upper atmosphere. |
Our aim is to explore new limits for sensitivity and precision, and to show the feasibility of airborne H2O isotope measurements by laser absorption spectroscopy. The ultimate goal is to provide an easy-to-deploy tool for measuring water vapor isotopes with high temporal resolution and SI-traceable accuracy, and to demonstrate its capabilities under flight conditions, thereby bridging the gap between ground-based point measurements and satellite observations. |
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Graf, M. et al., Compact and lightweight mid-infrared laser spectrometer for balloon-borne water vapor measurements in the UTLS, Atmos. Meas. Tech., 14, 1365–1378 (2021).
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Brunamonti, S. et al., SI-traceable validation of a laser spectrometer for balloon-borne measurements of water vapor in the upper atmosphere, Atmos. Meas. Tech., 16, 4391–4407 (2023).
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