A two-channel, tunable diode laser-based hygrometer for measurement of water vapor and cirrus cloud ice water content in the upper troposphere and lower stratosphere

Abstract

Abstract. The recently developed NOAA Water instrument is a two-channel, closed-path, tunable diode laser absorption spectrometer designed for the measurement of upper troposphere/lower stratosphere water vapor and enhanced total water (vapor + inertially enhanced condensed phase) from the NASA Global Hawk unmanned aircraft system (UAS) or other high-altitude research aircraft. The instrument utilizes wavelength-modulated spectroscopy with second harmonic detection near 2694 nm to achieve high precision with a 79 cm double-pass optical path. The detection cells are operated under constant temperature, pressure, and flow conditions to maintain a constant sensitivity to H2O independent of the ambient sampling environment. An onboard calibration system is used to perform periodic in situ calibrations to verify the stability of the instrument sensitivity during flight. For the water vapor channel, ambient air is sampled perpendicular to the flow past the aircraft in order to reject cloud particles, while the total water channel uses a heated, forward-facing inlet to sample both water vapor and cloud particles. The total water inlet operates subisokinetically, thereby inertially enhancing cloud particle number in the sample flow and affording increased cloud water content sensitivity. The NOAA Water instrument was flown for the first time during the second deployment of the Airborne Tropical TRopopause EXperiment (ATTREX) in February–March 2013 on the NASA Global Hawk UAS. The instrument demonstrated a typical in-flight precision (1 s, 1σ) of better than 0.17 parts per million (ppm, 10−6 mol mol−1), with an overall H2O vapor measurement uncertainty of 5% ± 0.23 ppm. The inertial enhancement for cirrus cloud particle sampling under ATTREX flight conditions ranged from 33 to 48 for ice particles larger than 8 μm in diameter, depending primarily on aircraft altitude. The resulting ice water content detection limit (2σ) was 0.023–0.013 ppm, corresponding to approximately 2 μg m−3, with an estimated overall uncertainty of 20%.

Atmospheric Sampling on Ascension Island Using Multirotor UAVs

“…In particular, significant traction is being realised in the areas of remote sensing [10,11], mapping 2D/3D structures [12,13,14] and atmospheric sampling [15,16,17,18,19,20,21,22,23,24,25] using a range of emerging sensor technologies [26,27,28,29]. However, most applications to date that have been used for atmospheric sampling have been at lower altitudes in the 500 m–1000 m range [15,19] or involve longer range fixed wing platforms that often require considerable resources to deploy [30,31,32].…”

HAI, a new airborne, absolute, twin dual-channel, multi-phase TDLAS-hygrometer: background, design, setup, and first flight data

“…These capabilities were, for example, extensively demonstrated via measurements inside of combustion processes in industrial power plants (Ebert et al, 2000a;Schlosser et al, 2002;Sun et al, 2013;Teichert et al, 2003). TDLAS, especially in the near infrared spectral range, is a powerful as well as versatile diagnostic technique and has led to numerous applications in atmospheric hygrometry (Diskin et al, 2002;Fahey and Gao, 2009;Gurlit et al, 2005;May, 1998;Schiff et al, 1994;Thornberry et al, 2015). Advantageous properties of diode lasers are very high spectral resolution (providing excellent chemical selectivity), high power density, and continuous wavelength tunability in combination with interesting technical features such as low cost, very low size/weight/power consumption, long lifetime, excellent beam quality, and optical fiber coupling to name just a few.…”

“…A high number of (mostly single channel and single H 2 O phase) hygrometers have been developed in the last decades with various advantages and drawbacks (Wiederhold, 1997). A non-exhaustive selection of instruments has been described (Buck, 1985;Busen and Buck, 1995;Cerni, 1994;Desjardins et al, 1989;Diskin et al, 2002;Durry et al, 2008;Ebert et al, 2000b;Gurlit et al, 2005;Hansford et al, 2006;Helten et al, 1998;Hunsmann et al, 2008;Karpechko et al, 2014;Kley and Stone, 1978;May, 1998;Meyer et al, 2015;Ohtaki and Matsui, 1982;Roths and Busen, 1996;Salasmaa and Kostamo, 1986;Sargent et al, 2013;Schiff et al, 1994;Silver and Hovde, 1994b, a;Thornberry et al, 2015;Webster et al, 2004;Zöger et al, 1999a, b;Zondlo et al, 2010). Consequently, the question should be raised from the opposite point of view: What are the important and required properties to be covered and combined for the near-universal Hygrometer for Atmospheric Investigation (HAI) to serve as an innovative and cutting-edge tool to explore open and new scientific questions related to atmospheric water vapor?…”

A laser-induced fluorescence instrument for aircraft measurements of sulfur dioxide in the upper troposphere and lower stratosphere

“…The SO 2 instrument operated successfully during seven flights from 20 to 30 October up to 19.4 km altitude. In addition to the SO 2 measurements, the in situ payload included instruments for measuring O 3 (Gao et al, 2012), water vapor and ice water content (Thornberry et al, 2015), meteorological parameters (Scott et al, 1990) and tracers (Heidt et al, 1989), thereby providing a valuable payload for investigating aspects of the UT-LS sulfur budget.…”