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| Titel |
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 |
| VerfasserIn |
T. D. Thornberry, A. W. Rollins, R. S. Gao, L. A. Watts, S. J. Ciciora, R. J. McLaughlin, D. W. Fahey |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 1 ; Nr. 8, no. 1 (2015-01-12), S.211-224 |
| Datensatznummer |
250116048
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| Publikation (Nr.) |
 copernicus.org/amt-8-211-2015.pdf |
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| Zusammenfassung |
| 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%. |
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