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| Titel |
Fast, multi-phase H2O measurements on board of HALO: Results from the novel HAI instrument during the first field campaigns. |
| VerfasserIn |
Bernhard Buchholz, Armin Afchine, Martina Krämer, Volker Ebert |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093984
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| Publikation (Nr.) |
 EGU/EGU2014-9241.pdf |
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| Zusammenfassung |
| Water vapor is a key species for many questions in atmospheric research [1] [2]
but is also a gas species which is complex to handle. A particular challenge is the
simultaneous quantification of gas and condensed phase water. This is especially
true for measurements on airborne platforms but also for laboratory experiments
[3]. On research aircraft, total water measurement (i.e. the sum of gas-phase and
ice-phase) is realized by sampling air with an inlet faced into flight direction (“forward”
sampling) and subsequent evaporation of the ice crystals in the heated sampling
lines. Gas-phase detection is typically realized using inlets facing against flight
direction (“backward” sampling) or “Rosemount” inlets where an air stream is sampled
perpendicular to the high speed airflow through the inlet. For both methods it is believed
that no ice crystals reach the downstream hygrometer, but the question remains
-especially for Rosemount inlets- if some small ice particles or water droplets may have
entered the sampling lines. In addition to the question of proper sampling of the
water phases, currently no hygrometer exists that measures all phases with the same
measurement principle in one instrument. In the rare occasions that multi-phase
measurements are realized, gas-and condensed-phase observations rely on different
methods and calibration strategies so that precision and accuracy levels are difficult to
compare.
The novel HAI (Hygrometer for Atmospheric Investigation) realizes a simultaneous
multi-phase hygrometer in a unique concept [4]. Water detection with HAI is based on
Tunable Diode Laser Absorption Spectroscopy (TDLAS) with a special evaluation method
allowing absolute water vapor measurements without any sensor calibration [5].
The HAI instrument contains two independent dual-channel spectrometers, one at
1.4μm and one at 2.6μm which allows to cover a very wide water concentration
range from 1 to 30000ppmv. Both HAI spectrometers couple one light path in a
so called "closed-path" cell [6] for total water measurement via a forward facing
inlet. The other part of the laser light is coupled to an "open-path" cell [7] placed
outside of the aircraft fuselage to measure gas phase water without any possible
artifacts from ice or liquid particles. The frequency of the measurements can be up to
240Hz (4.2msec) for all four channels. Altogether, the novel HAI instrument
allows fast, accurate and precise dual-phase water measurements. The individual
evaluation of the multi-channel raw-data is done afterwards, without any channel
interdependencies, in a calibration-free mode. The water signals are combined with an
extensive set of more than 100 housekeeping data to enable a holistic data quality
management and a rigorous signal scrutiny to maximize the confidence level of the final
H2O values. HAI therefore represents a new unique research tool for atmospheric
hygrometry to address numerous open topics in atmospheric research. First scientific HAI
campaigns have been successfully realized in 2012 onboard the German research plane
HALO (High Altitude and Long Range Research Aircraft) during the TACTS and
ESMVal missions. The first two HALO campaigns in clouds (MLCIRRUS and
ACRIDICON) will be realized in 2014. In our contribution we present and discuss the
performance of HAI and show detailed evaluations of typical inflight data. The
results of the first two HAI campaigns on HALO resulted in more than 100 operation
hours of continuous data and show nice agreement between the closed-path and
open-path under clear sky conditions, despite the different sampling conditions of
the sensor channels and airspeed of up to 900km/h in the open path section. All
mission data are and will be uploaded to the HALO database and are available for
further scientific exploitation. Furthermore, the HAI principle can be adapted to other
(airborne) platforms and be used for phase resolved science of the atmospheric water
cycle. In parallel HAI’s cal-free data evaluation principle will be validated with
metrological scrutiny to further investigate the possibility of flying field-qualified
metrological transfer standards to resolve the persistent discrepancies in atmospheric
hygrometry.
The HAI development is funded by DFG within the SPP 1294 HALO via FKZ EB
235/3
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doi:10.1126/science.1227004.
[2] S. Sherwood, S. Bony, and J. Dufresne, Nature, vol. 505, no. 7481, pp. 37–42,
(2014),
[3] D. Fahey R. Gao, “Summary of the AquaVIT Water Vapor Intercomparison” source:
https://aquavit.icg.kfa-juelich.de/WhitePaper/AquaVITWhitePaper_Final_23Oct2009_6MB.pdf,
(2009).
[4] V. Ebert, C. Lauer, H. Saathoff, S. Hunsmann, and S. Wagner, Geophys. Res.Abstr.,
10, p. EGU2008-A-10066 (2008).
[5] V. Ebert and J. Wolfrum, “Absorption spectroscopy,” in Optical Measurements -
Techniques and Applications, F. Mayinger and O. Feldmann, Eds., Springer Heidelberg,
München, ISBN:978-3540666905, pp. 273–312, (2000).
[6] B. Buchholz, B. Kühnreich, HGJ. Smit, V. Ebert, Appl. Phys. B, vol. 110, no. 2, pp.
249–262, (2013),
[7] B. Buchholz, A. Afchine, A. Klein, J. Barthel, T. Klostermann, S. Kallweit,
M. Krämer, C. Schiller, and V. Ebert, in DGAO Proceedings, ISSN:1614-8436 –
urn:nbn:de:0287-2013-B035-5, (2013). |
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