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| Titel |
Simultaneous gas-phase and total water detection for airborne applications with a multi-channel TDL spectrometer at 1.4 μ;m and 2.6 μm |
| VerfasserIn |
Bernhard Buchholz, Armin Afchine, Alexander Klein, Jochen Barthel, Sören Kallweit, Tim Klostermann, Martina Krämer, Cornelius Schiller, Volker Ebert |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078486
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| Zusammenfassung |
| Water vapor measurements especially within clouds are difficult, in particular due to
numerous instrument-specific limitations in precision, time resolution and accuracy. Notably
the quantification of the ice and gas-phase water content in cirrus clouds, which play an
important role in the global climate system, require new high-speed hygrometers concepts
which are capable of resolving large water vapor gradients. Previously we demonstrated a
stationary concept of a Tunable Diode Laser Absorption Spectroscopy (TDLAS)-based
quantification of the ice/liquid water by independent, but simultaneous measurements of A)
the gas-phase water in an open-path configuration (optical-path 125 m) and B) the total
water in an extractive version with a closed cell (30 m path) after evaporating the
condensed water [1]. In this case we used laboratory TDLAS instrumentation in
combination with a long absorption paths and applied those to the AIDA cloud camber
[2].
Recently we developed an advanced, miniature version of the concept, suitable for mobile
field applications and in particular for use on aircrafts. First tests of our new, fiber-coupled
open-path TDLAS cell [3] for airborne applications were combined with the experiences of
our extractive SEALDH instruments [4] and led to a new, multi-channel, “multi-phase
TDL-hygrometer” called “HAI” (“Hygrometer for Atmospheric Investigations”). HAI, which
is explicitly designed for the new German HALO (High Altitude and Long Range Research
Aircraft) airplane, provides a similar, but improved functionality like the stationary,
multi-phase TDLAS developed for AIDA. However HAI comes in a much more
compact, six height units, 30 kg, electronics rack for the main unit and with a new,
completely fiber-coupled, compact, 21 kg, dual-wavelength open-path TDL-cell which is
placed in the aircraft’s skin. HAI is much more complex and versatile than the
AIDA precursor and can be seen as comprised of four TDL-spectrometers, as it
simultaneously measures with two independent wavelengths (1.4 μm for troposphere
and 2.6 μm for UT/LS to permit full coverage of water vapor concentrations from
ground level to the stratosphere) both of which are applied to two measurement
scenarios: A) in two independent extractive, closed cells (1.5 m path, 300 ccm
cell volume) for redundant total water measurements at 1.4 and 2.6 μm and B)
in a dual-wavelength open path cell (4.3 m path length) for a selective gas phase
water detection. All HAI channels, but the 2.6 μm closed cell, are fibred-coupled.
Depending on the sampling inlet (forward direction, ram pressure borrowed) we
achieve in the closed cells a flow of 7 slm at 120 hPa which leads with a bulk flow
assumption to a gas exchange time of 0.3 sec. Both lasers are synchronized and
wavelength tuned at repetition frequencies of up to 1 kHz depending on the spatial
resolution needed. HAI runs autonomous [5] allowing almost maintenance-free
operation even in harsh environments. HAI is further combined with our long-term
experience in TDLAS data evaluation [6] especially in rapidly changing and disturbed
processes [7], [8] which leads to a highly precise, long term stable, fast, accurate,
calibration-free, interference resistant hygrometer which can help to clarify several
important issues - both from a technical perspective (e.g. influence of sampling
system) as well as from a scientific view (e.g. determination ice-content of cirrus
clouds).
In the presentation we will discuss HAI’s novel setup, its performance during the first
tests, and show results from the first successful flights on HALO during the TACTS and
EMSVAL campaigns in 2012.
The HAI development was funded by DFG within the HALO-SPP 1294 and via internal
funds from FZJ.
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[1] B. J. Murray, T. W. Wilson, S. Dobbie, Z. Cui, S. M. R. K. Al-Jumur, O.
Möhler, M. Schnaiter, R. Wagner, S. Benz, M. Niemand, H. Saathoff, V. Ebert,
S. Wagner, and B. Kärcher, “Heterogeneous nucleation of ice particles on glassy
aerosols under cirrus conditions,” Nature Geoscience, vol. 3, no. 4, pp. 233–237, Mar.
2010.
[2] V. Ebert, C. Lauer, H. Saathoff, S. Hunsmann, and S. Wagner, “Simultaneous,
absolute gas-phase and total water detection during cloud formation studies in the AIDA
chamber using a dual 1.37 μm TDL-Spectrometer,” Geophysical Research Abstracts, vol. 10,
pp. 1–2, 2008.
[3] T. Klostermann, Entwicklung und Erprobung des Hygrometer for Atmospheric
Investigations, PhD Thesis, Universität Wuppertal, 2011, p. 118
[4] B. Buchholz, B. Kühnreich, H. G. J. Smit, and V. Ebert, “Validation of an extractive,
airborne, compact TDL spectrometer for atmospheric humidity sensing by blind
intercomparison,” Applied Physics B, Sep. 2012. DOI: 10.1007/s00340-012-5143-1
[5] B. Buchholz, “Neue Hard- und Softwareentwicklungen für autonome, kompakte und
leichte Feld-Diodenlaserspektrometer,” Diploma thesis, Universität Heidelberg,
2010.
[6] V. Ebert and J. Wolfrum, “Absorption spectroscopy,” in OPTICAL
MEASUREMENTS-Techniques and Applications, ed. F. Mayinger, Springer, 1994, pp.
273–312.
[7] C. Schulz, A. Dreizler, V. Ebert, and J. Wolfrum, “Combustion Diagnostics,” in
Handbook of Experimental Fluid Mechanics, C. Tropea, A. L. Yarin, and J. F. Foss, Eds.
Heidelberg: Springer Berlin Heidelberg, 2007, pp. 1241–1316.
[8] V. Ebert, T. Fernholz, C. Giesemann, H. Pitz, H. Teichert, J. Wolfrum, and H.
Jaritz, “Simultaneous diode-laser-based in situ detection of multiple species and
temperature in a gas-fired power plant,” Proc. Combust. Inst., 28, 1, pp. 423–430, 2000. |
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