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The AquaVIT-1 intercomparison of atmospheric water vapor measurement techniques

The AquaVIT-1 intercomparison of atmospheric water vapor measurement techniquesAtmospheric Measurement Techniques, 7, 3177-3213, 2014Author(s): D. W. Fahey, R.-S. Gao, O. Möhler, H. Saathoff, C. Schiller, V. Ebert, M. Krämer, T. Peter, N. Amarouche, L. M. Avallone, R. Bauer, Z. Bozóki, L. E. Christensen, S. M. Davis, G. Durry, C. Dyroff, R. L. Herman, S. Hunsmann, S. M. Khaykin, P. Mackrodt, J. Meyer, J. B. Smith, N. Spelten, R. F. Troy, H. Vömel, S. Wagner, and F. G. WienholdThe AquaVIT-1 intercomparison of atmospheric water vapor measurement
techniques was conducted at the aerosol and cloud simulation chamber AIDA
(Aerosol Interaction and Dynamics in the Atmosphere) at
the Karlsruhe Institute of Technology, Germany, in October 2007. The overall
objective was to intercompare state-of-the-art and prototype atmospheric
hygrometers with each other and with independent humidity standards under
controlled conditions. This activity was conducted as a blind
intercomparison with coordination by selected referees. The effort was
motivated by persistent discrepancies found in atmospheric measurements
involving multiple instruments operating on research aircraft and balloon
platforms, particularly in the upper troposphere and lower stratosphere,
where water vapor reaches its lowest atmospheric values (less than 10 ppm).
With the AIDA chamber volume of 84 m3, multiple instruments analyzed
air with a common water vapor mixing ratio, by extracting air into
instrument flow systems, by locating instruments inside the chamber, or
by sampling the chamber volume optically. The intercomparison was successfully
conducted over 10 days during which pressure, temperature, and mixing ratio
were systematically varied (50 to 500 hPa, 185 to 243 K, and 0.3 to 152 ppm).
In the absence of an accepted reference instrument, the absolute accuracy of
the instruments was not established. To evaluate the intercomparison, the
reference value was taken to be the ensemble mean of a core subset of the
measurements. For these core instruments, the agreement between 10 and
150 ppm of water vapor is considered good with variation about the reference
value of about ±10% (±1σ). In the region of most
interest between 1 and 10 ppm, the core subset agreement is fair with
variation about the reference value of ±20% (±1σ).
The upper limit of precision was also derived for each instrument from the
reported data. The implication for atmospheric measurements is that the
substantially larger differences observed during in-flight intercomparisons
stem from other factors associated with the moving platforms or the
non-laboratory environment. The success of AquaVIT-1 provides a template for
future intercomparison efforts with water vapor or other species that are
focused on improving the analytical quality of atmospheric measurements on
moving platforms.

Atmospheric Measurement Techniques 2014/09/26 - 15:30 Czytaj