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| Titel |
Rapid, optical measurement of the atmospheric pressure on a fast research aircraft using open-path TDLAS |
| VerfasserIn |
B. Buchholz, A. Afchine, V. Ebert |
| 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 ; 7, no. 11 ; Nr. 7, no. 11 (2014-11-06), S.3653-3666 |
| Datensatznummer |
250115942
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| Publikation (Nr.) |
 copernicus.org/amt-7-3653-2014.pdf |
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| Zusammenfassung |
Because of the high travel speed, the complex flow dynamics around
an aircraft, and the complex dependency of the fluid dynamics on
numerous airborne parameters, it is quite difficult to obtain
accurate pressure values at a specific instrument location of an
aircraft's fuselage. Complex simulations using computational fluid
dynamics (CFD) models can in theory computationally "transfer"
pressure values from one location to another. However, for long
flight patterns, this process is inconvenient and
cumbersome. Furthermore, these CFD transfer models require a local
experimental validation, which is rarely available.
In this paper, we describe an integrated approach for
a spectroscopic, calibration-free, in-flight pressure determination
in an open-path White cell on an aircraft fuselage using ambient,
atmospheric water vapour as the "sensor species". The presented
measurements are realised with the HAI (Hygrometer for Atmospheric
Investigations) instrument, built for multiphase water detection via
calibration-free TDLAS (tunable diode laser absorption
spectroscopy). The pressure determination is based on raw data used
for H2O concentration measurement, but with a different
post-flight evaluation method, and can therefore be conducted at
deferred time intervals on any desired flight track.
The spectroscopic pressure is compared in-flight with the static
ambient pressure of the aircraft avionic system and
a micro-mechanical pressure sensor, located next to the open-path
cell, over a pressure range from 150 to 800 hPa,
and a water vapour concentration range of more than 3 orders of
magnitude. The correlation between the micro-mechanical pressure sensor measurements and the spectroscopic pressure
measurements shows an average deviation from linearity of only
0.14% and a small offset of 9.5 hPa. For the
spectroscopic pressure evaluation we derive measurement uncertainties
under laboratory conditions of 3.2 and 5.1% during in-flight operation on the HALO airplane. Under certain flight
conditions we quantified, for the first time, stalling-induced,
dynamic pressure deviations of up to 30% (at 200 hPa)
between the avionic sensor and the optical and mechanical pressure
sensors integrated in HAI. Such severe local pressure deviations
from the typically used avionic pressure are important to take into
account for other airborne sensors employed on such fast flying
platforms as the HALO aircraft. |
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