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| Titel |
Advances in Fast Response Acoustically Derived Air Temperature Measurements |
| VerfasserIn |
Ivan Bogoev, Larry Jacobsen, Thomas Horst, Benjamin Conrad |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122644
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| Publikation (Nr.) |
 EGU/EGU2016-1735.pdf |
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| Zusammenfassung |
| Fast-response accurate air-temperature measurements are required when estimating turbulent
fluxes of heat, water and carbon dioxide by open-path eddy-covariance technique. In
comparison with contact thermometers like thermocouples, ultra-sonic thermometers do not
suffer from solar radiation loading, water vapor condensation and evaporative cooling effects.
Consequently they have the potential to provide more accurate true air temperature
measurements. The absolute accuracy of the ultrasonic thermometer is limited by the
following parameters: the distance between the transducer pairs, transducer delays associated
with the electrical-acoustic signal conversion that vary with temperature, components of the
wind vector that are normal to the ultrasonic paths, and humidity. The distance
between the transducer pairs is commonly obtained by coordinate measuring machine.
Improved accuracy demonstrated in this study results from increased stiffness in
the anemometer head to better maintain the ultrasonic path-length distances. To
further improve accuracy and account for changes in transducer delays and distance
as a function of temperature, these parameters are characterized in a zero-wind
chamber over the entire operating temperature range. When the sonic anemometer is
combined with a co-located fast-response water vapor analyzer, like in the IRGASON
instrument, speed of sound can be compensated for humidity effects on a point-by-point
basis resulting in a true fast-response air temperature measurement. Laboratory test
results show that when the above steps are implemented in the calibration of the
ultrasonic thermometer air-temperature accuracy better than ±0.5 degrees Celsius can
be achieved over the entire operating range. The approach is also validated in a
field inter-comparison with an aspirated thermistor probe mounted in a radiation
shield. |
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