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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 1 | Copyright
Atmos. Meas. Tech., 11, 459-471, 2018
https://doi.org/10.5194/amt-11-459-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 23 Jan 2018

Research article | 23 Jan 2018

Absolute, pressure-dependent validation of a calibration-free, airborne laser hygrometer transfer standard (SEALDH-II) from 5 to 1200 ppmv using a metrological humidity generator

Bernhard Buchholz1,2,a and Volker Ebert1,2,3 Bernhard Buchholz and Volker Ebert
  • 1Physikalisch-Technische Bundesanstalt Braunschweig, Braunschweig, Germany
  • 2Physikalisch Chemisches Institut, Universität Heidelberg, Heidelberg, Germany
  • 3Center of Smart Interfaces, Technische Universität Darmstadt, Darmstadt, Germany
  • acurrently at: Department of Civil and Environmental Engineering, Princeton University, Princeton, USA

Abstract. Highly accurate water vapor measurements are indispensable for understanding a variety of scientific questions as well as industrial processes. While in metrology water vapor concentrations can be defined, generated, and measured with relative uncertainties in the single percentage range, field-deployable airborne instruments deviate even under quasistatic laboratory conditions up to 10–20%. The novel SEALDH-II hygrometer, a calibration-free, tuneable diode laser spectrometer, bridges this gap by implementing a new holistic concept to achieve higher accuracy levels in the field. We present in this paper the absolute validation of SEALDH-II at a traceable humidity generator during 23 days of permanent operation at 15 different H2O mole fraction levels between 5 and 1200ppmv. At each mole fraction level, we studied the pressure dependence at six different gas pressures between 65 and 950hPa. Further, we describe the setup for this metrological validation, the challenges to overcome when assessing water vapor measurements on a high accuracy level, and the comparison results. With this validation, SEALDH-II is the first airborne, metrologically validated humidity transfer standard which links several scientific airborne and laboratory measurement campaigns to the international metrological water vapor scale.

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This paper describes the absolute validation of the novel, calibration-free SEALDH-II hygrometer at a traceable humidity generator. During 23 days of permanent operation, 15 H2O mole fractions levels (5–1200 ppmv) at 6 gas pressures (65–950 hPa) were validated. With this validation, SEALDH-II is the first metrologically validated humidity transfer standard which links several scientific airborne and laboratory measurement campaigns to the international metrological water vapor scale.
This paper describes the absolute validation of the novel, calibration-free SEALDH-II hygrometer...
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