New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns
<p>Low-level flights over tundra wetlands in Alaska and Canada have been conducted during the Airborne Measurements of Methane Emissions (AirMeth) campaigns to measure turbulent methane fluxes in the atmosphere. In this paper we describe the instrumentation and new calibration procedures fo...
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doaj-a53db22a3b6b49cf9127aadef762bfc72020-11-24T22:25:47ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482018-07-01114567458110.5194/amt-11-4567-2018New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaignsJ. Hartmann0M. Gehrmann1K. Kohnert2S. Metzger3S. Metzger4T. Sachs5Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyGFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, GermanyNational Ecological Observatory Network, Battelle, 1685 38th Street, Boulder, CO 80301, USAUniversity of Wisconsin-Madison, Dept. of Atmospheric and Oceanic Sciences, 1225 West Dayton Street, Madison, WI 53706, USAGFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany<p>Low-level flights over tundra wetlands in Alaska and Canada have been conducted during the Airborne Measurements of Methane Emissions (AirMeth) campaigns to measure turbulent methane fluxes in the atmosphere. In this paper we describe the instrumentation and new calibration procedures for the essential pressure parameters required for turbulence sensing by aircraft that exploit suitable regular measurement flight legs without the need for dedicated calibration patterns. We estimate the accuracy of the mean wind and the turbulence measurements. We show that airborne measurements of turbulent fluxes of methane and carbon dioxide using cavity ring-down spectroscopy trace gas analysers together with established turbulence equipment achieve a relative accuracy similar to that of measurements of sensible heat flux if applied during low-level flights over natural area sources. The inertial subrange of the trace gas fluctuations cannot be resolved due to insufficient high-frequency precision of the analyser, but, since this scatter is uncorrelated with the vertical wind velocity, the covariance and thus the flux are reproduced correctly. In the covariance spectra the −7∕3 drop-off in the inertial subrange can be reproduced if sufficient data are available for averaging. For convective conditions and flight legs of several tens of kilometres we estimate the flux detection limit to be about 4 mg m<sup>−2</sup> d<sup>−1</sup> for <span style="text-decoration: overline;"><i>w</i>′CH<sub>4</sub>′</span>, 1.4 g m<sup>−2</sup> d<sup>−1</sup> for <span style="text-decoration: overline;"><i>w</i>′CO<sub>2</sub>′</span> and 4.2 W m<sup>−2</sup> for the sensible heat flux.</p>https://www.atmos-meas-tech.net/11/4567/2018/amt-11-4567-2018.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
J. Hartmann M. Gehrmann K. Kohnert S. Metzger S. Metzger T. Sachs |
spellingShingle |
J. Hartmann M. Gehrmann K. Kohnert S. Metzger S. Metzger T. Sachs New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns Atmospheric Measurement Techniques |
author_facet |
J. Hartmann M. Gehrmann K. Kohnert S. Metzger S. Metzger T. Sachs |
author_sort |
J. Hartmann |
title |
New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns |
title_short |
New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns |
title_full |
New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns |
title_fullStr |
New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns |
title_full_unstemmed |
New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns |
title_sort |
new calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the airmeth campaigns |
publisher |
Copernicus Publications |
series |
Atmospheric Measurement Techniques |
issn |
1867-1381 1867-8548 |
publishDate |
2018-07-01 |
description |
<p>Low-level flights over tundra wetlands in Alaska and Canada have been
conducted during the Airborne Measurements of Methane Emissions (AirMeth) campaigns to measure turbulent methane fluxes
in the atmosphere. In this paper we describe the instrumentation and new
calibration procedures for the essential pressure parameters required for
turbulence sensing by aircraft that exploit suitable regular measurement
flight legs without the need for dedicated calibration patterns. We estimate
the accuracy of the mean wind and the turbulence measurements. We show that
airborne measurements of turbulent fluxes of methane and carbon dioxide using
cavity ring-down spectroscopy trace gas analysers together with established
turbulence equipment achieve a relative accuracy similar to that of
measurements of sensible heat flux if applied during low-level flights over
natural area sources. The inertial subrange of the trace gas fluctuations
cannot be resolved due to insufficient high-frequency precision of the
analyser, but, since this scatter is uncorrelated with the vertical wind
velocity, the covariance and thus the flux are reproduced correctly. In the
covariance spectra the −7∕3 drop-off in the inertial subrange can be
reproduced if sufficient data are available for averaging. For convective
conditions and flight legs of several tens of kilometres we estimate the flux
detection limit to be about
4 mg m<sup>−2</sup> d<sup>−1</sup> for
<span style="text-decoration: overline;"><i>w</i>′CH<sub>4</sub>′</span>,
1.4 g m<sup>−2</sup> d<sup>−1</sup> for <span style="text-decoration: overline;"><i>w</i>′CO<sub>2</sub>′</span> and
4.2 W m<sup>−2</sup> for the sensible heat flux.</p> |
url |
https://www.atmos-meas-tech.net/11/4567/2018/amt-11-4567-2018.pdf |
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