An open-path ammonia analyzer for eddy covariance flux measurement

Eddy covariance (EC) systems are being used to measure sensible heat (H) and latent heat (LE) fluxes in order to determine crop water use or evapotranspiration (ET). The reliability of EC measurements depends on meeting certain meteorological assumptions; the most important of such are horizontal homogeneity, stationarity, and non-advective conditions. Over heterogeneous surfaces, the spatial context of the measurement must be known in order to properly interpret the magnitude of the heat flux measurement results. Over the past decades, there has been a proliferation of ‘heat flux source area’ (i.e., footprint) modeling studies, but only a few have explored the accuracy of the models over heterogeneous agricultural land. A composite ET estimate was created by using the estimated footprint weights for an EC system in the upwind corner of four fields and separate ET estimates from each of these fields. Three analytical footprint models were evaluated by comparing the composite ET to the measured ET. All three models performed consistently well, with an average mean bias error (MBE) of about −0.03 mm h−1 (−4.4%) and root mean square error (RMSE) of 0.09 mm h−1 (10.9%). The same three footprint models were then used to adjust the EC-measured ET to account for the fraction of the footprint that extended beyond the field of interest. The effectiveness of the footprint adjustment was determined by comparing the adjusted ET estimates with the lysimetric ET measurements from within the same field. This correction decreased the absolute hourly ET MBE by 8%, and the RMSE by 1%.

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Eddy-covariance flux measurements with a weight-shift microlight aircraft

Atmospheric Measurement Techniques ◽

10.5194/amt-5-1699-2012 ◽

2012 ◽

Vol 5 (7) ◽

pp. 1699-1717 ◽

Cited By ~ 31

Author(s):

S. Metzger ◽

W. Junkermann ◽

M. Mauder ◽

F. Beyrich ◽

K. Butterbach-Bahl ◽

...

Keyword(s):

Heat Flux ◽

Eddy Covariance ◽

Low Cost ◽

Sensible Heat Flux ◽

Flux Measurement ◽

Wind Measurement ◽

Airborne Measurements ◽

Weight Shift ◽

Flux Measurements

Abstract. The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (σu,v ≤ 0.09 m s−1, σw = 0.04 m s−1), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s−1), and sensible- (5 W m−2) and latent (3 W m−2) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform.

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Air-Sea Fluxes of CO<sub>2</sub> and CH<sub>4</sub> from the Penlee Point Atmospheric Observatory on the South West Coast of the UK

10.5194/acp-2015-717 ◽

2016 ◽

Cited By ~ 1

Author(s):

M. Yang ◽

T. G. Bell ◽

F. E. Hopkins ◽

V. Kitidis ◽

P. W. Cazenave ◽

...

Keyword(s):

Eddy Covariance ◽

West Coast ◽

Phytoplankton Bloom ◽

Flux Measurement ◽

Sensible Heat ◽

The South ◽

Eddy Covariance Method ◽

Spring Phytoplankton Bloom ◽

South West ◽

South West Coast

Abstract. We present air-sea fluxes of carbon dioxide (CO2), methane (CH4), momentum, and sensible heat measured by the eddy covariance method from the recently established Penlee Point Atmospheric Observatory (PPAO) on the South West coast of the United Kingdom. Measurements from the southwest direction (background marine air) at three different sampling heights (approximately 15, 18, 27 m above mean sea level, AMSL) in three different periods during 2014–2015 are shown. At sampling heights ≥ 18 m AMSL, measured fluxes of momentum and sensible heat demonstrate reasonable agreement with their expected transfer rates over the open ocean. This confirms the suitability of PPAO for air-sea exchange measurements. We observed reductions in the air-to-sea fluxes of CO2 from spring to summer in both years, which coincided with the breakdown of the spring phytoplankton bloom. At all sampling heights, mean CH4 fluxes were positive, suggesting marine emissions. Higher CH4 fluxes were observed during rising tides (20&pm;3; 29&pm;6; 38&pm;3 μmole m−2 d−1 at 15, 27, 18 m AMSL) than during falling tides (14&pm;2; 21&pm;5; 22&pm;2 μmole m−2 d−1, respectively), consistent with an elevated CH4 source from an estuarine outflow driven by local tidal circulation. Based on observations at PPAO, we also estimate the detection limit of the eddy covariance CH4 flux measurement to be ~20 μmole m−2 d−1 over hourly timescales (~4 μmole m−2 d−1 over 24 hours).

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Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

Atmospheric Measurement Techniques ◽

10.5194/amt-11-6075-2018 ◽

2018 ◽

Vol 11 (11) ◽

pp. 6075-6090 ◽

Cited By ~ 4

Author(s):

Brian J. Butterworth ◽

Brent G. T. Else

Keyword(s):

Carbon Dioxide ◽

Sea Ice ◽

Eddy Covariance ◽

Co2 Flux ◽

Carbon Dioxide Flux ◽

The Arctic ◽

Closed Path ◽

Eddy Covariance Method ◽

Open Path ◽

Flux Measurements

Abstract. The Arctic marine environment plays an important role in the global carbon cycle. However, there remain large uncertainties in how sea ice affects air–sea fluxes of carbon dioxide (CO2), partially due to disagreement between the two main methods (enclosure and eddy covariance) for measuring CO2 flux (FCO2). The enclosure method has appeared to produce more credible FCO2 than eddy covariance (EC), but is not suited for collecting long-term, ecosystem-scale flux datasets in such remote regions. Here we describe the design and performance of an EC system to measure FCO2 over landfast sea ice that addresses the shortcomings of previous EC systems. The system was installed on a 10 m tower on Qikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly 35 km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. The system incorporates recent developments in the field of air–sea gas exchange by measuring atmospheric CO2 using a closed-path infrared gas analyzer (IRGA) with a dried sample airstream, thus avoiding the known water vapor issues associated with using open-path IRGAs in low-flux environments. A description of the methods and the results from 4 months of continuous flux measurements from May through August 2017 are presented, highlighting the winter to summer transition from ice cover to open water. We show that the dried, closed-path EC system greatly reduces the magnitude of measured FCO2 compared to simultaneous open-path EC measurements, and for the first time reconciles EC and enclosure flux measurements over sea ice. This novel EC installation is capable of operating year-round on solar and wind power, and therefore promises to deliver new insights into the magnitude of CO2 fluxes and their driving processes through the annual sea ice cycle.

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The eddy-covariance storage term in air: Consistent community resources improve flux measurement reliability

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2019.107734 ◽

2019 ◽

Vol 279 ◽

pp. 107734 ◽

Cited By ~ 3

Author(s):

Ke Xu ◽

Natchaya Pingintha-Durden ◽

Hongyan Luo ◽

David Durden ◽

Cove Sturtevant ◽

...

Keyword(s):

Eddy Covariance ◽

Flux Measurement ◽

Community Resources ◽

Measurement Reliability ◽

Storage Term

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Open-path eddy covariance measurements of ammonia fluxes from a beef cattle feedlot

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2015.06.007 ◽

2015 ◽

Vol 213 ◽

pp. 193-202 ◽

Cited By ~ 30

Author(s):

Kang Sun ◽

Lei Tao ◽

David J. Miller ◽

Mark A. Zondlo ◽

Kira B. Shonkwiler ◽

...

Keyword(s):

Beef Cattle ◽

Eddy Covariance ◽

Open Path ◽

Eddy Covariance Measurements ◽

Cattle Feedlot

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New Open-Path Low-Power Standardized Automated CO2/H2O Flux Measurement System: Concentrations, Co-spectra and Fluxes Comparison with Established Models

10.1002/essoar.926720855ddc2178.bf18b4167b5a4266.1 ◽

2018 ◽

Author(s):

George Burba ◽

Israel Begashaw ◽

James Kathilankal

Keyword(s):

Low Power ◽

Measurement System ◽

Flux Measurement ◽

Open Path

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Performance Evaluation of an Integrated Open-Path Eddy Covariance System in a Cold Desert Environment

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-15-0149.1 ◽

2016 ◽

Vol 33 (11) ◽

pp. 2385-2399 ◽

Cited By ~ 9

Author(s):

Wei Wang ◽

Jiaping Xu ◽

Yunqiu Gao ◽

Ivan Bogoev ◽

Jian Cui ◽

...

Keyword(s):

Performance Evaluation ◽

Eddy Covariance ◽

Sonic Anemometer ◽

Sensible Heat Flux ◽

Winter Season ◽

Populus Euphratica ◽

Tarim River ◽

Tarim River Basin ◽

Gas Analyzer ◽

Open Path

AbstractPerformance evaluation of an integrated eddy covariance (EC) instrument called the IRGASON, with a separated EC for reference, was conducted in a desert riparian Populus euphratica stand in the lower Tarim River basin in northwestern China. The separated EC consisted of an open-path gas analyzer and a sonic anemometer separated by 20 cm. The IRGASON integrates an open-path gas analyzer and a sonic anemometer into the same sensing volume, thus eliminating sensor separation in comparison to the traditional open-path EC setup. Integrating the infrared gas analyzer’s sensing head into the sensing volume of the sonic anemometer had negligible effects on wind speed and friction velocity observations of the IRGASON. Physiologically unreasonable daytime CO2 uptake was observed by both systems during the cold winter season (mean air temperature of −6.7°C), when the trees were dormant without any photosynthetic activities. The mean midday CO2 flux was −1.65 and −1.61 μmol m−2 s−1 for the IRGASON and the separated EC setup, respectively. No evidence was found for sensor self-heating as the cause of the apparent uptake CO2 flux. Instead, the uptake CO2 flux appeared to be an artifact of the spectroscopic effect of the IRGASON’s gas analyzer. After adjusting for this spectroscopic effect using a relationship with the sensible heat flux, the wintertime IRGASON CO2 flux became physiologically reasonable (mean value of −0.04 μmol m−2 s−1).

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Design of the AmeriFlux Portable Eddy Covariance System and Uncertainty Analysis of Carbon Measurements

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech2064.1 ◽

2007 ◽

Vol 24 (8) ◽

pp. 1389-1406 ◽

Cited By ~ 31

Author(s):

T. W. Ocheltree ◽

H. W. Loescher

Keyword(s):

Eddy Covariance ◽

Spatial Scales ◽

Flux Measurement ◽

Field Measurements ◽

Quality Control Laboratory ◽

Flux Measurements ◽

Eddy Covariance System ◽

Uncertainty Analyses ◽

Infrared Gas Analyzer ◽

Ambient Co2

Abstract The AmeriFlux network continues to improve the understanding of carbon, water, and energy fluxes across temporal and spatial scales. The network includes ∼120 research sites that contribute to the understanding of processes within and among ecosystems. To improve the networks ability and confidence to synthesize data across multiple sites, the AmeriFlux quality assurance and quality control laboratory was established to reduce the within- and among-site uncertainties. This paper outlines the design of the portable eddy covariance system (PECS) and subsequent data processing procedures used for site comparisons. Because the PECS makes precision measurements of atmospheric CO2, the authors also present the results of uncertainty analyses in determining the polynomials for an infrared gas analyzer, estimating the CO2 in secondary standards, and estimating ambient CO2 in field measurements. Under field conditions, drift in the measurement of CO2 increased the uncertainty in flux measurements across 7 days by 5% and was not dependent on the magnitude or direction of the flux. The maximum relative flux measurement error for unstable conditions was 10.03 μmol CO2 m−2 s−1.

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