scholarly journals Avaliação de modelos de footprint para análise de fluxos obtidos por Eddy-Covariance em pequenas-áreas

2018 ◽  
Vol 40 ◽  
pp. 93
Author(s):  
Ivan Mauricio Cely Toro ◽  
Ricardo Acosta Gotuzzo ◽  
Débora Regina Roberti ◽  
Jackson Ernani Fiorin
Keyword(s):  
Boundary Layer ◽  
Eddy Covariance ◽  
Analytical Models ◽  
Agricultural Field ◽  
Footprint Model ◽  
Scalar Fluxes ◽  
Equation Boundary ◽  
Small Fields ◽  
Flux Measurements ◽  
Eddy Covariance System

Two models for footprint calculations are compared employing flux measurements in the planetary boundary layer. The calculationsare based on the analytical models by Kormann e Meixner (2001) [An analytical footprint model for non-neutral stratification.Boundary-Layer Meteorology 99, 207–224] and by Schuepp et al. (1990) [Footprint prediction of scalar fluxes from analytical solutions of the difussion equation. Boundary-Layer Meteorology 50, 355-373]. The footprint density functions of a flux sensor are determined using eddy-covariance data. Those functions are integrated over surfaces given by quadrangular rectangles, in this case an agricultural field. This work ilustrates the features of each footprint model employing flux measurements with an eddy-covariance system of the SULFLUX network, installed on a agricultural field. Finally, it is presented the model that describes in a better way the flux measurements in small fields.

Surface energy flux measurements in a flooded and an aerobic rice field using a single eddy-covariance system

2014 ◽  
Vol 13 (4) ◽  
pp. 405-424 ◽  
Author(s):  
Daniele Masseroni ◽  
Arianna Facchi ◽  
Marco Romani ◽  
Enrico Antonio Chiaradia ◽  
Olfa Gharsallah ◽  
...  
Keyword(s):  
Surface Energy ◽  
Eddy Covariance ◽  
Energy Flux ◽  
Rice Field ◽  
Aerobic Rice ◽  
Surface Energy Flux ◽  
Flux Measurements ◽  
Eddy Covariance System

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

2007 ◽  
Vol 24 (8) ◽  
pp. 1389-1406 ◽  
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.

First application of low-cost eddy covariance for CO2 fluxes over agroforestry

2020 ◽  
Author(s):  
Justus van Ramshorst ◽  
Christian Markwitz ◽  
Timothy Hill ◽  
Robert Clement ◽  
Alexander Knohl ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Low Cost ◽  
Net Ecosystem Exchange ◽  
Agroforestry Systems ◽  
Agricultural System ◽  
Data Series ◽  
Custom Made ◽  
Flux Measurements ◽  
Eddy Covariance System ◽  
The Difference

<p>Agroforestry is a combination of monoculture agriculture and trees. Studies of net ecosystem exchange of CO<sub>2</sub> (NEE) of agroforestry systems are rare, in comparison to the extensive studies of NEE of agricultural systems (croplands and grasslands). Agroforestry has been shown to alter the microclimate, productivity, and nutrient and water usage – as compared to standard agricultural practise. The, potentially, higher carbon sequestration of agroforestry, relative to monoculture systems, provides an interesting option for mitigating climate change, highlighting the need for improved study of agroforestry systems. The current study, as part of the SIGNAL (sustainable intensification of agriculture through agroforestry) project, investigates NEE of agroforestry compared to that of monoculture agriculture. The study employs paired comparisons of flux measurements above agroforestry and monoculture agronomy, replicated at five locations across Germany. Fluxes are measured, using innovative low-cost CO<sub>2</sub> eddy covariance sensors (slow response Vaisala GMP343 IRGA with custom made housing), which have been successfully used in a study over grassland. Continuous data series from mid-summer until winter 2019 show that both systems acted as a sink with comparable fluxes during summer. The diurnal CO<sub>2</sub> cycle and the response to management activities are distinguishable and in autumn preliminary results suggest a small difference in fluxes between the two systems. The low-cost eddy covariance system is able to capture the turbulence and to measure the CO<sub>2</sub> flux over the agroforestry and monoculture agricultural system. We aim to further improve the quality of the CO<sub>2</sub> fluxes, by adapting post-processing software to better estimate the difference in carbon uptake between the agroforestry and monoculture systems.</p>

scholarly journals Eddy covariance methane flux measurements over a grazed pasture: effect of cows as moving point sources

2015 ◽  
Vol 12 (12) ◽  
pp. 3925-3940 ◽  
Author(s):  
R. Felber ◽  
A. Münger ◽  
A. Neftel ◽  
C. Ammann
Keyword(s):  
Eddy Covariance ◽  
Methane Flux ◽  
Point Sources ◽  
Carbon Dioxide Exchange ◽  
Systematic Effect ◽  
Footprint Model ◽  
Grazed Pasture ◽  
Grazing System ◽  
Methane Fluxes ◽  
Flux Measurements

Abstract. Methane (CH4) from ruminants contributes one-third of global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH4 analyzers, the instrumentation at many flux sites has been amended for these gases. However, the application of EC over pastures is challenging due to the spatially and temporally uneven distribution of CH4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d−1) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to 2 orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH4 head−1 d−1 (best estimate from this study) correspond well to animal respiration chamber measurements reported in the literature. However, a systematic effect of the distance between source and EC tower on cow emissions was found, which is attributed to the analytical footprint model used. We show that the EC method allows one to determine CH4 emissions of cows on a pasture if the data evaluation is adjusted for this purpose and if some cow distribution information is available.

scholarly journals Eddy covariance methane flux measurements over a grazed pasture: effect of cows as moving point sources

2015 ◽  
Vol 12 (4) ◽  
pp. 3419-3468 ◽  
Author(s):  
R. Felber ◽  
A. Münger ◽  
A. Neftel ◽  
C. Ammann
Keyword(s):  
Eddy Covariance ◽  
Methane Flux ◽  
Point Sources ◽  
Carbon Dioxide Exchange ◽  
Systematic Effect ◽  
Footprint Model ◽  
Grazed Pasture ◽  
Grazing System ◽  
Methane Fluxes ◽  
Flux Measurements

Abstract. Methane (CH4) from ruminants contributes one third to global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH4 analysers the instrumentation at many flux sites have been amended for these gases. However the application of EC over pastures is challenging due to the spatial and temporal uneven distribution of CH4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d−1) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to two orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH4 head−1 d−1 (best guess of this study) correspond well to animal respiration chamber measurements reported in the literature. However a systematic effect of the distance between source and EC tower on cow emissions was found which is attributed to the analytical footprint model used. We show that the EC method allows to determine CH4 emissions of grazing cows if the data evaluation is adjusted for this purpose and if some cow distribution information is available.

scholarly journals Comparative measurements of water vapor fluxes over a tall forest using open- and closed-path eddy covariance system

2015 ◽  
Vol 8 (5) ◽  
pp. 4711-4736
Author(s):  
J. B. Wu ◽  
X. Y. Zhou ◽  
A. Z. Wang ◽  
F. H. Yuan
Keyword(s):  
Water Vapor ◽  
Eddy Covariance ◽  
Time Lag ◽  
Sonic Anemometer ◽  
Co2 Flux ◽  
Closed Path ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Flux Measurements ◽  
Eddy Covariance System

Abstract. Eddy covariance using infrared gas analyses has been a useful tool for gas exchange measurements between soil, vegetation and atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO2 flux estimations, while lacking in the comparison of water vapor flux estimations. In this study, the specific performance of water vapor flux measurements of an open-path eddy covariance (OP) system was compared against a CP system over a tall temperate forest in Northeast China. The results show that the fluxes from the OP system (LEop) were generally greater than the (LEcp though the two systems shared one sonic anemometer. The tube delay of closed-path analyser depended on relative humidity, and the fixed median time lag contributed to a significant underestimation of (LEcp between the forest and atmosphere, while slight systematic overestimation was also found for covariance maximization method with single broad time lag search window. After the optimized time lag compensation was made, the average difference between the 30 min (LEop and (LEcp was generally within 6%. Integrated over the annual cycle, the CP system yielded a 5.1% underestimation of forest evapotranspiration as compared to the OP system measurements (493 vs. 469 mm yr−1). This study indicates the importance to estimate the sampling tube delay accurately for water vapor flux calculations with closed-path analysers, and it also suggests that when discuss the energy balance closure problem in flux sites with closed-path eddy covariance systems, it has to be aware that some of the imbalance is possibly caused by the systematic underestimation of water vapor fluxes.

scholarly journals An Approximate Footprint Model for Flux Measurements in the Convective Boundary Layer

2006 ◽  
Vol 23 (10) ◽  
pp. 1384-1394 ◽  
Author(s):  
Weiguo Wang ◽  
Kenneth J. Davis ◽  
Daniel M. Ricciuto ◽  
Martha P. Butler
Keyword(s):  
Boundary Layer ◽  
Stochastic Model ◽  
Convective Boundary Layer ◽  
Vertical Direction ◽  
Atmospheric Conditions ◽  
Flux Footprint ◽  
Convective Boundary ◽  
Obukhov Length ◽  
Footprint Model ◽  
Flux Measurements

Abstract An explicit footprint model for flux measurements of passive scalars in the lower part of the convective boundary layer (CBL) is introduced. A simple footprint model is derived analytically in an idealized CBL. The simple model can simulate the overall characteristics of the flux footprint. Then a method is proposed to adjust the analytical solutions to those from a Lagrangian stochastic model that considers more realistic atmospheric conditions in the vertical direction. The adjusted footprint model is a function of Monin–Obukhov length (L), roughness length, receptor height, and CBL depth (h). Comparison between the results from the adjusted footprint model and stochastic model suggests that the adjusted footprint model can well simulate the streamwise extent of the footprint within the dimensionless upwind distance X < 1, which accounts for a majority of the footprint. The model applies to stabilities of –L/h between 0.01 and 0.1 and roughness lengths between 10−5 and 2 × 10−3h in the lower part of the mixed layer (from 0.1h to 0.6h).

scholarly journals Eddy covariance flux measurements confirm extreme CH<sub>4</sub> emissions from a Swiss hydropower reservoir and resolve their short-term variability

2011 ◽  
Vol 8 (9) ◽  
pp. 2815-2831 ◽  
Author(s):  
W. Eugster ◽  
T. DelSontro ◽  
S. Sobek
Keyword(s):  
Greenhouse Gas ◽  
Eddy Covariance ◽  
Land Surface ◽  
Lake Level ◽  
Driving Forces ◽  
Open Water ◽  
Short Term ◽  
Flux Measurements ◽  
Floating Chamber ◽  
Hydropower Reservoir

Abstract. Greenhouse gas budgets quantified via land-surface eddy covariance (EC) flux sites differ significantly from those obtained via inverse modeling. A possible reason for the discrepancy between methods may be our gap in quantitative knowledge of methane (CH4) fluxes. In this study we carried out EC flux measurements during two intensive campaigns in summer 2008 to quantify methane flux from a hydropower reservoir and link its temporal variability to environmental driving forces: water temperature and pressure changes (atmospheric and due to changes in lake level). Methane fluxes were extremely high and highly variable, but consistently showed gas efflux from the lake when the wind was approaching the EC sensors across the open water, as confirmed by floating chamber flux measurements. The average flux was 3.8 ± 0.4 μg C m−2 s−1 (mean ± SE) with a median of 1.4 μg C m−2 s−1, which is quite high even compared to tropical reservoirs. Floating chamber fluxes from four selected days confirmed such high fluxes with 7.4 ± 1.3 μg C m−2 s−1. Fluxes increased exponentially with increasing temperatures, but were decreasing exponentially with increasing atmospheric and/or lake level pressure. A multiple regression using lake surface temperatures (0.1 m depth), temperature at depth (10 m deep in front of the dam), atmospheric pressure, and lake level was able to explain 35.4% of the overall variance. This best fit included each variable averaged over a 9-h moving window, plus the respective short-term residuals thereof. We estimate that an annual average of 3% of the particulate organic matter (POM) input via the river is sufficient to sustain these large CH4 fluxes. To compensate the global warming potential associated with the CH4 effluxes from this hydropower reservoir a 1.3 to 3.7 times larger terrestrial area with net carbon dioxide uptake is needed if a European-scale compilation of grasslands, croplands and forests is taken as reference. This indicates the potential relevance of temperate reservoirs and lakes in local and regional greenhouse gas budgets.

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