scholarly journals Application of the Flux-Variance Technique for Evapotranspiration Estimates in Three Types of Agricultural Structures

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Ori Ahiman ◽  
Yonatan Mekhmandarov ◽  
Moran Pirkner ◽  
Josef Tanny
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Turbulent Transport ◽  
Control Analysis ◽  
Energy Balance Closure ◽  
Tomato Crop ◽  
Simple Method

Irrigation of protected crops requires sound knowledge of evapotranspiration. Previous studies have established that the eddy-covariance (EC) technique is suitable for whole canopy evapotranspiration measurements in large agricultural screenhouses. Nevertheless, the eddy-covariance technique remains difficult to apply in the farm due to costs, operational complexity, and postprocessing of data, thereby inviting alternative techniques to be developed. The subject of this paper is the evaluation of a turbulent transport technique, the flux variance (FV), whose instrumentation needs and operational demands are not as elaborate as the EC, to estimate evapotranspiration within large agricultural structures. Measurements were carried out in three types of agricultural structures: (i) a banana plantation in a light-shading (8%) screenhouse (S1), (ii) a pepper crop in an insect-proof (50-mesh) screenhouse (S2), and (iii) a tomato crop in a naturally ventilated greenhouse with a plastic roof and 50-mesh screened sidewalls (S3). Quality control analysis of the EC data showed that turbulence development and flow stationarity conditions in the three structures were suitable for flux measurements. However, within the insect-proof screenhouse (below the screen) and the plastic-covered greenhouse, R2 of the energy balance closure was poor; hence, the alternative simple method could not be used. Results showed that the FV technique was suitable for reliable estimates of ET in shading and insect-proof screenhouses with R2 of the regressions between FV latent heat flux and latent heat flux deduced from energy balance closure of 0.99 and 0.92 during validation for S1 and S2, respectively.

Comparison of energy fluxes from eddy covariance and scintillometer over an agricultural field

2020 ◽  
Author(s):  
Matěj Orság ◽  
Milan Fischer ◽  
Josef Eitzinger ◽  
Miroslav Trnka
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Soil Heat Flux ◽  
Radiation Balance ◽  
Energy Balance Closure ◽  
Sensible Heat ◽  
Agricultural Field ◽  
Available Energy

<p>In this study we compare turbulent energy fluxes obtained from eddy covariance (EC) (LI-7500A, LI-COR + Windmaster, Gill Instruments) and large aperture scintillometer (BLS900, Scintec) over an agricultural field (wheat field, straw and bare soil). As the EC method provides direct measurements of sensible heat (H<sub>EC</sub>) and latent heat (LE<sub>EC</sub>) fluxes we use it as a reference method. The EC method enables to determine fluxes within a footprint centered around the point of measurement in the middle of the field. The scintillometer provides an estimation of sensible heat flux (H<sub>SC</sub>), derived from air refractive index fluctuation integrated over the measurement path length, in this case 570 m diagonally across whole field. The reference measurements of the radiation balance components consist of 4-component net radiometer for net radiation (Rn) (NR01, Hukseflux), three soil heat flux plates for soil heat flux (G) monitoring (HFP01, Hukseflux), including thermocouples for quantification of the heat storage above the soil heat flux plates. The scintillometer-based latent heat (LE<sub>SC</sub>) is calculated as a residuum from available energy (Rn-G) and H<sub>SC</sub>, provided by scintillometer. The measurement of radiation balance components was located at the top of 3.5 m mast with the EC system, while the soil heat flux plates were collocated around in 5 cm depth. The site is a flat, rectangular agricultural field (app. 16.5 ha), in the north-eastern Austria, Danube river lowland (48.21N, 16.622E), sown with winter wheat during growing season 2019. The measurement campaign was established in February 2019 with aim for multi-seasonal monitoring. The EC measurement height is 2.7 m, the scintillometer transmitter and receiver are fixed on 4 m masts, facing towards each other from NW and SE corners of the field.</p><p>Comparison of the EC-based turbulent fluxes (H<sub>EC</sub>+LE<sub>EC</sub>) and the available energy (Rn-G) during the period March to Mid-June showed a very good agreement, resulting in the energy balance closure of 0.96 (R<sup>2 </sup>= 0.93). This suggest high accuracy and robustness of the measurement setup together with the ability of the EC method to capture all scales of eddies responsible for energy transport at this site. The comparison of methods indicates that H<sub>SC</sub> overestimated H<sub>EC</sub> by 10 % (R<sup>2 </sup>= 0.74) and LE<sub>SC</sub> underestimated LE<sub>EC</sub> by 13 % (R<sup>2 </sup>= 0.81). Related to Rn, the H<sub>EC</sub>, LE<sub>EC</sub> and G fluxes accounted for 22 % (R<sup>2 </sup>= 0.53), 59 % (R<sup>2 </sup>= 0.70) and 15% (R<sup>2 </sup>= 0.62) of the Rn flux, respectively. We assume that the combination of EC and scintillometer method has a potential to bring deeper insight into the analysis of the energy balance closure problem.</p>

scholarly journals Comparing Aircraft-Based Remotely Sensed Energy Balance Fluxes with Eddy Covariance Tower Data Using Heat Flux Source Area Functions

2005 ◽  
Vol 6 (6) ◽  
pp. 923-940 ◽  
Author(s):  
JoséL. Chávez ◽  
Christopher M. U. Neale ◽  
Lawrence E. Hipps ◽  
John H. Prueger ◽  
William P. Kustas
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sensible Heat Flux ◽  
Source Area ◽  
Soil Heat Flux ◽  
Sensible Heat ◽  
Atmospheric Conditions

Abstract In an effort to better evaluate distributed airborne remotely sensed sensible and latent heat flux estimates, two heat flux source area (footprint) models were applied to the imagery, and their pixel weighting/integrating functionality was investigated through statistical analysis. Soil heat flux and sensible heat flux models were calibrated. The latent heat flux was determined as a residual from the energy balance equation. The resulting raster images were integrated using the 2D footprints and were compared to eddy covariance energy balance flux measurements. The results show latent heat flux estimates (adjusted for closure) with errors of (mean ± std dev) −9.2 ± 39.4 W m−2, sensible heat flux estimate errors of 9.4 ± 28.3 W m−2, net radiation error of −4.8 ± 20.7 W m−2, and soil heat flux error of −0.5 ± 24.5 W m−2. This good agreement with measured values indicates that the adopted methodology for estimating the energy balance components, using high-resolution airborne multispectral imagery, is appropriate for modeling latent heat fluxes. The method worked well for the unstable atmospheric conditions of the study. The footprint weighting/integration models tested indicate that they perform better than simple pixel averages upwind from the flux stations. In particular the flux source area model (footprint) seemed to better integrate the resulting heat flux image pixels. It is suggested that future studies test the methodology for heterogeneous surfaces under stable atmospheric conditions.

scholarly journals On the Use of the Eddy Covariance Latent Heat Flux and Sap Flow Transpiration for the Validation of a Surface Energy Balance Model

2018 ◽  
Vol 10 (2) ◽  
pp. 195 ◽  
Author(s):  
Antonino Maltese ◽  
Hassan Awada ◽  
Fulvio Capodici ◽  
Giuseppe Ciraolo ◽  
Goffredo La Loggia ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sap Flow ◽  
Surface Energy Balance ◽  
Energy Balance Model ◽  
Balance Model

scholarly journals Micrometeorological methods to estimate sugarcane evapotranspiration in coastal northeastern region of Brazil

2019 ◽  
pp. 1422-1428
Author(s):  
Adolpho Emanuel Quintela da Rocha ◽  
José Leonaldo de Souza ◽  
Guilherme Bastos Lyra ◽  
Ricardo Araújo Ferreira Junior ◽  
Gustavo Bastos Lyra ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Bowen Ratio ◽  
Water Vapour Pressure ◽  
Sensible Heat ◽  
Energy Balance Method ◽  
Ratio Energy

The aim of the present work was to evaluate the performance of Bowen ratio-energy balance method, as well as the energy balance closure by Eddy covariance technique for a sugarcane crop in Brazilian northeastern region. Micrometeorological measurements were carried out between June 7th and November 17th, 2013. Latent and sensible heat fluxes were determined through Eddy covariance technique (EC) and by the Bowen ratio-energy balance method (BREB), considering two approaches. The first, estimated the air temperature and water vapour pressure gradient in two levels above the canopy. The second method measured the air temperature and water vapour pressure at the first level and the surface temperature from radiometric measurements. Latent heat flux was also estimated as energy balance residue from determinations of the sensible heat flux by Eddy covariance. The degree of energy balance closure was dependent on the time of the day considered. Bowen ratio - energy balance estimated from the first approach, showed the best agreement with the eddy covariance measurements to estimate latent heat flux, while in the second case, when the Bowen ratio was estimated using the surface temperature, the linear relationship was the most discrepant. Therefore, the Bowen ratio conventional method is more suitable for estimating latent heat flux in sugarcane.

scholarly journals Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

2017 ◽  
Vol 21 (7) ◽  
pp. 3401-3415 ◽  
Author(s):  
Nobuhle P. Majozi ◽  
Chris M. Mannaerts ◽  
Abel Ramoelo ◽  
Renaud Mathieu ◽  
Alecia Nickless ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Latent Heat ◽  
Surface Energy Balance ◽  
Sensible Heat Flux ◽  
Dry Season ◽  
Energy Balance Closure ◽  
Net Radiation ◽  
Wet Season

Abstract. Flux towers provide essential terrestrial climate, water, and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based Earth observation and monitoring efforts, such as assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches. In this paper, 15 years of Skukuza eddy covariance data, i.e. from 2000 to 2014, were analysed for surface energy balance closure (EBC) and partitioning. The surface energy balance closure was evaluated using the ordinary least squares regression (OLS) of turbulent energy fluxes (sensible (H) and latent heat (LE)) against available energy (net radiation (Rn) less soil heat (G)), and the energy balance ratio (EBR). Partitioning of the surface energy during the wet and dry seasons was also investigated, as well as how it is affected by atmospheric vapour pressure deficit (VPD), and net radiation. After filtering years with low-quality data (2004–2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed the wet season with 1.17 and spring (1.02) being closest to unity, with the dry season (0.70) having the highest imbalance. Nocturnal surface energy closure was very low at 0.26, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity. The energy partition analysis showed that sensible heat flux is the dominant portion of net radiation, especially between March and October, followed by latent heat flux, and lastly the soil heat flux, and during the wet season where latent heat flux dominated sensible heat flux. An increase in net radiation was characterized by an increase in both LE and H, with LE showing a higher rate of increase than H in the wet season, and the reverse happening during the dry season. An increase in VPD is correlated with a decrease in LE and increase in H during the wet season, and an increase in both fluxes during the dry season.

scholarly journals Energy balance measurements over a banana orchard in the Semiarid region in the Northeast of Brazil

2009 ◽  
Vol 44 (11) ◽  
pp. 1365-1373 ◽  
Author(s):  
Carlos Antonio Costa dos Santos ◽  
Bernardo Barbosa da Silva ◽  
Tantravahi Venkata Ramana Rao ◽  
Christopher Michael Usher Neale
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Eddy Covariance ◽  
Heat Fluxes ◽  
Irrigation District ◽  
Semiarid Region ◽  
Energy Balance Closure ◽  
Wet Season ◽  
Growing Seasons ◽  
Eddy Covariance System

The objective of this work was to evaluate the reliability of eddy covariance measurements, analyzing the energy balance components, evapotranspiration and energy balance closure in dry and wet growing seasons, in a banana orchard. The experiment was carried out at a farm located within the irrigation district of Quixeré, in the Lower Jaguaribe basin, in Ceará state, Brazil. An eddy covariance system was used to measure the turbulent flux. An automatic weather station was installed in a grass field to obtain the reference evapotranspiration (ET0) from the combined FAO-Penman-Monteith method. Wind speed and vapor pressure deficit are the most important variables on the evaporative process in both growing seasons. In the dry season, the heat fluxes have a similar order of magnitude, and during the wet season the latent heat flux is the largest. The eddy covariance system had acceptable reliability in measuring heat flux, with actual evapotranspiration results comparing well with those obtained by using the water balance method. The energy balance closure had good results for the study area, with mean values of 0.93 and 0.86 for the dry and wet growing seasons respectively.

scholarly journals Diurnal Energy Balance in a Mango Orchard in the Northeast of Pará, Brazil

2018 ◽  
Vol 33 (3) ◽  
pp. 537-546 ◽  
Author(s):  
Paulo Jorge de Oliveira Ponte de Souza ◽  
Juliana Chagas Rodrigues ◽  
Adriano Marlisom Leão de Sousa ◽  
Everaldo Barreiros de Souza
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Soil Cover ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Net Radiation ◽  
Growing Seasons ◽  
Available Energy

Abstract This study aimed to evaluate the diurnal energy balance during the reproductive stage of two growing seasons of a mango orchard in the northeast of Pará, Brazil. Therefore, a micrometeorological tower was installed and instrumented, in the center of the experimental area, to monitor meteorological variables, besides the phenological evaluation of the mango orchard, which was carried out during growing seasons of 2010-2011 (October 2010 to January 2011) and of 2011-2012 (September 2011 to January 2012). The energy balance was obtained by the bowen ration technique, and the available energy partitioned into heat flux to the ground, sensible heat and latent heat. The amount of rainfall was crucial to the partition of the net radiation in the energy balance components. It provided the variation in the consumption of available energy between 69% and 78% as latent heat flux, and between 23% and 32% as sensible heat flux. The heat flux to the ground was small, representing less than 1% of the net radiation, showing that the mango orchard exhibits good soil cover preventing large variations in soil heating.

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