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Wheat is one of the crops occupying the largest areas in the world (218 million ha in 2013). Understanding the land-atmosphere energy exchanges over these croplands becomes important not only for agronomy but also for climatic and meteorological aspects. This study continues previous work on the estimation of actual evapotranspiration (ET) and the assessment of crop coefficients of sorghum, sunflower, or canola. Two variations of a simple two-source energy balance (STSEB) approach were used in combination with land surface temperature measurements to calculate hourly and daily values of surface fluxes and actual ET. An experiment was carried out during the spring season of 2014 in Las Tiesas experimental farm in Barrax, Spain. Soil and canopy temperature components together with meteorological variables and biophysical parameters were measured from planting to senescence. Comparison to lysimeter measurements showed calculation errors of ±0.11 mm h and ±0.8 mm day for hourly and daily ET values, respectively, whereas an underestimation no >4 % resulted from the entire campaign. Partition between soil and canopy components yielded a ratio of evaporation ( E) to transpiration ( T) of 36-64 %, respectively, for the total growing season. Dual crop coefficients were also calculated and compared to those proposed by FAO-56. Although separate E and T measurements were not available, similar results between the STSEB and FAO-56 models demonstrate the utility of the STSEB for investigating management strategies aimed at increasing crop water use efficiency. [ABSTRACT FROM AUTHOR]

Estimates of surface actual evapotranspiration (ET) can assist in predicting crop water requirements. An alternative to the traditional crop-coefficient methods are the energy balance models. The objective of this research was to show how surface temperature observations can be used, together with a two-source energy balance model, to determine crop water use throughout the different phenological stages of a crop grown. Radiometric temperatures were collected in a sorghum (Sorghum bicolor) field as part of an experimental campaign carried out in Barrax, Spain, during the 2010 summer growing season. Performance of the Simplified Two-Source Energy Balance (STSEB) model was evaluated by comparison of estimated ET with values measured on a weighing lysimeter. Errors of ±0.14mmh-1 and ±1.0mmd-1 were obtained at hourly and daily scales, respectively. Total accumulated crop water use during the campaign was underestimated by 5 %. It is then shown that thermal radiometry can provide precise crop water necessities and is a promising tool for irrigation management. [ABSTRACT FROM AUTHOR]

Boreal forests occupy about 11% of the terrestrial surface and represent an important contribution to global energy balance. The ground measurement of daily evapotranspiration (LEd) is very difficult due to the limitations on experiments. The objective of this paper is to present and explore the applicability of the B-method for monitoring actual LEd in these ecosystems. The method shown in this paper allows us to determine the surface fluxes over boreal forests on a daily basis from instantaneous information registered in a conventional meteorological tower, as well as the canopy temperature (T c) retrieved by satellite. Images collected by the MODIS (moderate resolution imaging spectroradiometer) on board EOS-Terra have been used for this study. The parameters of the model were calibrated from the SIFLEX-2002 (Solar Induced Fluorescence Experiment 2002) campaign dataset in a northern boreal forest in Finland. A study of these parameters was made on an hourly basis in order to make the method applicable, not only at midday but within an interval of 7 h around it. This is an important advance with respect to the original formulation of this approach since the overpass time of satellites can be very variable. The comparison between T c ground measured with a thermal infrared radiometer, and T c retrieved from land surface temperature (LST) MODIS data, showed an estimation error of ±1.4°C for viewing angles from 5 to 60°. A complete sensitivity analysis was carried out and an estimation error of about ±35%, corresponding to the interval 10.00-11.00 h UTC, was shown as the lowest in LEd retrieval. Finally, the method was validated over the study site using 21 MODIS images for 2002 and 2003. The results were compared with eddy-correlation ground measurements. An accuracy of ±1.0 mm/day and an overestimation of 0.3 mm/day were shown in the LEd retrieval. [ABSTRACT FROM AUTHOR]

Summary: The increasing interest of hydrological, climatic and meteorological models in the different components of the surface energy balance has encouraged the development of operational methods for estimating surface energy fluxes at a regional scale. In this paper, a sequence of three high-resolution satellite-based surface energy fluxes images are analyzed over an extensive area with a large variety of land uses. Two images from Landsat 7-ETM+ (1999, 2002) and one from Landsat 5-TM (2004) are collected covering the whole Basilicata region (Southern Italy). A Simplified version of a Two-Source Energy Balance (STSEB) model is used to retrieve the surface sensible heat flux. A balance between the long-wave and short-wave radiation is applied to extract the net radiation flux. The evapotranspiration (LE) is obtained as a residual term of the energy balance equation. The different croplands are characterized from the CORINE Land Cover maps, and the required meteorological variables are obtained by interpolating the data of a network of agro-meteorological stations distributed within the region. Atmospheric profiles from radiosoundings are used in the radiative transfer model MODTRAN 4.0 to correct the satellite data. Maps of the different fluxes are produced. Daily LE results are compared with some ground measurements, and an analysis is made taking the land use classification as a basis. An accuracy close to 1mmday−1 is obtained. This value is in agreement with the typical uncertainties reported in the literature. [Copyright &y& Elsevier]

Accurate evapotranspiration (ET) estimations based on surface energy balance from remote sensing require information in the thermal infrared (TIR) domain, normally provided with an insufficient spatial resolution. In order to estimate ET in heterogeneous agricultural areas, we inspect in this paper the use of disaggregation techniques applied to two different sensors, such as MODIS (daily revisit cycle and 1 km spatial resolution in the TIR domain) and Spot 5 (5 days revisit cycle and 10 m spatial resolution in the VNIR bands but no TIR band). Spot 5 images were used as a proxy for upcoming Sentinel-2. The Simplified Two-Source Energy Balance (STSEB) model was used for the estimation of ET. Since no Sentinel-2 images were available yet, images from the Spot 5 Take 5 experiment were used for testing this approach. Results assessment was conducted at two different levels: field scale (using ground data), and scene scale (using Landsat 7-ETM + images as a reference). Validation of both disaggregated land surface temperature (LST) and derived surface energy fluxes was performed. Mean absolute deviations of ~ 2 °C in disaggregated LST were observed at both field and scene scales. At field scale, relative errors of 22% and 19% were obtained for ET at instantaneous and daily scales, respectively. At scene scale, the four components of the surface energy balance equation were obtained with relative errors of 3, 14, 11 and 8% for net radiation, evapotranspiration, sensible heat flux and soil heat flux, respectively, compared to Landsat. The results obtained were compared to the use of the MODIS LST at its original resolution (1 km), which was used also to obtain the surface energy fluxes. As the surface heterogeneity increases the errors in both MODIS LST and ET become more and more significant, compared to the use of the disaggregated images. Although reference images at 10 m spatial resolution were not available at this stage for a more robust comparison, this paper shows the potential of the use of disaggregated LST to estimate ET at 10 m spatial resolution, which is especially attractive in highly heterogeneous areas. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new technique to perform local adjustments in the crop coefficients is presented. [•] Local measurements of radiometric temperatures are the basis of this technique. [•] Surface energy balance of sunflower and canola was performed. [•] Evapotranspiration results were compared to lysimeter measurements. [•] Evaporation/Transpiration results were used to assess crop coefficients. [ABSTRACT FROM AUTHOR]