Evapotranspiration Estimation From Infrared Surface Temperature. I: The Performance of the Flux Equation

Alves, Isabel; Fontes, J. C.; Pereira, L. S.

doi:10.13031/2013.2739

Cited by 10 publications

(5 citation statements)

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“…Hence, equality of radiometric and aerodynamic temperature, at least for composite surfaces, should not be expected. Supporting these findings, Alves et al (2000) found that radiometric surface temperature for dry conditions greatly depart from the aerodynamic temperature, which in turn will result in considerable errors in the estimation of sensible heat flux.…”

Section: Limitations and Future Challengesmentioning

confidence: 76%

ET mapping for agricultural water management: present status and challenges

et al. 2007

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Evapotranspiration (ET) is an essential component of the water balance. Remote sensing based agrometeorological models are presently most suited for estimating crop water use at both field and regional scales. Numerous ET algorithms have been developed to make use of remote sensing data acquired by sensors on airborne and satellite platforms. In this paper, a literature review was done to evaluate numerous commonly used remote sensing based algorithms for their ability to estimate regional ET accurately. The reported estimation accuracy varied from 67 to 97% for daily ET and above 94% for seasonal ET indicating that they have the potential to estimate regional ET accurately. However, there are opportunities to further improving these models for accurately estimating all energy balance components. The spatial and temporal remote sensing data from the existing set of earth observing satellite platforms are not sufficient enough to be used in the estimation of spatially distributed ET for on-farm irrigation management purposes, especially at a field scale level (*10 to 200 ha). This will be constrained further if the thermal sensors on future Landsat satellites are abandoned. However, research opportunities exist to improve the spatial and temporal resolution of ET by developing algorithms to increase the spatial resolution of reflectance and surface temperature data derived from Landsat/ ASTER/MODIS images using same/other-sensor high resolution multi-spectral images.

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Section: Limitations and Future Challengesmentioning

confidence: 76%

ET mapping for agricultural water management: present status and challenges

et al. 2007

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“…Despite some differences between temperatures for non-neutral conditions, they showed that inclusion of H using radiometric temperature improved ET estimates over those when H was neglected. Alves et al (2000a) reported radiometric temperatures up to 7°C less than aerodynamic temperatures (derived from Bowen ratio measurements in neutral conditions) for full-cover, well-watered winter wheat and iceberg lettuce in the Mediterranean climate of Portugal. They attributed their differing results to possible inaccuracies of lysimeters used in other studies, additive errors in residual methods of estimating sensible heat flux, differences in water stressed conditions, atmospheric buoyancy/stability, and especially to the greater aridity of their location in Portugal (although many of the other studies were conducted around Phoenix, Arizona).…”

Section: Introductionmentioning

confidence: 95%

“…These expressions assume that the vegetation can be reduced to a "big leaf," which is extensive, level, at height d + z oh , where all exchanges of sensible at latent heat (vapor) occur (Monteith, 1973). In the case of full cover, non-water stressed vegetation, or low atmospheric demand, the area toward the top of the canopy (between d + z oh and h c ) can also contribute significantly to vapor flux, as demonstrated by Alves et al (2000a), hence an alternative is to replace z oh with h c -d in equation (4) (Perrier, 1975). This places the big leaf at the top of the canopy.…”

Section: Energy Balance Equationsmentioning

confidence: 99%

“…A number of studies reported various levels of differences between radiometric and aerodynamic surface temperature (e.g., Huband and Monteith, 1986a;Choudhury et al, 1986;Alves et al, 2000a;2000b). The definition of aerodynamic temperature itself depends on assumptions about the heat/vapor transport roughness length (z oh ), which cannot be measured directly, and is therefore usually assumed to be 0.1 to 0.2 of momentum roughness length (z om ), since sensible heat transfer by diffusion is governed by momentum exchange.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of aerodynamic and radiometric surface temperature using precision weighing lysimeters

et al. 2004

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Radiometric surface temperature (T s ) is commonly used as a surrogate for aerodynamic temperature (T o ) in computing the sensible heat flux term (H) in the energy balance. However, these temperatures may differ by several degrees, leading to possible errors (especially for large H) and their relationship is not well known. Previous researchers have established empirical and semi-empirical parameterizations of the radiometric roughness length (z or ) or some related form (e.g., kB r -1 = ln[z om /z or ], where z om is the momentum roughness length). In this paper, we estimated T o -T a (where T a is air temperature at 2 m height) and z or using large, precision weighing lysimeters planted with irrigated alfalfa, irrigated and dryland cotton, and dryland grain sorghum. T s was measured by infrared thermometers mounted over the lysimeters. No apparent relations were found between (T o -T a ) and (T s -T a ) or between z or (in the kB r -1 form) and meteorological variables or leaf area index (LAI). The kB r -1 parameter appeared to be most influenced by the different surface roughness of each crop type. Using constant kB r -1 values established for each type of surface, the energy balance model showed reasonable agreement with H and LE derived from lysimeter measurements.

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“…This difference leads to errors in the estimation of H, which in turn leads to errors in the estimation of LE and ET through equation 1. Along those lines, Choudbury et al (1986), Kustas and Norman (1996), Chehbouni et al (1997a), Alves et al (2000), Nagar et al (2002), Crago et al (2004), and Yaoming et al (2003) reported similar findings. They showed differences between T o and T s ranging from less than 2°C to 3°C for uniform canopy covers to 10°C to 15°C for partial surface vegetation cover.…”

mentioning

confidence: 71%

Surface Aerodynamic Temperature Modeling over Rainfed Cotton

Chávez¹,

Howell²,

Gowda³

et al. 2010

Transactions of the ASABE

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Evapotranspiration (ET) or latent heat flux (LE) can be spatially estimated as an energy balance (EB) residual for land surfaces using remote sensing inputs. The EB equation requires the estimation of net radiation (R n), soil heat flux (G), and sensible heat flux (H). R n and G can be estimated with an acceptable accuracy. In computing H, radiometric surface temperature (T s) is often used instead of surface aerodynamic temperature (T o), as T o is neither measured nor easily estimated. This may cause an underestimation of ET because H will be overestimated as T s is typically larger than T o for unstable atmospheric conditions. The objectives of this study were to (1) model T o to improve the estimation of H and consequently ET for advective environments in the semi-arid Texas High Plains, and (2) assess the accuracy of the T o model using three different methods (aerodynamic profile, lysimeter, and eddy covariance). A 6.5 m tower platform was used to measure profiles of wind speed, air temperature, and relative humidity in and above cotton canopy near a large weighing lysimeter managed under rainfed conditions at the

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Evapotranspiration Estimation From Infrared Surface Temperature. I: The Performance of the Flux Equation

Cited by 10 publications

References 0 publications

ET mapping for agricultural water management: present status and challenges

ET mapping for agricultural water management: present status and challenges

Comparison of aerodynamic and radiometric surface temperature using precision weighing lysimeters

Surface Aerodynamic Temperature Modeling over Rainfed Cotton

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