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M J Savage - One of the best experts on this subject based on the ideXlab platform.
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surface renewal method for estimating Sensible Heat Flux
Water SA, 2010Co-Authors: M G Mengistu, M J SavageAbstract:For short canopies, latent energy Flux may be estimated using a shortened surface energy balance from measurements of Sensible and soil Heat Flux and the net irradiance at the surface. The surface renewal (SR) method for estimating Sensible Heat, latent energy, and other scalar Fluxes has the advantage over other micrometeorological methods since the method requires only measurement of the scalar of interest at a point and the method may be applied close to the canopy surface, thereby reducing fetch requirements. The SR analysis for estimating Sensible Heat Flux from canopies involves highfrequency air-temperature measurements (typically 2 to 10 Hz) using unshielded and naturally-ventilated 25- to 75-mm diameter fine-wire thermocouples. The SR method is based on the premise that a parcel of air connected to the surface, after it has been enriched or depleted, is renewed by an air parcel from above. There are 2 SR analysis approaches: the ideal SR analysis approach which presumes a constant α factor; and a set of SR approaches that avoid the use of the α calibration factor. The weighting factor α depends on measurement height, canopy structure and stability conditions since it depends on the capability of the highest frequency eddies to mix the scalar within the air parcels renewed by coherent structures. A combination approach using SR and either similarity theory, that requires friction velocity or wind-speed measurements, or dissipation theory, has also been used to estimate H. The combination SR and dissipation method only requires high-frequency air-temperature data and may be considered not to require calibration. The ideal SR and combination SR/ dissipation approaches are the least expensive micrometeorological methods for estimating Sensible Heat Flux and also latent energy Flux if one forces closure of the surface energy balance. However, application of SR analysis using slow data-loggers require some expertise since high-frequency air temperature data are not usually stored with the slower data-loggers. Some structure functions can be stored for post-processing and determination of ramp amplitude and ramp period, but the appropriate time lags have to be chosen a priori. Fortunately, modern data-loggers avoid this problem and complex SR analysis approaches can now be applied. However, for routine purposes, applications using the ideal SR analysis approach with slow data-loggers may be of interest since it is a very affordable method. Keywords: surface energy balance, Sensible Heat Flux, latent energy Flux, evaporation
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Sensible Heat Flux by surface layer scintillometry and eddy covariance over a mixed grassland community as affected by bowen ratio and most formulations for unstable conditions
Journal of Hydrometeorology, 2009Co-Authors: George O. Odhiambo, M J SavageAbstract:Abstract Measurements of Sensible Heat Flux for an extended period for unstable conditions using surface layer scintillometry (SLS) and eddy covariance (EC) and supplemented by Bowen ratio measurements for a mixed grassland community on the eastern seaboard of South Africa are presented. Measurements of SLS Sensible Heat Flux density were compared with those obtained using EC for a wide range of Bowen ratio (β). Also presented is an analysis of the different forms of the Monin–Obukhov similarity theory (MOST) functions used in micrometeorology and suggested by various authors, done by comparing EC Sensible Heat and measured by SLS through the use of an iterative determination of Monin–Obukhov parameters. A comparison of the SLS-measured structure parameter of air temperature CT2 corrected for β and uncorrected was carried out, with the results showing good correspondence but with a slight bias indicating that not correcting SLS measurements of CT2 for β would also result in a slight bias in H. Eddy covari...
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Sensible Heat Flux by surface layer scintillometry and eddy covariance over a mixed grassland community as affected by bowen ratio and most formulations for unstable conditions
Journal of Hydrometeorology, 2009Co-Authors: George O. Odhiambo, M J SavageAbstract:Abstract Measurements of Sensible Heat Flux for an extended period for unstable conditions using surface layer scintillometry (SLS) and eddy covariance (EC) and supplemented by Bowen ratio measurements for a mixed grassland community on the eastern seaboard of South Africa are presented. Measurements of SLS Sensible Heat Flux density were compared with those obtained using EC for a wide range of Bowen ratio (β). Also presented is an analysis of the different forms of the Monin–Obukhov similarity theory (MOST) functions used in micrometeorology and suggested by various authors, done by comparing EC Sensible Heat and measured by SLS through the use of an iterative determination of Monin–Obukhov parameters. A comparison of the SLS-measured structure parameter of air temperature CT2 corrected for β and uncorrected was carried out, with the results showing good correspondence but with a slight bias indicating that not correcting SLS measurements of CT2 for β would also result in a slight bias in H. Eddy covari...
F Castellvi - One of the best experts on this subject based on the ideXlab platform.
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daytime Sensible Heat Flux estimation over heterogeneous surfaces using multitemporal land surface temperature observations
Water Resources Research, 2016Co-Authors: F Castellvi, Carmelo Cammalleri, Giuseppe Ciraolo, Antonino Maltese, F RossiAbstract:Equations based on surface renewal (SR) analysis to estimate the Sensible Heat Flux (H) require as input the mean ramp amplitude and period observed in the ramp-like pattern of the air temperature measured at high frequency. A SR-based method to estimate Sensible Heat Flux (HSR-LST) requiring only low-frequency measurements of the air temperature, horizontal mean wind speed, and land-surface temperature as input was derived and tested under unstable conditions over a heterogeneous canopy (olive grove). HSR-LST assumes that the mean ramp amplitude can be inferred from the difference between land-surface temperature and mean air temperature through a linear relationship and that the ramp frequency is related to a wind shear scale characteristic of the canopy flow. The land-surface temperature was retrieved by integrating in situ sensing measures of thermal infrared energy emitted by the surface. The performance of HSR-LST was analyzed against Flux tower measurements collected at two heights (close to and well above the canopy top). Crucial parameters involved in HSR-LST, which define the above mentioned linear relationship, were explained using the canopy height and the land surface temperature observed at sunrise and sunset. Although the olive grove can behave as either an isothermal or anisothermal surface, HSR-LST performed close to H measured using the eddy covariance and the Bowen ratio energy balance methods. Root mean square differences between HSR-LST and measured H were of about 55 W m−2. Thus, by using multitemporal thermal acquisitions, HSR-LST appears to bypass inconsistency between land surface temperature and the mean aerodynamic temperature. The one-source bulk transfer formulation for estimating H performed reliable after calibration against the eddy covariance method. After calibration, the latter performed similar to the proposed SR-LST method.
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Sensible Heat Flux estimates using two different methods based on surface renewal analysis a study case over an orange orchard in sicily
Agricultural and Forest Meteorology, 2012Co-Authors: F Castellvi, Simona Consoli, Rita PapaAbstract:Abstract An experiment was carried out over a mature orange orchard to evaluate the reliability of two methods based on surface renewal, SR, analysis, SR1 and SR2, to estimate Sensible Heat Flux, H . After calibration, the method SR1 only requires as input the air temperature measured at high frequency. However, method SR2 requires air temperature measurements taken at high frequency, the mean and turbulent standard deviation of the horizontal wind speed, the leaf area index, the canopy height and the vertical extent (m) of the foliage. Methods SR1 and SR2 operated at the canopy top, z = 4 m. The H measured using the eddy covariance, EC, method operating at height slightly higher than twice the canopy height, z = 8 m, was taken as a reference, H EC_8 m . For completeness, because the method SR1 may also operate well above the canopy, its performance was also analyzed at z = 8 m, and another EC system was deployed close to the canopy top at z = 4 m, H EC_4 m . For calibration, three periods of 15 days were selected. For method SR1, regardless the height at which operated, it is shown that calibration was dependent on weather conditions, including daily and seasonal patterns. Therefore, in contrast to other experiments that recommended application of method SR1, this study questions its reliability. For method SR2, calibration was the same for each calibration period. Validation was made for three periods of three months each. In relation to H EC_8 m , regardless of the validation period SR2 was closer than SR1 and it was less biased than H EC_4 m . Because reliability is mandatory for method selection SR2 is recommended over SR1 and it could be considered to fill gaps of the EC method for samples affected by flow distortion.
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a new procedure based on surface renewal analysis to estimate Sensible Heat Flux a case study over grapevines
Journal of Hydrometeorology, 2010Co-Authors: F Castellvi, R L SnyderAbstract:Abstract Grapevines are grown on a range of soils and in different climates. Depending on the desired final product and method of harvesting, the trellis system, and hence vineyard architecture, varies dramatically. Consequently, the crop coefficients used to estimate vineyard evapotranspiration from reference evapotranspiration are less universal than for other crops. Evapotranspiration measurements are often limited because of a lack of fetch and unavailability of vine parameters required as input. In this paper, a new procedure based on surface renewal (SR) analysis was derived to estimate Sensible Heat Flux over the grapevines. A two-dimensional sonic anemometer operating close to the canopy can provide the inputs required to estimate the Sensible Heat Flux and the work of expansion of the air parcels under constant pressure. Regardless of the stability conditions, the SR estimates were comparable to those determined using the eddy covariance (EC) method providing a root-mean-square error of 14 W m−2 ...
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on the performance of surface renewal analysis to estimate Sensible Heat Flux over two growing rice fields under the influence of regional advection
Journal of Hydrology, 2009Co-Authors: F Castellvi, Richard L SnyderAbstract:Summary High-frequency temperature data were recorded at one height and they were used in Surface Renewal (SR) analysis to estimate Sensible Heat Flux during the full growing season of two rice fields located north–northeast of Colusa, CA (in the Sacramento Valley). One of the fields was seeded into a flooded paddy and the other was drill seeded before flooding. To minimize fetch requirements, the measurement height was selected to be close to the maximum expected canopy height. The roughness sub-layer depth was estimated to discriminate if the temperature data came from the inertial or roughness sub-layer. The equation to estimate the roughness sub-layer depth was derived by combining simple mixing-length theory, mixing-layer analogy, equations to account for stable atmospheric surface layer conditions, and semi-empirical canopy–architecture relationships. The potential for SR analysis as a method that operates in the full surface boundary layer was tested using data collected over growing vegetation at a site influenced by regional advection of Sensible Heat Flux. The inputs used to estimate the Sensible Heat Fluxes included air temperature sampled at 10 Hz, the mean and variance of the horizontal wind speed, the canopy height, and the plant area index for a given intermediate height of the canopy. Regardless of the stability conditions and measurement height above the canopy, Sensible Heat Flux estimates using SR analysis gave results that were similar to those measured with the eddy covariance method. Under unstable cases, it was shown that the performance was sensitive to estimation of the roughness sub-layer depth. However, an expression was provided to select the crucial scale required for its estimation.
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Sensible Heat Flux estimates using surface renewal analysis a study case over a peach orchard
Agricultural and Forest Meteorology, 2009Co-Authors: F Castellvi, R L SnyderAbstract:This paper reports on an experiment over a peach orchard to study the reliability of surface renewal, SR, analysis for estimating Sensible Heat Flux. The peach orchard was located within the San Joaquin Valley near Parlier, CA, where clear skies, high summer temperatures, light winds, no rainfall and regional advection were the typical weather conditions. To account for the climate characteristics, the roughness sub-layer depth was estimated half-hourly. A model based on a mixing-length theory for momentum combined with mixing-layer analogy was derived and coupled with SR analysis. Roughness sub-layer estimates indicated that the top of the roughness sub-layer was oscillating above and below the measurement height. Accordingly, SR analysis was challenged as a method to be applied at a fixed height above the canopy top. Regardless of the atmospheric surface boundary-layer stability, Sensible Heat Flux estimates were close to those determined by the eddy covariance method.
George O. Odhiambo - One of the best experts on this subject based on the ideXlab platform.
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Sensible Heat Flux by surface layer scintillometry and eddy covariance over a mixed grassland community as affected by bowen ratio and most formulations for unstable conditions
Journal of Hydrometeorology, 2009Co-Authors: George O. Odhiambo, M J SavageAbstract:Abstract Measurements of Sensible Heat Flux for an extended period for unstable conditions using surface layer scintillometry (SLS) and eddy covariance (EC) and supplemented by Bowen ratio measurements for a mixed grassland community on the eastern seaboard of South Africa are presented. Measurements of SLS Sensible Heat Flux density were compared with those obtained using EC for a wide range of Bowen ratio (β). Also presented is an analysis of the different forms of the Monin–Obukhov similarity theory (MOST) functions used in micrometeorology and suggested by various authors, done by comparing EC Sensible Heat and measured by SLS through the use of an iterative determination of Monin–Obukhov parameters. A comparison of the SLS-measured structure parameter of air temperature CT2 corrected for β and uncorrected was carried out, with the results showing good correspondence but with a slight bias indicating that not correcting SLS measurements of CT2 for β would also result in a slight bias in H. Eddy covari...
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Sensible Heat Flux by surface layer scintillometry and eddy covariance over a mixed grassland community as affected by bowen ratio and most formulations for unstable conditions
Journal of Hydrometeorology, 2009Co-Authors: George O. Odhiambo, M J SavageAbstract:Abstract Measurements of Sensible Heat Flux for an extended period for unstable conditions using surface layer scintillometry (SLS) and eddy covariance (EC) and supplemented by Bowen ratio measurements for a mixed grassland community on the eastern seaboard of South Africa are presented. Measurements of SLS Sensible Heat Flux density were compared with those obtained using EC for a wide range of Bowen ratio (β). Also presented is an analysis of the different forms of the Monin–Obukhov similarity theory (MOST) functions used in micrometeorology and suggested by various authors, done by comparing EC Sensible Heat and measured by SLS through the use of an iterative determination of Monin–Obukhov parameters. A comparison of the SLS-measured structure parameter of air temperature CT2 corrected for β and uncorrected was carried out, with the results showing good correspondence but with a slight bias indicating that not correcting SLS measurements of CT2 for β would also result in a slight bias in H. Eddy covari...
H A R De Bruin - One of the best experts on this subject based on the ideXlab platform.
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comparison of Sensible Heat Flux estimates using avhrr with scintillometer measurements over semi arid grassland in northwest mexico
Agricultural and Forest Meteorology, 2000Co-Authors: Christopher J Watts, A Chehbouni, Yann Kerr, Julio Cesar Rodriguez, O K Hartogensis, H A R De BruinAbstract:The problems associated with the validation of satellite-derived estimates of the surface Fluxes are discussed and the possibility of using the large aperture scintillometer is investigated. Simple models are described to derive surface temperature and Sensible Heat Flux from the advanced very high resolution radiometer (AVHRR). Data were collected over an extensive site of semi-arid grassland in northwest Mexico during the summer of 1997 as part of the semi-arid land-surface-atmosphere (SALSA) program. Comparison of surface temperature derived from AVHRR with that derived from a ground-based infrared thermometer showed an RMSE of around 2°C, while estimates of Sensible Heat Flux derived from AVHRR compared well with measurements using either eddy correlation or a large aperture scintillometer.
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estimation of area average Sensible Heat Flux using a large aperture scintillometer during the semi arid land surface atmosphere salsa experiment
Water Resources Research, 1999Co-Authors: A Chehbouni, Yann Kerr, Christopher J Watts, O K Hartogensis, David C Goodrich, Russell L Scott, John P Schieldge, W J Shuttleworth, G Dedieu, H A R De BruinAbstract:The use of a large-aperture scintillometer to estimate Sensible Heat Flux has been successfully tested by several investigators. Most of these investigations, however, have been confined to homogeneous or to sparse with single vegetation-type surfaces. The use of the scintillometer over surfaces made up of contrasting vegetation types is problematic because it requires estimates of effective roughness length and effective displacement height in order to derive area-average Sensible Heat from measurements of the refractive index. In this study an approach based on a combination of scintillometer measurements and an aggregation scheme has been used to derive area-average Sensible Heat Flux over a transect spanning two adjacent and contrasting vegetation patches: grass and mesquite. The performance of this approach has been assessed using data collected during the 1997 Semi-Arid Land-Surface-Atmosphere field campaign. The results show that the combined approach performed remarkably well, and the correlation coefficient between measured and simulated area-average Sensible Heat Flux was ∼0.95. This is of interest because this approach offers a reliable means for validating remotely sensed estimates of surface Fluxes at comparable spatial scales.
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Sensible Heat Flux radiometric surface temperature relationship for eight semiarid areas
Journal of Applied Meteorology, 1994Co-Authors: J B Stewart, William P. Kustas, K S Humes, W D Nichols, M S Moran, H A R De BruinAbstract:Measurements of Sensible Heat Flux, radiometric surface temperature, air temperature, and wind speed made at eight semiarid rangeland sites were used to investigate the Sensible Heat Flux-aerodynamic resistance relationship. The individual sites covered a wide range of vegetation (0.1-4 m tall) and cover (3%-95% bare soil) conditions. Mean values of k/B, a quantity related to the resistance of Heat versus momentum transfer at the surface, for the individual sites varied between 3.5 and 12.5. A preliminary test of the utility of an excess resistance based on the mean value of k/B showed that the difference between the mean estimated and measured Sensible Heat Fluxes varied +/- 60 W/sq m for the eight semiarid sites. For the eight sites the values of k/B were plotted against the roughness Reynolds number. The plot showed considerable scatter with values ranging between and beyond the theoretical curves for bluff rough and permeable rough surfaces.
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Estimation of the Sensible Heat Flux of a semi-arid area using surface radiative temperature measurements
Boundary-Layer Meteorology, 1993Co-Authors: W. Kohsiek, H A R De Bruin, H. The, B. HurkAbstract:In the framework of an international field program for the study of semi-arid areas, observations were done in the region called ‘La Crau’ in southern France. In this paper, the use of the surface radiative temperature for the determination of the Sensible Heat Flux is addressed. We found that, once proper values of the roughness length of momentum ( z _0) and Heat ( z _0h) are set, the Sensible Heat Flux can be reliably predicted with a one-layer resistance model using standard observations of wind speed and air temperature, together with the surface temperature. The latter quantity has to be known with a precision better than ±2°C. From our observations, the value of the parameter B ^−1≡ k ^−1 In ( z _0 z _0h) was found to be 9.2, which falls between values quoted by Brutsaert (1982) for grass and bluff bodies.
Pierre Durand - One of the best experts on this subject based on the ideXlab platform.
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Potential and Limitations in Estimating Sensible-Heat-Flux Profiles from Consecutive Temperature Profiles Using Remotely-Piloted Aircraft Systems
Boundary-Layer Meteorology, 2019Co-Authors: Line Båserud, Marius O. Jonassen, Maria A. Jiménez, Phillip B Chilson, Timothy A Bonin, Joachim Reuder, Pierre DurandAbstract:Profiles of the Sensible Heat Flux are key to understanding atmospheric-boundary-layer (ABL) structure and development. Based on temperature profiling by a remotely-piloted aircraft system (RPAS), the Small Unmanned Meteorological Observer (SUMO) platform, during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign, 108 Heat-Flux profiles are estimated using a simplified version of the prognostic equation for potential temperature $$\theta $$ θ that relates the tendency in $$\theta $$ θ to the Flux divergence over the time span between two consecutive flights. We validate for the first time RPAS-based Heat-Flux profiles against a network of 12 ground-based eddy-covariance stations (2–60 m above ground), in addition to a comparison with Fluxes from a manned aircraft and a tethered balloon, enabling the detailed investigation of the potential and limitations related to this technique for obtaining Fluxes from RPAS platforms. We find that appropriate treatment of horizontal advection is crucial for obtaining realistic Flux values, and present correction methods specific to the state of the ABL. Advection from a mesoscale model is also tested as another correction method. The SUMO Heat-Flux estimates with appropriate corrections compare well with the reference measurements, with differences in the performance depending on the time of day, since the evening period shows the best results (94 $$\%$$ % within the spread of ground stations), and the afternoon period shows the poorest results (63 $$\%$$ % within the spread). The diurnal cycle of the Heat Flux is captured by the SUMO platform for several days, with the Flux values from the manned aircraft and tethered balloon coinciding well with those from the SUMO platform.
