Radiation Balance

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Michael Lehning - One of the best experts on this subject based on the ideXlab platform.

  • explicit validation of a surface shortwave Radiation Balance model over snow covered complex terrain
    Journal of Geophysical Research, 2010
    Co-Authors: N Helbig, Henning Lowe, Bernhard Mayer, Michael Lehning
    Abstract:

    A model that computes the surface Radiation Balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky Radiation is determined from observations of incident global Radiation, air temperature, and relative humidity at a single measurement location. Incident Radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky Radiation for all sky conditions are obtained by decomposing the measured global Radiation value. Spatial incident Radiation values under all atmospheric conditions are computed by adjusting the spatial Radiation values obtained from the parametric model with the Radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected Radiation. Validations of the shortwave Radiation Balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual Radiation components is performed with highA¢Â€Âquality measurements. A new measurement setup was designed to determine terrain reflected Radiation. There is good agreement between the measurements and the modeled terrain reflected Radiation values as well as with incident Radiation values. A comparison of the model with a fully threeA¢Â€Âdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values

  • Explicit validation of a surface shortwave Radiation Balance model over snow‐covered complex terrain
    Journal of Geophysical Research, 2010
    Co-Authors: N Helbig, Henning Lowe, Bernhard Mayer, Michael Lehning
    Abstract:

    A model that computes the surface Radiation Balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky Radiation is determined from observations of incident global Radiation, air temperature, and relative humidity at a single measurement location. Incident Radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky Radiation for all sky conditions are obtained by decomposing the measured global Radiation value. Spatial incident Radiation values under all atmospheric conditions are computed by adjusting the spatial Radiation values obtained from the parametric model with the Radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected Radiation. Validations of the shortwave Radiation Balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual Radiation components is performed with highA¢Â€Âquality measurements. A new measurement setup was designed to determine terrain reflected Radiation. There is good agreement between the measurements and the modeled terrain reflected Radiation values as well as with incident Radiation values. A comparison of the model with a fully threeA¢Â€Âdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values

  • radiosity approach for the shortwave surface Radiation Balance in complex terrain
    Journal of the Atmospheric Sciences, 2009
    Co-Authors: N Helbig, Henning Lowe, Michael Lehning
    Abstract:

    The influence of topography on the Radiation Balance in complex terrain has so far been investigated either with very simple or very sophisticated approaches that are limited, respectively, by an uncontrolled spatial representation of radiative fluxes or heavy computational efforts. To bridge this gap in complexity, this paper proposes the radiosity approach, well known in computer graphics, to study anisotropic reflections of Radiation in complex terrain. To this end the radiosity equation is rederived in the context of three-dimensional radiative transfer. The discretized equation is solved by means of an adapted version of progressive refinement iteration. To systematically study terrain effects, the geometrical disorder provided by the topography is considered in its simplest approximation by Gaussian random fields. These model topographies capture the most important length scales of complex terrain, namely a typical elevation and a typical valley width via the variance and the correlation length of the field, respectively. The mean reflected Radiation is computed as a function of these length scales and sun elevation, thereby explicitly addressing finite system sizes and grid resolutions. A comparison with an isotropic parameterization of terrain reflections reveals that mean values are similar whereas spatial distributions vary remarkably. It is also shown that the mean reflected Radiation in real topography is reasonably well characterized by the Gaussian approximation. As a final application of the method, the effective albedo of a topography is shown to vary with sun elevation and domain-averaged albedo, leading to albedo differences up to 0.025.

Jinkyu Hong - One of the best experts on this subject based on the ideXlab platform.

  • simulation of surface Radiation Balance on the tibetan plateau
    Geophysical Research Letters, 2008
    Co-Authors: Jinkyu Hong
    Abstract:

    [1] Tibetan Plateau is vulnerable to climate changes. At the same time, an altered surface Radiation Balance on the Plateau due to its rapid development would contribute to feedback and causes of global climate changes, particularly the Asian summer monsoon. In this study, we investigated surface Radiation Balance on the Tibetan Plateau by comparative analysis of two land surface models with the in-situ observation data. Our scrutiny reveals that radiative coupling, which has been neglected over low elevation region, is important in simulating surface energy Balance on the Tibetan Plateau. For a proper assessment of surface Radiation Balance and hydrologic cycle on the Plateau, surface albedo and emissivity should be also correctly incorporated into land surface models and remote sensing algorithm.

N Helbig - One of the best experts on this subject based on the ideXlab platform.

  • explicit validation of a surface shortwave Radiation Balance model over snow covered complex terrain
    Journal of Geophysical Research, 2010
    Co-Authors: N Helbig, Henning Lowe, Bernhard Mayer, Michael Lehning
    Abstract:

    A model that computes the surface Radiation Balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky Radiation is determined from observations of incident global Radiation, air temperature, and relative humidity at a single measurement location. Incident Radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky Radiation for all sky conditions are obtained by decomposing the measured global Radiation value. Spatial incident Radiation values under all atmospheric conditions are computed by adjusting the spatial Radiation values obtained from the parametric model with the Radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected Radiation. Validations of the shortwave Radiation Balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual Radiation components is performed with highA¢Â€Âquality measurements. A new measurement setup was designed to determine terrain reflected Radiation. There is good agreement between the measurements and the modeled terrain reflected Radiation values as well as with incident Radiation values. A comparison of the model with a fully threeA¢Â€Âdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values

  • Explicit validation of a surface shortwave Radiation Balance model over snow‐covered complex terrain
    Journal of Geophysical Research, 2010
    Co-Authors: N Helbig, Henning Lowe, Bernhard Mayer, Michael Lehning
    Abstract:

    A model that computes the surface Radiation Balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky Radiation is determined from observations of incident global Radiation, air temperature, and relative humidity at a single measurement location. Incident Radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky Radiation for all sky conditions are obtained by decomposing the measured global Radiation value. Spatial incident Radiation values under all atmospheric conditions are computed by adjusting the spatial Radiation values obtained from the parametric model with the Radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected Radiation. Validations of the shortwave Radiation Balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual Radiation components is performed with highA¢Â€Âquality measurements. A new measurement setup was designed to determine terrain reflected Radiation. There is good agreement between the measurements and the modeled terrain reflected Radiation values as well as with incident Radiation values. A comparison of the model with a fully threeA¢Â€Âdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values

  • radiosity approach for the shortwave surface Radiation Balance in complex terrain
    Journal of the Atmospheric Sciences, 2009
    Co-Authors: N Helbig, Henning Lowe, Michael Lehning
    Abstract:

    The influence of topography on the Radiation Balance in complex terrain has so far been investigated either with very simple or very sophisticated approaches that are limited, respectively, by an uncontrolled spatial representation of radiative fluxes or heavy computational efforts. To bridge this gap in complexity, this paper proposes the radiosity approach, well known in computer graphics, to study anisotropic reflections of Radiation in complex terrain. To this end the radiosity equation is rederived in the context of three-dimensional radiative transfer. The discretized equation is solved by means of an adapted version of progressive refinement iteration. To systematically study terrain effects, the geometrical disorder provided by the topography is considered in its simplest approximation by Gaussian random fields. These model topographies capture the most important length scales of complex terrain, namely a typical elevation and a typical valley width via the variance and the correlation length of the field, respectively. The mean reflected Radiation is computed as a function of these length scales and sun elevation, thereby explicitly addressing finite system sizes and grid resolutions. A comparison with an isotropic parameterization of terrain reflections reveals that mean values are similar whereas spatial distributions vary remarkably. It is also shown that the mean reflected Radiation in real topography is reasonably well characterized by the Gaussian approximation. As a final application of the method, the effective albedo of a topography is shown to vary with sun elevation and domain-averaged albedo, leading to albedo differences up to 0.025.

Henning Lowe - One of the best experts on this subject based on the ideXlab platform.

  • explicit validation of a surface shortwave Radiation Balance model over snow covered complex terrain
    Journal of Geophysical Research, 2010
    Co-Authors: N Helbig, Henning Lowe, Bernhard Mayer, Michael Lehning
    Abstract:

    A model that computes the surface Radiation Balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky Radiation is determined from observations of incident global Radiation, air temperature, and relative humidity at a single measurement location. Incident Radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky Radiation for all sky conditions are obtained by decomposing the measured global Radiation value. Spatial incident Radiation values under all atmospheric conditions are computed by adjusting the spatial Radiation values obtained from the parametric model with the Radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected Radiation. Validations of the shortwave Radiation Balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual Radiation components is performed with highA¢Â€Âquality measurements. A new measurement setup was designed to determine terrain reflected Radiation. There is good agreement between the measurements and the modeled terrain reflected Radiation values as well as with incident Radiation values. A comparison of the model with a fully threeA¢Â€Âdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values

  • Explicit validation of a surface shortwave Radiation Balance model over snow‐covered complex terrain
    Journal of Geophysical Research, 2010
    Co-Authors: N Helbig, Henning Lowe, Bernhard Mayer, Michael Lehning
    Abstract:

    A model that computes the surface Radiation Balance for all sky conditions in complex terrain is presented. The spatial distribution of direct and diffuse sky Radiation is determined from observations of incident global Radiation, air temperature, and relative humidity at a single measurement location. Incident Radiation under cloudless sky is spatially derived from a parameterization of the atmospheric transmittance. Direct and diffuse sky Radiation for all sky conditions are obtained by decomposing the measured global Radiation value. Spatial incident Radiation values under all atmospheric conditions are computed by adjusting the spatial Radiation values obtained from the parametric model with the Radiation components obtained from the decomposition model at the measurement site. Topographic influences such as shading are accounted for. The radiosity approach is used to compute anisotropic terrain reflected Radiation. Validations of the shortwave Radiation Balance model are presented in detail for a day with cloudless sky. For a day with overcast sky a first validation is presented. Validation of a section of the horizon line as well as of individual Radiation components is performed with highA¢Â€Âquality measurements. A new measurement setup was designed to determine terrain reflected Radiation. There is good agreement between the measurements and the modeled terrain reflected Radiation values as well as with incident Radiation values. A comparison of the model with a fully threeA¢Â€Âdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values

  • radiosity approach for the shortwave surface Radiation Balance in complex terrain
    Journal of the Atmospheric Sciences, 2009
    Co-Authors: N Helbig, Henning Lowe, Michael Lehning
    Abstract:

    The influence of topography on the Radiation Balance in complex terrain has so far been investigated either with very simple or very sophisticated approaches that are limited, respectively, by an uncontrolled spatial representation of radiative fluxes or heavy computational efforts. To bridge this gap in complexity, this paper proposes the radiosity approach, well known in computer graphics, to study anisotropic reflections of Radiation in complex terrain. To this end the radiosity equation is rederived in the context of three-dimensional radiative transfer. The discretized equation is solved by means of an adapted version of progressive refinement iteration. To systematically study terrain effects, the geometrical disorder provided by the topography is considered in its simplest approximation by Gaussian random fields. These model topographies capture the most important length scales of complex terrain, namely a typical elevation and a typical valley width via the variance and the correlation length of the field, respectively. The mean reflected Radiation is computed as a function of these length scales and sun elevation, thereby explicitly addressing finite system sizes and grid resolutions. A comparison with an isotropic parameterization of terrain reflections reveals that mean values are similar whereas spatial distributions vary remarkably. It is also shown that the mean reflected Radiation in real topography is reasonably well characterized by the Gaussian approximation. As a final application of the method, the effective albedo of a topography is shown to vary with sun elevation and domain-averaged albedo, leading to albedo differences up to 0.025.

S R Green - One of the best experts on this subject based on the ideXlab platform.

  • Radiation Balance transpiration and photosynthesis of an isolated tree
    Agricultural and Forest Meteorology, 1993
    Co-Authors: S R Green
    Abstract:

    Abstract The Radiation Balance of an isolated walnut tree was measured using an experimental Whirligig device. The total amount of all-wave Radiation absorbed by the tree canopy was used to estimate transpiration rates using a Penman-Monteith model. The results compared favourably with tree water use, measured by the heat-pulse technique. The total amount of photosynthetically active Radiation (PAR) absorbed by the tree canopy was combined with a photosynthetic light response curve to estimate net photosynthesis rates. The results compare favourably with published data from other tree canopies. Daily energy Balance calculations showed that on average, about two-thirds of the total radiant energy absorbed by the tree canopy was dissipated as latent heat in the form of transpiration. The dominant environmental variable influencing transpiration was the vapour pressure deficit of the air. Almost two-thirds of the net latent heat flux was attributable to the vapour pressure deficit component, with the remainder owing to the Radiation component. Daily transpiration-assimilation ratios varied from day to day in response to changing environmental conditions, but generally decreased with increasing net photosynthesis and with increasing transpiration. This appears to be the first time that such a direct measurement of the energy Balance and photosynthesis of a single tree has been made.