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Michael Lehning - One of the best experts on this subject based on the ideXlab platform.
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explicit validation of a surface shortwave Radiation balance model over snow covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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Explicit validation of a surface shortwave Radiation balance model over snow‐covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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radiosity approach for the shortwave surface Radiation balance in complex terrain
Journal of the Atmospheric Sciences, 2009Co-Authors: Natalie Helbig, Henning Lowe, Michael LehningAbstract: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.
Natalie Helbig - One of the best experts on this subject based on the ideXlab platform.
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explicit validation of a surface shortwave Radiation balance model over snow covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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Explicit validation of a surface shortwave Radiation balance model over snow‐covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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radiosity approach for the shortwave surface Radiation balance in complex terrain
Journal of the Atmospheric Sciences, 2009Co-Authors: Natalie Helbig, Henning Lowe, Michael LehningAbstract: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.
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explicit validation of a surface shortwave Radiation balance model over snow covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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Explicit validation of a surface shortwave Radiation balance model over snow‐covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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radiosity approach for the shortwave surface Radiation balance in complex terrain
Journal of the Atmospheric Sciences, 2009Co-Authors: Natalie Helbig, Henning Lowe, Michael LehningAbstract: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.
Bernhard Mayer - One of the best experts on this subject based on the ideXlab platform.
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explicit validation of a surface shortwave Radiation balance model over snow covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
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Explicit validation of a surface shortwave Radiation balance model over snow‐covered complex terrain
Journal of Geophysical Research, 2010Co-Authors: Natalie Helbig, Henning Lowe, Bernhard Mayer, Michael LehningAbstract: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¢ÂÂquality 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¢ÂÂdimensional radiative transfer Monte Carlo model is presented. That validation reveals a good agreement between modeled Radiation values
Takayuki Kaneko - One of the best experts on this subject based on the ideXlab platform.
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Testing the accuracy of solar-Reflected Radiation corrections applied during satellite shortwave infrared thermal analysis of active volcanoes
Journal of Geophysical Research, 2001Co-Authors: Martin J. Wooster, Takayuki KanekoAbstract:Shortwave infrared (SWIR) satellite imagery is frequently used to study thermal emission from active volcanoes. When using daytime SWIR observations it is necessary to first isolate the thermally emitted signal component, principally by subtracting contributions due to solar-Reflected Radiation. Two differing approaches have been used: (1) A “mean” approach based on the average SWIR reflectance of the nonthermally anomalous volcanic background, and (2) a “per-pixel” approach which estimates the SWIR reflectance of each pixel using a measure of their near infrared reflectance. We assess the accuracy of these using near-coincident daytime and nighttime Landsat Thematic Mapper (TM) imagery of the active lava dome of Unzen Volcano. Using the nighttime data as a reference we find the most commonly applied mean daytime correction approach to be seriously inadequate, returning results for thermally radiant area 81–94% smaller than the nighttime values. The per-pixel correction method appears somewhat more effective but still provides values 47–61% smaller than the reference data set. Daytime underestimation of total SWIR thermal spectral radiance is less severe than that of total thermally radiant area because it is primarily pixels having low thermal signals that pose a problem for the daytime approaches. Total thermal spectral radiance is underestimated by 52–79% using the daytime data with the mean correction approach, and by 28–59% with the per-pixel approach. When applying the TM “dual-band” technique to determine subpixel hot spot temperatures from the SWIR thermal signals, we find that surfaces cooler than 400°C are poorly represented in the daytime retrievals. However, when using the per-pixel daytime data correction method the distribution of retrieved hot spots >400°C corresponds quite well to the pattern derived via nighttime imagery. Due to the significant parameter underestimation found to be inherent when using daytime data, this study further indicates the value of nighttime observations to volcanic SWIR thermal studies. If daytime data are used, then we recommend use of the per-pixel solar-Reflected Radiation correction method but would advise caution when quantitatively interpreting the derived thermal parameters, at least at andesitic and dacitic volcanoes. It is possible that daytime retrievals may be more robust at basaltic volcanoes due to their characteristic higher magmatic temperatures and lower surface reflectances.