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H. Mayer - One of the best experts on this subject based on the ideXlab platform.
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Net Radiation balance for two forested slopes on opposite sides of a valley
International Journal of Biometeorology, 2005Co-Authors: T. Holst, Janmichael Rost, H. MayerAbstract:Measurements of the Net Radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming Radiation was adjusted according to the slope’s angle to convert horizontally measured Radiation data into surface-parallel Radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal Radiation fluxes were available, the calculation of surface-parallel Radiation fluxes from the horizontally recorded Net Radiation components were compared with measured values. The Net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the Net Radiation balance. In June, when the elevation of the sun is highest, incoming solar Radiation K↓ received on the NE-slope was 9% lower than K↓ received on the SW-slope. During the winter months, the differences were much greater and incoming solar Radiation to the NE-slope was 50% of that to the SW-slope. Due to the differing solar irradiance, Net Radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave Radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the Net Radiation balance between the slopes are important for the vegetation.
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Net Radiation balance for two forested slopes on opposite sides of a valley
International Journal of Biometeorology, 2005Co-Authors: T. Holst, Janmichael Rost, H. MayerAbstract:Measurements of the Net Radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming Radiation was adjusted according to the slope’s angle to convert horizontally measured Radiation data into surface-parallel Radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal Radiation fluxes were available, the calculation of surface-parallel Radiation fluxes from the horizontally recorded Net Radiation components were compared with measured values. The Net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the Net Radiation balance. In June, when the elevation of the sun is highest, incoming solar Radiation K↓ received on the NE-slope was 9% lower than K↓ received on the SW-slope. During the winter months, the differences were much greater and incoming solar Radiation to the NE-slope was 50% of that to the SW-slope. Due to the differing solar irradiance, Net Radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave Radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the Net Radiation balance between the slopes are important for the vegetation.
Mukesh Kumar - One of the best experts on this subject based on the ideXlab platform.
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How Net Radiation on Forested Snowpack Changes across a Latitudinal Gradient
2019Co-Authors: Bijan Seyednasrollah, Mukesh KumarAbstract:Radiation is the major driver of snowmelt, and hence its estimation is critically important. Net Radiation reaching the forest floor is influenced by vegetation density. Previous studies in mid-latitude conifer forests have confirmed that Net Radiation decreases and then subsequently increases with increasing vegetation density, for clear sky conditions. This leads to existence of a Net Radiation minimum at an intermediate vegetation density. With increasing cloud cover, the minimum Radiation shifts toward lower densities, sometimes resulting in a monotonically increasing Radiation with vegetation density. The Net Radiation trend, however, is expected to change across sites, affecting the magnitude and timing of individual Radiation components. This research explores the variability of Net Radiation on snow-covered forest floor for different vegetation densities along a latitudinal gradient. We especially investigate how the magnitude of minimum/maximum Radiation and the corresponding vegetation density change with the site geographical location. To evaluate these, the Net Radiation is evaluated using the Forest Radiation Model at six different locations in predominantly white spruce (Picea glauca) canopy cover across North America, ranging from 45 to 66°N latitudes. Results show that the variation of Net Radiation with vegetation density considerably varies with latitude. In higher latitude forests, the magnitude of Net Radiation is generally smaller, and the minimum Radiation is exhibited at relatively sparser vegetation densities, under clear sky conditions. For interspersed cloudy sky conditions, Net Radiation non-monotonically varies with latitude across the sites, depending on the seasonal sky cloudiness and air temperature. Latitudinal sensitivity of Net Radiation is lower on north-facing hillslopes than on south-facing sites.
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Net Radiation in a snow‐covered discontinuous forest gap for a range of gap sizes and topographic configurations
Journal of Geophysical Research, 2014Co-Authors: Bijan Seyednasrollah, Mukesh KumarAbstract:Estimating Net Radiation on the forest floor is crucial for predicting snowmelt recharge and for quantifying water yield from snow-dominated forested watersheds. However, complex characteristics of Radiation transfer in discontinuous forest gaps make this estimation challenging. This study quantifies Net Radiation within a forest gap for a range of gap sizes, slopes and aspects, and meteorological conditions. The spatial distribution of Net Radiation in the gap is found to be heterogeneous with southern and northern areas of the gap receiving minimum and maximum energy amounts, respectively. At a midlatitude site and for completely clear sky conditions in the snow season, results suggest that Net Radiation in the forest gap is minimum for gaps of size equal to half of the surrounding tree height. In contrast, when sky cloudiness in the snow season is considered, Net Radiation shows a monotonically increasing trend with gap size. Slope and aspect of forest gap floor also impact the Net Radiation and its variation with gap size. Net Radiation is largest and smallest on steep south-facing and north-facing slopes, respectively. Variation of Net Radiation with slope and aspect is largest for larger gaps. Results also suggest that Net Radiation in north-facing forest gaps is larger than in open areas for a longer duration in the snow season than in forest gaps on flat and south-facing slopes. Since Net Radiation directly affects melt recharge and evaporation, these findings have implications on forest and water management, wildfire hazard, and forest health.
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Net Radiation in a snow covered discontinuous forest gap for a range of gap sizes and topographic configurations
Journal of Geophysical Research, 2014Co-Authors: Bijan Seyednasrollah, Mukesh KumarAbstract:Estimating Net Radiation on the forest floor is crucial for predicting snowmelt recharge and for quantifying water yield from snow-dominated forested watersheds. However, complex characteristics of Radiation transfer in discontinuous forest gaps make this estimation challenging. This study quantifies Net Radiation within a forest gap for a range of gap sizes, slopes and aspects, and meteorological conditions. The spatial distribution of Net Radiation in the gap is found to be heterogeneous with southern and northern areas of the gap receiving minimum and maximum energy amounts, respectively. At a midlatitude site and for completely clear sky conditions in the snow season, results suggest that Net Radiation in the forest gap is minimum for gaps of size equal to half of the surrounding tree height. In contrast, when sky cloudiness in the snow season is considered, Net Radiation shows a monotonically increasing trend with gap size. Slope and aspect of forest gap floor also impact the Net Radiation and its variation with gap size. Net Radiation is largest and smallest on steep south-facing and north-facing slopes, respectively. Variation of Net Radiation with slope and aspect is largest for larger gaps. Results also suggest that Net Radiation in north-facing forest gaps is larger than in open areas for a longer duration in the snow season than in forest gaps on flat and south-facing slopes. Since Net Radiation directly affects melt recharge and evaporation, these findings have implications on forest and water management, wildfire hazard, and forest health.
Shunlin Liang - One of the best experts on this subject based on the ideXlab platform.
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empirical estimation of daytime Net Radiation from shortwave Radiation and ancillary information
Agricultural and Forest Meteorology, 2015Co-Authors: Bo Jiang, Shunlin Liang, Yi Zhang, Georg Wohlfahrt, Altaf Arain, Alessandro Cescatti, T Georgiadis, Kun Jia, Gerard KielyAbstract:Abstract All-wave Net surface Radiation is greatly needed in various scientific research and applications. Satellite data have been used to estimate incident shortwave Radiation, but hardly to estimate all-wave Net Radiation due to the inference of clouds on longwave Radiation. A practical solution is to estimate all-wave Net Radiation empirically from shortwave Radiation and other ancillary information. Since existing models were developed using a limited number of ground observations, a comprehensive evaluation of these models using a global Network of representative measurements is urgently required. In this study, we developed a new day-time Net Radiation estimation model and evaluated it against seven commonly used existing models using Radiation measurements obtained from 326 sites around the world from 1991 to 2010. MERRA re-analysis products from which the meteorological data were derived and remotely sensed products during the same period were also used. Model evaluations were performed in both global mode (all data were used to fit the models) and conditional mode (the data were divided into four subsets based on the surface albedo and vegetation index, and the models were fitted separately). Besides, the factors (i.e., albedo, air temperature, and NDVI) that may impact the estimation of all-wave Net Radiation were also extensively explored. Based on these evaluations, the fitting RMSE of the new developed model was approximately 40.0 Wm −2 in the global mode and varied between 18.2 and 54.0 Wm −2 in the conditional mode. We found that it is better to use Net shortwave Radiation (including surface albedo) than the incident shortwave Radiation nearly in all models. Overall, the new model performed better than other existing linear models.
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Estimating the Optimal Broadband Emissivity Spectral Range for Calculating Surface Longwave Net Radiation
IEEE Geoscience and Remote Sensing Letters, 2013Co-Authors: Jie Cheng, Shunlin Liang, Yunjun Yao, Xiaotong ZhangAbstract:Surface broadband emissivity (BBE) in the thermal infrared spectrum is essential for calculating the surface total longwave Net Radiation in land surface models. However, almost all narrowband emissivities estimated from satellite observations are in the 3-14-μm spectral region. Previous studies converted these narrowband emissivities to BBE over different spectral ranges, such as 3-14, 8-12, 8-13.5, and 8-14 μm . Errors in the calculated total longwave Net Radiation must be quantified systematically using these BBEs. Moreover, the best spectral range for longwave Net Radiation must be determined. The key to addressing these issues is the use of the realistic emissivity spectra. By applying modern radiative transfer tools, we derived the emissivity spectra of water, snow, and minerals at 1-200 μm . Using these emissivity spectra, we first investigated the accuracy of replacing all-wavelength surface longwave Net Radiation with the surface longwave Net Radiation in the 3-100-, 4-100-, 2.5-100-, 2.5-200-, and 1-200-μm spectral domains. Surface longwave Net Radiation at 2.5-200 μm was found to be optimal, with a bias and root mean square (rms) of less than 0.928 and 0.993 W/m2, respectively. We calculated the errors when estimating surface longwave Net Radiation at 2.5-200 μm with BBE in different spectral ranges. The results show that BBE at 8-13.5 μm had the lowest error and the corresponding bias and rms were less than 0.002 and 1.453 W/m2, respectively. When the 2.5-200-μm surface longwave Net Radiation calculated by the 8-13.5-μm BBE was used to replace the all-wavelength surface longwave Net Radiation, the average bias and rms were 1.473 and 2.746 W/m2, respectively. Using the most representative emissivity spectra, we derived the conversion formulas for calculating BBE at 8-13.5 μm from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Moderate Resolution Imaging Spectrometer (MODIS) narrowband emissivity products.
T. Holst - One of the best experts on this subject based on the ideXlab platform.
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Net Radiation balance for two forested slopes on opposite sides of a valley
International Journal of Biometeorology, 2005Co-Authors: T. Holst, Janmichael Rost, H. MayerAbstract:Measurements of the Net Radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming Radiation was adjusted according to the slope’s angle to convert horizontally measured Radiation data into surface-parallel Radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal Radiation fluxes were available, the calculation of surface-parallel Radiation fluxes from the horizontally recorded Net Radiation components were compared with measured values. The Net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the Net Radiation balance. In June, when the elevation of the sun is highest, incoming solar Radiation K↓ received on the NE-slope was 9% lower than K↓ received on the SW-slope. During the winter months, the differences were much greater and incoming solar Radiation to the NE-slope was 50% of that to the SW-slope. Due to the differing solar irradiance, Net Radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave Radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the Net Radiation balance between the slopes are important for the vegetation.
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Net Radiation balance for two forested slopes on opposite sides of a valley
International Journal of Biometeorology, 2005Co-Authors: T. Holst, Janmichael Rost, H. MayerAbstract:Measurements of the Net Radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming Radiation was adjusted according to the slope’s angle to convert horizontally measured Radiation data into surface-parallel Radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal Radiation fluxes were available, the calculation of surface-parallel Radiation fluxes from the horizontally recorded Net Radiation components were compared with measured values. The Net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the Net Radiation balance. In June, when the elevation of the sun is highest, incoming solar Radiation K↓ received on the NE-slope was 9% lower than K↓ received on the SW-slope. During the winter months, the differences were much greater and incoming solar Radiation to the NE-slope was 50% of that to the SW-slope. Due to the differing solar irradiance, Net Radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave Radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the Net Radiation balance between the slopes are important for the vegetation.
Bijan Seyednasrollah - One of the best experts on this subject based on the ideXlab platform.
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How Net Radiation on Forested Snowpack Changes across a Latitudinal Gradient
2019Co-Authors: Bijan Seyednasrollah, Mukesh KumarAbstract:Radiation is the major driver of snowmelt, and hence its estimation is critically important. Net Radiation reaching the forest floor is influenced by vegetation density. Previous studies in mid-latitude conifer forests have confirmed that Net Radiation decreases and then subsequently increases with increasing vegetation density, for clear sky conditions. This leads to existence of a Net Radiation minimum at an intermediate vegetation density. With increasing cloud cover, the minimum Radiation shifts toward lower densities, sometimes resulting in a monotonically increasing Radiation with vegetation density. The Net Radiation trend, however, is expected to change across sites, affecting the magnitude and timing of individual Radiation components. This research explores the variability of Net Radiation on snow-covered forest floor for different vegetation densities along a latitudinal gradient. We especially investigate how the magnitude of minimum/maximum Radiation and the corresponding vegetation density change with the site geographical location. To evaluate these, the Net Radiation is evaluated using the Forest Radiation Model at six different locations in predominantly white spruce (Picea glauca) canopy cover across North America, ranging from 45 to 66°N latitudes. Results show that the variation of Net Radiation with vegetation density considerably varies with latitude. In higher latitude forests, the magnitude of Net Radiation is generally smaller, and the minimum Radiation is exhibited at relatively sparser vegetation densities, under clear sky conditions. For interspersed cloudy sky conditions, Net Radiation non-monotonically varies with latitude across the sites, depending on the seasonal sky cloudiness and air temperature. Latitudinal sensitivity of Net Radiation is lower on north-facing hillslopes than on south-facing sites.
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Net Radiation in a snow‐covered discontinuous forest gap for a range of gap sizes and topographic configurations
Journal of Geophysical Research, 2014Co-Authors: Bijan Seyednasrollah, Mukesh KumarAbstract:Estimating Net Radiation on the forest floor is crucial for predicting snowmelt recharge and for quantifying water yield from snow-dominated forested watersheds. However, complex characteristics of Radiation transfer in discontinuous forest gaps make this estimation challenging. This study quantifies Net Radiation within a forest gap for a range of gap sizes, slopes and aspects, and meteorological conditions. The spatial distribution of Net Radiation in the gap is found to be heterogeneous with southern and northern areas of the gap receiving minimum and maximum energy amounts, respectively. At a midlatitude site and for completely clear sky conditions in the snow season, results suggest that Net Radiation in the forest gap is minimum for gaps of size equal to half of the surrounding tree height. In contrast, when sky cloudiness in the snow season is considered, Net Radiation shows a monotonically increasing trend with gap size. Slope and aspect of forest gap floor also impact the Net Radiation and its variation with gap size. Net Radiation is largest and smallest on steep south-facing and north-facing slopes, respectively. Variation of Net Radiation with slope and aspect is largest for larger gaps. Results also suggest that Net Radiation in north-facing forest gaps is larger than in open areas for a longer duration in the snow season than in forest gaps on flat and south-facing slopes. Since Net Radiation directly affects melt recharge and evaporation, these findings have implications on forest and water management, wildfire hazard, and forest health.
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Net Radiation in a snow covered discontinuous forest gap for a range of gap sizes and topographic configurations
Journal of Geophysical Research, 2014Co-Authors: Bijan Seyednasrollah, Mukesh KumarAbstract:Estimating Net Radiation on the forest floor is crucial for predicting snowmelt recharge and for quantifying water yield from snow-dominated forested watersheds. However, complex characteristics of Radiation transfer in discontinuous forest gaps make this estimation challenging. This study quantifies Net Radiation within a forest gap for a range of gap sizes, slopes and aspects, and meteorological conditions. The spatial distribution of Net Radiation in the gap is found to be heterogeneous with southern and northern areas of the gap receiving minimum and maximum energy amounts, respectively. At a midlatitude site and for completely clear sky conditions in the snow season, results suggest that Net Radiation in the forest gap is minimum for gaps of size equal to half of the surrounding tree height. In contrast, when sky cloudiness in the snow season is considered, Net Radiation shows a monotonically increasing trend with gap size. Slope and aspect of forest gap floor also impact the Net Radiation and its variation with gap size. Net Radiation is largest and smallest on steep south-facing and north-facing slopes, respectively. Variation of Net Radiation with slope and aspect is largest for larger gaps. Results also suggest that Net Radiation in north-facing forest gaps is larger than in open areas for a longer duration in the snow season than in forest gaps on flat and south-facing slopes. Since Net Radiation directly affects melt recharge and evaporation, these findings have implications on forest and water management, wildfire hazard, and forest health.