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首页> 外文期刊>IEEE Geoscience and Remote Sensing Letters >Effects of Thermal-Infrared Emissivity Directionality on Surface Broadband Emissivity and Longwave Net Radiation Estimation
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Effects of Thermal-Infrared Emissivity Directionality on Surface Broadband Emissivity and Longwave Net Radiation Estimation

机译：热红外发射率方向性对表面宽带发射率和长波净辐射估计的影响

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摘要

Directionality is ignored in the satellite retrieval of surface thermal-infrared emissivity, which will unavoidably affect the estimates of surface broadband emissivity and surface longwave net radiation. The purpose of this work is to quantify the effects of emissivity directionality. First, three types of emissivity data are used to calculate hemispherical emissivity and the difference between directional broadband emissivity and hemispherical broadband emissivity. The emissivity directionality is highly significant, and the directional emissivity decreases with increasing view angles. A view angle within 45$^{circ}$ –60$^{circ}$ can be found whose directional emissivity is highly close to the hemispherical emissivity, and the difference between the calculated directional and hemispherical broadband emissivity is zero. The difference between the atmospheric downward radiation and blackbody radiation at surface temperature is then determined by extensive simulations. Finally, the error ranges of surface longwave net radiation are presented. If the sensor scan angle is within $pm 55^{circ}$, the error can reach as high as 17.48 and 14.05 $ hbox{W/m}^{2}$ for water and bare ice, respectively; the error is less than 2.74 $hbox{W/m}^{2}$ for snow with different radii; the error can reach 4.11 $hbox{W/m}^{2}$ for sun crust; the error is less than 5.14 $hbox{W/m}^{2}$ for minerals, sand, slime and gravel; and clay has the smallest error at 1.02 $hbox{- /m}^{2}$.
机译：卫星检索表面热红外发射率时会忽略方向性，这将不可避免地影响表面宽带发射率和表面长波净辐射的估计。这项工作的目的是量化辐射方向性的影响。首先，使用三种类型的发射率数据来计算半球形发射率以及定向宽带发射率和半球形宽带发射率之间的差。发射率方向性非常重要，并且方向发射率随视角的增加而降低。可以发现在45 $ ^ {circ} $ –60 $ ^ {circ} $之内的视角，其方向发射率与半球形发射率非常接近，并且计算出的方向性和半球形宽带发射率之差为零。然后通过广泛的模拟确定表面温度下大气向下辐射与黑体辐射之间的差异。最后，给出了表面长波净辐射的误差范围。如果传感器的扫描角在$ pm 55 ^ {circ} $以内，则水和裸冰的误差分别高达17.48和14.05 $ hbox {W / m} ^ {2} $。对于半径不同的雪，误差小于2.74 $ hbox {W / m} ^ {2} $；地壳的错误可能达到4.11 $ hbox {W / m} ^ {2} $；对于矿物，沙子，煤泥和砾石，误差小于5.14 $ hbox {W / m} ^ {2} $；而clay的误差最小，为1.02 $ hbox {-/ m} ^ {2} $。

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