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On the determination of surface emissivity from Satellite observations

机译：通过卫星观测确定表面发射率

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摘要

Terrestrial brightness temperatures measured from satellites have been used to determine the surface emissivity. The results not only depend on surface temperature and on atmospheric properties, but also on the type of surface scattering. For otherwise identical conditions (same emissivity, same nonscattering atmosphere), the radiation above the Lambertian surface is larger than for a specular surface if the incidence angle is smaller than about 55/spl deg/. The opposite is true for larger angles. The effect leads to overestimates of emissivity for observations especially near nadir with the use of algorithms assuming specular reflection. The problem may be solved by the introduction of a specularity parameter to characterize realistic surfaces by a combination of specular and Lambert scattering. A simple solution lies in the use of conically scanning radiometers at a constant incidence angle near 55/spl deg/. Although the topic applies to all ranges of thermal radiation, the present discussion concentrates on the microwave spectrum in the Rayleigh-Jeans approximation.
机译：从卫星测得的地面亮度温度已用于确定表面发射率。结果不仅取决于表面温度和大气特性，还取决于表面散射的类型。对于其他相同的条件（相同的发射率，相同的非散射气氛），如果入射角小于大约55 / spl deg /，则朗伯表面上方的辐射大于镜面表面的辐射。对于较大的角度则相反。使用假定镜面反射的算法，该效果会导致高估发射率，尤其是在天底附近的观测。通过引入镜面反射参数以结合镜面反射和Lambert散射来表征真实表面，可以解决该问题。一个简单的解决方案在于以恒定入射角接近55 / spl deg /使用圆锥形扫描辐射计。尽管该主题适用于所有范围的热辐射，但本讨论着重于瑞利简斯近似中的微波频谱。

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