卷云对8 - 13微米红外天空辐射率的影响。 - Suppr

Appl Opt. 1968 May 1;7(5):891-8. doi: 10.1364/AO.7.000891.

An experimental investigation of ir sky radiance and radiance fluctuations in the 8-13-micro atmospheric window is reported. Measurements were made with ground-based, filtered bolometer detector radiometers under clear sky and cirrus overcast conditions. Sky radiance was measured very close to the limb of the sun to permit detection of the solar aureole caused by forward scattering by cirrus ice crystals. Polarized sky radiance was found at large zenith angles and is attributed to scattering by cirrus of thermal emission from the earth. The radiance due to tropospheric water vapor is predicted by means of a radiation chart. Measurements of clear sky radiance exceeded that predicted by the chart in all but one case. The radiance of visible cirrus greatly exceeds the radiation chart prediction. Diffraction about cirrus cloud particles leads to a prediction of a solar aureole of a size that corresponds to the measured aureole. It is concluded that even a cirrus haze, which is quite difficult for an unaided, observer to detect, can cause an excess zenith radiance of 0.1 mW cm(-2)sr(-1), which increases to twice this value at a zenith angle of 60 degrees . Even thin but visible cirrus clouds can easily produce an excess zenith radiance of 1 mW cm(-2)sr(-1), which increases by a factor 1.4 at a zenith angle of 60 degrees .

本文报道了对8 - 13微米大气窗口红外天空辐射率及辐射率波动的实验研究。测量是在晴空和卷云覆盖条件下，使用地基滤光测辐射热计探测器辐射计进行的。在非常靠近太阳边缘处测量天空辐射率，以便检测由卷云冰晶前向散射引起的日晕。在大天顶角处发现了偏振天空辐射率，这归因于卷云对地球热辐射的散射。利用辐射图表预测对流层水汽产生的辐射率。除一种情况外，晴空辐射率的测量值均超过了图表预测值。可见卷云的辐射率大大超过辐射图表的预测值。卷云粒子的衍射导致预测出一个与实测日晕大小相符的日晕。得出的结论是，即使是 unaided（此处原文有误，可能是 unaided，意为 unaided observer 即 unaided observer，指肉眼）观察者很难察觉到的卷云薄雾，也会导致天顶辐射率过量0.1毫瓦·厘米⁻²·球面度⁻¹，在天顶角为60度时增至该值的两倍。即使是薄但可见的卷云，也很容易产生1毫瓦·厘米⁻²·球面度⁻¹的天顶辐射率过量，在天顶角为60度时增加1.4倍。