Hernández-Andrés J, Romero J, Lee R L
Departamento de Optica, Facultad de Ciencias, Universidad de Granada, Spain.
J Opt Soc Am A Opt Image Sci Vis. 2001 Feb;18(2):412-20. doi: 10.1364/josaa.18.000412.
As part of our ongoing research into the clear daytime sky's visible structure, we analyze over 1,500 skylight spectra measured during a seven-month period in Granada, Spain. We use spectral radiances measured within 3 degrees fields of view (FOV's) to define colorimetric characteristics along four sky meridians: the solar meridian and three meridians at azimuths of 45 degrees, 90 degrees, and 315 degrees relative to it. The resulting clear-sky chromaticities in 44 different view directions (1) are close to but do not coincide with the CIE daylight locus, (2) form V-shaped meridional chromaticity curves along it (as expected from theory), and (3) have correlated color temperatures (CCT's) ranging from 3,800 K to infinity K. We also routinely observe that sky color and luminance are asymmetric about the solar meridian, usually perceptibly so. A principal-components analysis shows that three vectors are required for accurate clear-sky colorimetry, whereas six are needed for spectral analyses.
作为我们对晴朗白天天空可见结构持续研究的一部分，我们分析了在西班牙格拉纳达七个月期间测量的1500多个天光光谱。我们使用在3度视场（FOV）内测量的光谱辐亮度来定义沿四个天空子午线的比色特性：太阳子午线以及相对于它在方位角为45度、90度和315度的三条子午线。在44个不同视角下得到的晴空色度：（1）接近但不与CIE日光轨迹重合；（2）沿其形成V形子午线色度曲线（如理论所预期）；（3）相关色温（CCT）范围从3800K到无穷大K。我们还经常观察到天空颜色和亮度关于太阳子午线不对称，通常这种不对称很明显。主成分分析表明，精确的晴空比色法需要三个向量，而光谱分析需要六个向量。
