Lee Raymond L, Devan David E
Mathematics and Science Division, United States Naval Academy, Annapolis, Maryland 21402, USA.
Appl Opt. 2008 Dec 1;47(34):H116-27. doi: 10.1364/ao.47.00h116.
Beneath most overcasts, clouds' motions and rapidly changing optical depths complicate mapping their angular distributions of luminance L(v) and visible-wavelength radiance L. Fisheye images of overcast skies taken with a radiometer-calibrated digital camera provide a useful new approach to solving this problem. Maps calculated from time-averaged images of individual overcasts not only show their brightness distributions in unprecedented detail, but they also help solve a long-standing puzzle about where brightness maxima of overcasts are actually located. When combined with simulated radiance distributions from MODTRAN4, our measured radiances also let us estimate the gradients of cloud thickness observed in some overcasts.
在大多数阴天情况下，云层的运动以及迅速变化的光学厚度使得绘制其亮度L(v)的角分布和可见波长辐射率L变得复杂。用经过辐射计校准的数码相机拍摄的阴天天空的鱼眼图像为解决这个问题提供了一种有用的新方法。根据单个阴天的时间平均图像计算出的地图不仅以前所未有的细节显示了它们的亮度分布，而且还有助于解决一个长期存在的谜题，即阴天亮度最大值的实际位置。当与MODTRAN4模拟的辐射率分布相结合时，我们测量的辐射率还使我们能够估计在一些阴云中观测到的云厚度梯度。
