Abstract

A theory is developed for the spectral irradiance of the overcast sky, and also of the top of the overcast, in terms of incident radiation, droplet size and concentration, and cloud thickness. The absorption of light by cloud water is allowed for.

Some samples of highly polluted cloud water have been spectrophotometered, and calculations made which show that the absorption produces very little effect in the visible spectrum, and only a moderate effect in the ultraviolet, even for very impure cloud water. On the other hand, the color of the ground has a considerable effect on the spectral irradiance of the overcast sky, and thus on its color. The color of the top of the overcast is, however, not greatly affected by that of the ground.

© 1954 Optical Society of America

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