Abstract

Digital images of overcast skies as seen from the earth’s surface open new windows onto the angular details of overcast colors and visible-wavelength spectra. After calibration with a spectroradiometer, a commercial CCD camera equipped with a fisheye lens can produce colorimetrically accurate all-sky maps of overcast spectra. Histograms and azimuthally averaged curves of the resulting chromaticities show consistent, but unexpected, patterns in time-averaged overcast colors. Although widely used models such as LOWTRAN7 and MODTRAN4 cannot explain these characteristic patterns, a simple semiempirical model based on the radiative transfer equation does, and it provides insights into the visible consequences of absorption and scattering both within and beneath overcasts.

© 2008 Optical Society of America

Colors of the daytime overcast sky

Raymond L. Lee and Javier Hernández-Andrés
Appl. Opt. 44(27) 5712-5722 (2005)

Observed brightness distributions in overcast skies

Raymond L. Lee, Jr., and David E. Devan
Appl. Opt. 47(34) H116-H127 (2008)

Tropospheric haze and colors of the clear daytime sky

Raymond L. Lee
Appl. Opt. 54(4) B232-B240 (2015)

The Color of the Overcast Sky

W. E. Knowles Middleton
J. Opt. Soc. Am. 44(10) 793-798 (1954)

Atmospheric ozone and colors of the Antarctic twilight sky

Raymond L. Lee, Jr., Wolfgang Meyer, and Götz Hoeppe
Appl. Opt. 50(28) F162-F171 (2011)