The Angular Transmittance Properties of Clouds

Richard T. Hall The Aerospace Corporation, El Segundo, Calif. 90245

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R. Douglas Rawcliffe The Aerospace Corporation, El Segundo, Calif. 90245

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Abstract

A series of experimental measurements of the visible light angular transmittance profiles of clouds is described. The results for single-layer overcast clouds were found to correlate well with standard hemispheric and narrow-angle pyrheliometric transmittances. The resulting expression for the angular transmittance profile of an overcast cloud layer is

              T(θ) = A+B sin2θ,

where

           A = −0.0056+0.89Tn , and B = −0.028+1.09Tw,

and T is the transmittance measured for a field of view at the detector subtending a half angle θ centered about the sun or other light source, Tn the transmittance measured with a narrow-angle pyrheliometer, and Tw the transmittance measured with a hemispheric pyrheliometer.

Abstract

A series of experimental measurements of the visible light angular transmittance profiles of clouds is described. The results for single-layer overcast clouds were found to correlate well with standard hemispheric and narrow-angle pyrheliometric transmittances. The resulting expression for the angular transmittance profile of an overcast cloud layer is

              T(θ) = A+B sin2θ,

where

           A = −0.0056+0.89Tn , and B = −0.028+1.09Tw,

and T is the transmittance measured for a field of view at the detector subtending a half angle θ centered about the sun or other light source, Tn the transmittance measured with a narrow-angle pyrheliometer, and Tw the transmittance measured with a hemispheric pyrheliometer.

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