Cloud-Free Line-of-Sight Calculations

R. R. Rapp The Rand Corporation, Santa Monica, Calif. 90406

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C. Schutz The Rand Corporation, Santa Monica, Calif. 90406

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E. Rodriguez The Rand Corporation, Santa Monica, Calif. 90406

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Abstract

A method for computing the probability of a cloud-free line-of-sight (CFLOS) between a given point in the atmosphere and a given point on the earth, was developed. The method is based on 3-hr synoptic weather reports of clouds, and whole-sky photographs taken during daylight hours over a period of three years at Columbia, Mo. The computational procedure is an effort to eliminate an apparent oversimplification in previously published methods that results from the use of mean cloud cover, an unsatisfactory vertical cloud distribution, and sunshine data. Present results are at variance with those earlier estimates, but compatible with recent observations actually taken from aircraft. Although the CFLOS estimates obtained are, by nature, uncertain, the range of uncertainty was estimated by using published empirical data and a quantitative error analysis.

Abstract

A method for computing the probability of a cloud-free line-of-sight (CFLOS) between a given point in the atmosphere and a given point on the earth, was developed. The method is based on 3-hr synoptic weather reports of clouds, and whole-sky photographs taken during daylight hours over a period of three years at Columbia, Mo. The computational procedure is an effort to eliminate an apparent oversimplification in previously published methods that results from the use of mean cloud cover, an unsatisfactory vertical cloud distribution, and sunshine data. Present results are at variance with those earlier estimates, but compatible with recent observations actually taken from aircraft. Although the CFLOS estimates obtained are, by nature, uncertain, the range of uncertainty was estimated by using published empirical data and a quantitative error analysis.

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