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Comment on “Persistence and Recurrence Probabilities of Cloud-Free and Cloudy Lines of Sight through the Atmosphere”

Charles L. MedlerTASC,Reading, Massachusetts

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Kenneth B. MacNicholTASC,Reading, Massachusetts

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Abstract

Although published some time ago, the subject paper represents a well-known resource for modeling and assessing cloud impacts on land-based and air-based electro-optical systems. The Lund dataset, derived from whole-sky photographs taken during the summer months at Columbia, Missouri, remains unique and valuable and has been used in assembling critical cloud-free line-of-sight models. In Lund's paper, cloud-free and cloudy persistence and recurrence probabilities, plotted versus elapsed time interval for each of 11 categories of fractional sky cover, are provided. The purpose of this comment is to provide an expression that properly combines these probabilities to produce persistence and recurrence probabilities irrespective of sky cover category (i.e., probabilities that are valid when the sky cover is not known a priori). Lund presented a “matrix model” for representing these probabilities. Lund's matrix model does not represent the average recurrence or persistence probability over all sky cover conditions, as is shown in the Appendix.

Abstract

Although published some time ago, the subject paper represents a well-known resource for modeling and assessing cloud impacts on land-based and air-based electro-optical systems. The Lund dataset, derived from whole-sky photographs taken during the summer months at Columbia, Missouri, remains unique and valuable and has been used in assembling critical cloud-free line-of-sight models. In Lund's paper, cloud-free and cloudy persistence and recurrence probabilities, plotted versus elapsed time interval for each of 11 categories of fractional sky cover, are provided. The purpose of this comment is to provide an expression that properly combines these probabilities to produce persistence and recurrence probabilities irrespective of sky cover category (i.e., probabilities that are valid when the sky cover is not known a priori). Lund presented a “matrix model” for representing these probabilities. Lund's matrix model does not represent the average recurrence or persistence probability over all sky cover conditions, as is shown in the Appendix.

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