Accession Number : AD0763083

Title :   Joint Probabilities of Cloud-Free Lines-of-Sight through the Atmosphere at Grand Forks, Fargo, and Minot, North Dakota.

Descriptive Note : Air Force surveys in geophysics,

Corporate Author : AIR FORCE CAMBRIDGE RESEARCH LABS L G HANSCOM FIELD MASS

Personal Author(s) : Lund,Iver A.

Report Date : 23 MAR 1973

Pagination or Media Count : 25

Abstract : Signals transmitted through the atmosphere in the visible and infrared portions of the electromagnetic spectrum can be seriously degraded by clouds between the source and the receiver. A previously published model was developed for estimating probabilities of cloud-free lines-of-sight (CFLOS) through the atmosphere at any desired elevation angle and geographical location. This paper extends the published model to the problem of estimating probabilities of cloud-free lines-of-sight from n of m observing sites. A climatic record of sky cover observations taken simultaneously from all m sites is required before the model can be applied. The paper illustrates diurnal changes in CFLOS probabilities at Grand Forks of more than 0.15 and monthly changes of more than 0.30. It also illustrates that sky cover is not independent, even between Minot and Fargo which are 236 mi apart. Probabilities of CFLOS from at least one of the three sites, Grand Forks, Fargo and Minot, range from 0.59 during the worst month and hour to 0.93 during the best month and hour. (Author)

Descriptors :   (*ATMOSPHERE MODELS, *VISIBILITY), INFRARED RADIATION, CLOUD COVER, PROBABILITY

Subject Categories : Atmospheric Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE