Visibility

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visibility

[‚viz·ə′bil·əd·ē]
(meteorology)
In weather observing practice, the greatest distance in a given direction at which it is just possible to see and identify with the unaided eye, in the daytime, a prominent dark object against the sky at the horizon and, at nighttime, a known, preferably unfocused, moderately intense light source.

Visibility

 

the possibility of visual perception of objects that are distant from the observer. Visibility is characterized by degrees—that is, distinguishability (how clearly the object can be seen)—and by range—that is, the distance at which the object under observation is no longer discernible to the naked eye. Visibility is classified according to the observation medium as atmospheric visibility (in the air), underwater visibility (in water), and visibility in solid bodies (for example, in glass). Generally, an object’s distinguishability depends on its angular dimensions, the brightness level, the contrast between the background and the object, the time of observation, the degree of pollution of the medium, and other technical and physiological factors. The determination of an object’s visibility is one of the principal tasks of human engineering that is related to the development of automatic control systems, which include reflection devices for the visual and rapid transmission of information to the human operator.

REFERENCES

Inzhenerno-psikhologicheskie trebovaniia k sistemam upravleniia. Moscow, 1961.
Woodson, W., and D. Conover. Spravochnik po inzhenernoi psikhologii dlia inzhenerov i khudozhnikov-konstruktorov. Moscow, 1968. (Translated from English.)

V. P. ISAEV


Visibility

 

from an automobile, the extent to which an unobstructed view is provided of the area surrounding an automobile. Upward vision from the driver’s seat is determined by the limit of visibility for a point located 5 m above the road. Blowing warm air over the front windshield is an effective means of improving visibility for the driver in winter.

Rear visibility is determined by the size and location of the rear windshield; it can also be improved by the installation of additional rear-view mirrors and by heating the rear windshield in winter. Visibility is an important consideration in the design of vehicles and of machines used for hoisting and transportation.

M. B. AFANAS’EV

visibility

1. The quality or state of being perceivable by the eye.
2. The distance at which an object out-of-doors can be just perceived by the eye.
3. The size of a standard test object, observed under standardized viewing conditions, which has the same threshold as the given object.

visibility

The ability as determined by atmospheric conditions and expressed in units of distance, to see and identify prominent unlighted objects by day and prominent lighted objects by night (ICAO). The lighted objects are of specified candlepower. While measuring visibility, the nearest discernible object or light is taken into account.