HORIZONTAL VISUAL RANGE IN POLAR WHITEOUT.
MAIN UNIV (WEST GERMANY) METEOROLOGISCH-GEOPHYSIKALISCHES INSTITUT
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A theory on the horizontal visual range of objects of any color under overcast sky and over homogeneous ground is briefly outlined. The theory takes into account the influence of the visual ground albedo on the illumination of the object and the dependence of the contrast threshold of the human eye on the visual angle subtended by the object viewed. The object always appears darker than the horizon. The visual range of a black object is greater than that of any brighter object and is independent of the visual ground albedo. The visual range of objects of low or medium visual albedo is also almost independent of the visual ground albedo so that they may be considered as equivalent to black objects. But the visual range of white objects strongly depends on the visual ground albedo it tends to zero when the visual ground albedo is greater than 0.94 even in clear air. The effect of the visual angle and hence of the diameter of the object on its visual range becomes marked only for visual angles smaller than 0.2 degrees. The results explain the optical conditions encountered in polar whiteout. Measurements made in whiteouts in North Greenland proved the validity of the theory. Author
- Anatomy and Physiology
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