Daytime Visibility, A Conceptual Review,
Abstract
Daytime visibility is defined as the distance a black object can be seen against the horizon sky. Data on visual thresholds for daylight illumination are examined and the degradation of the contrast by the atmosphere described. The visibility as reported in meteorology correlates well with a contrast threshold of 0.05 and thus the attenuation coefficient and threshold sighting range product is equal to 3 alpha gamma equal to 3. Psychophysical data on visual thresholds for 0.33 second glimpse times when corrected to confident viewing with a 4 degree uncertainty of target position, predict the visibility distances well and indicate that the meteorological observers are using targets subtending on the average about 7.6 minutes of arc. Visibilities have an uncertainty of approximately + or - 20 percent in relation to measured physical parameters of air clarity. The errors in visibility distance inherent in the use of non-black targets and backgrounds other than the horizon sky are delineated. Some of the physical methods of measuring air clarity are described with reference to their use in obtaining a measure of visibility. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1979
- Accession Number
- ADA085451
Entities
People
- Jacqueline I. Gordon
Organizations
- Scripps Institution of Oceanography