Visibility

Use of the Visual Range of Detection to Estimate Effective Sweep Width for Land Search and Rescue Based On 10 Detection Experiments in North America

“…These factors include improved vigilance, general knowledge of location, and knowledge of size and general time of when a detection should take place. 30 More recently, research on the effects of being cued (alerted) on vigilance tasks similar to visual searching have been reported. 31 It can also be hypothesized that the unalerted searcher correction factor varies with contrast or visibility.…”

Visual range :

“…For more complete treatments see Middleton [95] and Duntley [32,33] and the references listed therein. Effects of ground/horizon sky luminance ratio and contrast on visibility factor for objects with a terrestrial background, based upon a contrast threshold of 0.05.…”

Electronic and Optically Generated Aircraft Displays: Study of Standardization Requirements

“…On the other hand, Gordon (in Duntley et at., 1964) cites two reports on clear weather sky conditions at sea level. These establish sky illuminance at approximately 10,000 foot-candles when the sun is at zenith.…”