ABSTRACT
This chapter argues that modern psychophysical theories provide the only hope of finding a scientifically sound, quantitative relationship between observed or calculated optical effects of pollution and perception. It examines one area with important application to visibility issues, the perception of transparency. The most important objects of visibility studies, plumes and haze layers, are often seen subjectively as layers with varying transparency. Only visual psychophysics can answer questions of perceptible thresholds in contrast or color, or can predict just-noticeable differences in scenic vistas caused by changes in optical properties of the atmosphere. A simple experiment was carried out that supports the analysis, using simultaneous observations of relative physical brightness and perceived brightness. Perceptual transparency effects have a significant effect on the appearance of regional and layered haze. The perceptual transparency index is, in effect, a subjective variable that controls the appearance of the mountain and haze.
