Degraded Visual Environments

doi:10.1117/3.2553485.ch6

Book: Photonics Rules of Thumb, Third Edition

Author(s): John Lester Miller, Katie Schwertz, Edward J. Friedman, John N. Sanders-Reed, Brian K. McComas

Published: 2020

https://doi.org/10.1117/3.2553485.ch6

Author Affiliations +

Abstract

Degraded visual environments (DVEs) are conditions under which normal human eyesight is reduced. This includes the presence of various obscurants such as rain, snow, fog, dust, smoke, haze, pollution, and so on. In the visible band (located in a region of the spectrum with very low atmospheric absorption), most degradation is due to multiple scattering of light from obscurant particles. This removes the correlation between the photon angle of arrival and the original scene content that originally emitted or reflected the photon resulting in a loss of contrast. The scattered photons are essentially just “noise” while the number of information-carrying photons rapidly decreases to nearly zero. The effect is best illustrated by heavy fog in which a light source (such as the Sun) may be difficult to locate. Instead of appearing as a crisp, bright disk against a blue sky, the Sun generates a diffuse glow that, if the fog is sufficiently heavy, appears to come from all directions. Gating an illumination source and its return can greatly reduce this problem.