Road Weather Management Program
photos of lightning, trucks plowing snow, an empty road before a storm, and an evacuation
Office of Operations 21st century operations using 21st century technologies

Best Practices for Road Weather Management Version 2.0

Best Practices > Publications > Publication Titles

Title:

Extended Photometric Model of Fog Effects on Road Vision

Abstract:

The road environment casts a luminance distribution into the eyes of the driver. In the presence of fog, the resulting visual signal is disturbed due to light scattering by airborne water droplets. This phenomenon has three major effects which cause an overall visibility loss: attenuation, halo and veiling. Koschmieder's law is widely used to describe how fog modifies the visual signal, but it only applies when observing non-luminous objects in daytime. In night-time and/or with self-luminous objects, luminance from scattered light can no longer be neglected. In this paper, the optical mechanisms underlying the visual effects of fog are first analyzed. Koschmieder's law is then extended in order to account for halos and back-scattered veil in the disturbed visual signal. The utility and validity of the resulting photometric model are discussed, and an example is provided which illustrates how it can be used to predict the image of a foggy road environment as seen by a driver. Despite its complexity, the presented model should find many applications, such as driving simulation or aiding device design.

Source(s):

16th Biennial Symposium on Visibility and Simulation

https://trid.trb.org/view/705149

Date: 2002

Author:

Dumont

Keywords:


Visibility
Forecast/Prediction

PDF files can be viewed with the Acrobat® Reader®.
Office of Operations