The Minnesota Department of Transportation (Mn/DOT) conducted a two-year study on visibility measurement methods using
video cameras. This report describes the study's theoretical basis, practical methods, and experimental results.
Among several methods and algorithms developed, the edge decay model along with a proper threshold technique worked best
for evaluating daytime visibility. This approach estimates the distance where an object of specified size and shape is no longer
distinguishable from the background in terms of edge information. For night time, a constant light source is required to
evaluate visibility. Researchers developed a light diffusion model that follows an exponential decay curve.
Researchers determined that the volume of light diffused out of the original source logarithmically correlates to visibility.
Mn/DOT implemented day and night algorithms in the field and evaluated them using manual measurements. For daytime,
visibilities measured using the edge decay model closely approximated the manual measurements on all types of weather.
Unreliability of manual measurements at night made night-time evaluation very difficult. However, research verified that the
trend of visibility change obtained by the proposed approach closely approximates the trend of manual measurements.
Kwon, Taek Mu.
An Automatic Visibility Measurement System Based on Video Cameras.
Minnesota Department of Transportation.
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