An Automatic Visibility Measurement System Based on Video Cameras

Abstract

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