An Automatic Visibility Measurement System Based on Video Cameras

The Minnesota Department of Transportation (MnDOT) 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 nighttime, 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. MnDOT 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 nighttime evaluation very difficult. However, research verified that the trend of visibility change obtained by the proposed approach closely approximates the trend of manual measurements.