Estimation of visibility using a visual image.

Optical-based visibility measurement instruments have been widely used to quantify atmospheric light extinction for decades. The light extinction coefficient is converted to visual range using a well-known formula since visibility is defined as the longest distance at which a black object can be observed against the horizon. In this study, a camera-based visibility monitoring technique was introduced to directly estimate visual range using a visual image obtained from a camera system. It was denoted as image visual range. The visual, optical, and geographical visibility monitoring were conducted to investigate the relationship between image visual range and distance from camera installed at the monitoring site. The visibility estimation formula, which is the function of the y position of the coordinates in the visual image, was introduced. And image visual range was estimated from the visual image using the chromatic analysis. It was found that the relationship between the image visual range and the y position of the visual image was a nonlinear function. The average relative error of image visual range less than 50 km was acceptable from the results of the relationship between optical-based visual range and image visual range. It was estimated that the relative error between two variables was not only attributed to the perspective and the faint outline of the visual image in the chromatic analysis but also associated with the assumption of the uniform distribution of the light extinction by aerosol within the field of view in the optical monitoring.