Visibility Degradation On The Road
Adverse weather situations such as fog, mist, smoke, or haze present numerous challenges to drivers, including strong negative visual effects and decreasing the ability to see through the air. These challenges arise because of the luminance contrast reduction which is truly relevant to driving safety since factors like the absolute light level, the size of the objects to be seen, and the contrast between objects and their background are related to visual performance. A rapid decrease of the contrast of objects in the viewing field, the scattered light result not only in a complete loss of object detection but also recognizing those objects becomes tough and visual response time considerably increases. Moreover, due to the reductions in the optical fidelity of the aging eye older drivers will be most affected. Particularly in fog, the scattered light becomes more detrimental and small objects approach the visibility threshold. This, in turn, leads to fatal incidents in roads. To be more precise, according to the statistics provided by National Highway Traffic Safety Administration (NHTSA) of US that 28% of all crashes occurred in inconvenient weather conditions. Additionally, the World Health Organization (WHO) declared that one person is killed every 25 seconds because of road injuries. During perturbed atmospheric conditions, the estimated average of total annual accidents is around 31385 and over 511 road fatalities and almost 12,000 injuries in fog-related vehicle crash each year. Because of the dense fog with visibility of 50-60 meters in South Korea, a tragic accident caused deaths of 11 people and more than 50 serious injuries.
Furthermore, visibility degradation weather situations strongly decrease the image quality of a captured outdoor scene. Since visibility is much better in a clear weather condition than air polluted with an extensive amounts water droplets or dust particles in the atmosphere. The key reason for the degradation of outdoor image quality in foggy or misty conditions is large amounts of suspended fog or mist particles in the air which lead to the diffusion of most part the light prior to reaching the camera or another optical device. As a repercussion, blurring happens in the whole image. These kinds of degraded and poor visible image scenes considerably influence typically working computer vision algorithms and embedded systems which are massively used in many spheres. Say, for instance, water transportation, and aviation industry; navigation, tracking applications, and monitoring systems; outdoor recognition, detection, and segmentation; intelligent transportation systems; optical and camera-based applications which are used in the military and security agencies etc. The initial implementation for sensing weather situations using camera imagery was performed for the USA Army for supporting their ground operations on the battlefield. Researchers utilized digital cameras that deployed for military services to monitor enemy forces, to gather and analyze real-time weather data. However, at present, numerous safety and traffic monitoring cameras are deployed throughout the country and widely used for various vision-based applications. Most of these cameras videos and images are available on the internet and can be almost used real-time access. In facts, US acquires approximately 30 million surveillance cameras and 4 billion hours of footage per week. Moreover, in UK and South Korea, the estimated total number of installed closed-circuit television (CCTV) cameras is 5 million and 1 million, accordingly. Deployments of cameras still broaden in both the amount and complexness of camera imagery demand that automated algorithms be developed to be simply used operationally by users.
Visibility is considered as a meteorological variable and given various definitions in the Glossary of Meteorology. As stated by WMO and CIE, the visibility is defined as the longest distance at which a black object of suitable dimensions, located on or near the ground, can be seen and also recognized when observed against the horizon sky. Meteorological visibility is defined in terms of the transparency or transmittance of the atmosphere and it is accurately measured using forward scatter visibility sensors and transmissometers. Obviously, most of these sensors are too expensive and installation costs high. In addition to this, the sample volume of these devices is small so measurements are representative only for a small zone, though visibility can vary quite broadly on a small spatial scale.
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