Polarization measurement of black ice with a Stokes polarization camera

Abstract

In cold regions, black ice is a condition in which the road surface appears to be only wet, but is frozen. When drivers notice black ice on the road, it is too late to apply emergency braking, and black ice has been the cause of traffic accidents and fatalities. Black ice is difficult to detect with the naked eye or a conventional imaging camera. In this study, a Stokes polarimeter, which can detect various polarization states, was used to compare the polarization components of wet and frozen road surfaces while changing the image angle. The results showed that there were various characteristics and differences in the Stokes images for both wet and frozen road surface conditions and for each imaging angle. The usefulness of the method was confirmed by using ROC curves to discriminate between frozen and wet road surfaces in the obtained Stokes images.