JPS576341A - Detecting method for freezing of road surface - Google Patents

Abstract

PURPOSE:To accurately detect a frozen state even in such a case when thawing materials are sprayed by making combined detection of the specular reflection outputs of visible light from road suefaces in a system of judging the frozen state when the temp. of the road surface is below a required temp. CONSTITUTION:A light projector 24, an irregular reflected light detector 25 for infrared light and visible light, a specular reflected light detector 26 for visible light and a thermometer 28 are mounted to a stanchion erected on a road. The signals from the photodetectors 25, 26 are sent to a logical circuit 44 and an arithmetic operating part 45, and the signal of the thermometer 28 is inputted to the part 45. By the signals thereof, the respective states of the road surface are judged. Even when the road surface is decided to be below a prescribed temp. and in a frozen state by the thermometer 28, snow melts from the snow cover of frozen state to water within a fixed time after spraying of thawing materials, and therefore the road surface temporarily changes into a specular state, and the output of the photodetector 26 for visible light increases. When this specular reflection output of visible light is in excess of a reference level, it is decided as a wet state and this is discriminated as the frozen state.