Device for determining the state of roads

摘要

Fastened to a mast (2) positioned at the edge of the road surface (4) there is a bracket (3). A light projector (1) is fastened to the bracket in such a way that it projects infrared light under a constant incident angle onto a detection zone of the road surface (4). A reflected-light sensor (11) is fastened to the bracket (3) in such a way that it receives the light reflected at the road surface (4) at an angle which is equal to the incident angle. A scattered-light sensor (21) is fastened to the bracket (3) in a position different from that of the sensor (11) in such a way that it receives light diffusely reflected at the road surface (4). The sensors (11 and 21) contain photoelectric transducer elements and infrared filters which are arranged in front of the former. The filters pass infrared radiation only, so that external light originating from the sun or the road lighting system is reduced. The photoelectric transducer elements generate output signals which represent the radiation energies in the directly and the diffusely reflected light. A signal processing unit (5) contains amplifiers, multipliers, low-pass filters, comparators and a decision circuit which on the basis of the signals obtained judges the state of the road to be "dry", "wet", "snow-covered" or "frozen".