Infrared-based determination of the type and condition of the road surface

The knowledge of different road conditions is a significant factor in determining their impact on fully automated driving. As part of the research project “SeeRoad” funded by the German Federal Ministry for Economic Affairs and Energy (BMWi), a system with various technological approaches is being developed, in order to estimate road conditions. One of these approaches determines the condition of road surfaces as well as the distance between the vehicle or sensor and the road surface, based on infrared (IR). In order to distinguish between a wet and a dry surface, the water film height (WFH) is measured by infrared rays. We present a procedure for determining the type and condition of the road surface with the help of infrared radiation, which forms a basis for the multiple sensor system. This procedure is tested in a laboratory setup that is suitable for reproducible measurements. A new approach to detect road surface wetness by using a combination of infrared sensors, which work with different principles, is presented. The first principle is based on the intensity measurement of a reflected IR signal to determine the distance. Here the intensity depends on the material surface. At a constant distance, different intensities are measured for the absorbed and reflected signal, depending on the color and texture of a material. In the second principle, the transit time of the emitted and reflected beam is measured, which is independent of the intensity. Thus, the combination of both methods allows the distance and type of road surface to be calculated.