Denso has developed rain-proof technology for white line recognition sensors for use in vehicle control systems with 4m-distance platooning, and presented the technology at the 30th Japan Symposium on "Sensors, Micromachines and Applied Systems" (held in Sendai, Miyagi Prefecture, Japan from November 5 to 7, 2013, hosted by the Sensors and Micromachines Division of the Japan Institute of Electrical Engineering) (speech number: 5PM1-B-5).

       Denso is currently developing platooning technology for commercial vehicles such as trucks in the "Research and Development for Coordinated Driving (Automated Driving)" project, an energy ITS promotion business of the New Energy and Industrial Technology Development Organization (NEDO) of Japan (see this site report). If the distance between vehicles is kept at 4m and four vehicles are platooned at a speed of 80km/h, fuel consumption can be reduced by 15%. This is because the air resistance of the vehicle behind will be reduced.

LDIR is an infrared laser radar developed by Denso. The picture is taken from Denso's presentation

    The purpose of this research and development is to realize a vehicle control system without setting up equipment on the roadside, and to specify the position of the vehicle through white line recognition technology. In order to accurately recognize white lines, it is necessary to develop technology that can improve the recognition rate under conditions of poor visibility such as fog or rain.

       This time, Denso introduced an algorithm that can improve the recognition rate under rainy conditions. White line recognition uses infrared laser radar. The radar is installed from the top of the vehicle downward, and infrared laser is irradiated to the road surface to identify the white line through reflected light. When it rains, the road will be submerged in water, and it is difficult to distinguish the reflected light from the white line part and the part without white line (usually asphalt road surface). In addition, falling raindrops will also reflect the laser, and these reflected lights are also difficult to distinguish from the reflected light from the white line.

       Denso's test results show that if the depth of the road submerged in water is within 50mm, the white line can be accurately identified by properly setting the angle of the infrared laser radar. However, the influence of raindrops still exists at this time. Therefore, in order to remove the influence of raindrop reflected light, when it rains, the minimum value is selected from the past 6 data samples in the data of the reflected light waveform (regarded as data of non-raindrop reflected light), and the position of the white line is inferred based on the waveform synthesized by these minimum values. By the way, the selection of the minimum value from the past 6 data is determined by experiment. In this way, the difference in reflection intensity between the white line and the asphalt road surface can be made to the same level as on sunny days (>2dB).