In order to alert in advance car drivers to the danger of traffic accidents caused by the slipping of tires on frozen road surfaces, this report presents an identification method that can discriminate the frozen surface and wet one in high accuracy. Being different from the conventional methods of using information about wet condition and low temperature on the road, we propose another discrimination method that uses only quasi-millimeter waves. The report focuses on the phenomenological fact that the reflection of the waves from ice surface is greatly different from water one. For confirming such theoretical prediction, we carry out experiments in the laboratory using a portable and commercially available transmit/receive module with a 24GHz frequency band. The reflection coefficients are obtained by measuring standing wave ratios. Experimental data show that the reflection coefficients from the water film are stably greater than those from ice film on average. Thus obtained results demonstrate that the present method provides the feasibility of discriminating the water and ice surfaces on the road in actual environmental situation.
