Quantitative Calibration of Three-Wavelength Road-Condition Sensor Using a Dual-Wavelength Response Ratio

Assessing the condition of a road exposed to the atmosphere is crucial for safety. A three-wavelength road-condition sensor is a noncontact sensor that can be used for qualitative recognition and quantitative measurement of road conditions. However, the sensor is not robust to anomalous changes in the light intensity received that can be caused by several factors (such as changes in distance to the measuring point from a road bump or pothole). These changes cause the measurement state to deviate from the calibration state, reducing the sensor detection accuracy. However, existing studies on reducing the influence of the abovementioned problems on road-condition detection have only focused on how to ensure robustness in the qualitative classification of road-covering types, and no studies have been performed on how to ensure robustness in the quantitative measurement of the road-covering thickness. Thus, a quantitative calibration method for three-wavelength road-condition sensors using a dual-wavelength response ratio is proposed in this study. This method consists of using the response voltage ratio of two wavelengths to replace the response voltage of one wavelength during the quantitative calibration of sensors, making quantitative measurement insensitive to the deviation between measurement and calibration states. Comparison experiments were performed using the three-wavelength road-condition sensor calibrated by different quantitative methods, and an analysis was performed on the influence of the deviation of the measurement state from the calibration state on the quantitative measurement results and the measured covering thickness under changes in the measurement state. The experimental results verified the effectiveness of the novel approach compared with the traditional quantitative calibration method.