| 摘要 |
Light is projected upon a road surface (LD) from a road surface lighting light source (11). Diffusedly reflected light from the road surface (LD) are received by photodetectors (31A ad 31B) through a spatial filter, and the light reception signals are fed to a differential amplifier circuit (51). A tracking band-pass filter (52) extracts the center frequency component corresponding to the spatial frequency of a spatial filter, and an amplitude measuring circuit (54) measures the intensity (Da) of the component. A tracking low-pass filter (55) and an amplitude measuring circuit (56) measure the intensities (Db) of low-frequency components corresponding to spatial frequencies lower than that of the spatial filter. A judging circuit (60) judges whether the road surface (LD) is covered with snow, gravels, or asphalt. <IMAGE> |
