Optical Sensor for the Moisture of Pavement Surface Using the Reflection Flux Polarized

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  • 反射の偏光特性を利用する車両搭載用路面湿潤状態検出センサ
  • ハンシャ ノ ヘンコウ トクセイ オ リヨウスル シャリョウ トウサイヨウ ロ

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This paper is concerned with the development of a vehicle-borne optical sensor, which is useful for recognition of the moisture of various pavement surfaces as one of the parameters for vehicular antiskid control. The principle of this sensor is based on an increase in degree of polarization of the light flux reflected from the surface with an increase of its wetness.<BR>The light flux reflected from a specular surface, e. g. completely wet surface, is horizontally polarized well, when the incident angle is the Brewster's one; whereas, the light flux reflected from a diffuse surface, e. g. completely dry surface, is almost unpolarized. By making a measurement of the degree of polarization of the reflected flux, we can completely discriminate between the dry-and wet-surfaces, when the success probability of the classification is perfect.<BR>The increase in degree of polarization among the change from the dry-to wet-status results from the increase of the part of the specular reflection area occupied in the optical field-of-view to be tested.<BR>The degree of polarization of both the frozen and snow-covered surfaces (in Hokkaido area) was slightly smaller than that of the dry surface; so that, both of them should seem to be diffuse surfaces. It is difficult, therefore, to distinguish the frozen and snow-covered surfaces against the dry one with the classification probability of more than 90%.

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