A method and an apparatus for determining the covering on a road surface. A measurement signal is fed into a pair of electrodes inlaid in the road surface and acting as a detector (5), whereby the ratio of the measurement current to the voltage formed across the detector (5) is determined in order to...http://www.google.com.tw/patents/US4745803?utm_source=gb-gplus-share專利 US4745803 - Method and apparatus for determining the covering on a road surface
