Utilisation of fluctuations in the intensity of reflected light to discriminate amongst different road surfaces

The most significant development in modern braking is the Anti-lock Braking System (ABS) The intervention of ABS, however, is not always advantageous. Major limitations arise when ABS is applied on loose unsealed surfaces such as gravel and sand. In the event of wheel 'lock up' on unsealed surfaces, the loose material forms a wedge in front of the tyre which contributes an additional braking force and results in shorter stopping distances. This paper considers the problem of distinguishing amongst various types of road surface by means of the Power Spectral Density (PSD) of fluctuations in the spectra of the intensity of laser light reflected from the road surface. To measure these fluctuations, a test rig was constructed consisting of a visible light laser diode coupled with a light-to-voltage sensor. By mounting the sensor at a height comparable to a vehicle under body and passing it over simulated road surfaces, it is possible to generate power spectral density charts for specific surfaces. It was discovered that each of the road surfaces tested had characteristic power spectral density charts, which could be used to discriminate between surfaces.