Apparatus and method for determining precision reflectivity of highway signs and other reflective objects utilizing an optical range finder instrument

摘要

An apparatus and method for measuring coefficients of retroreflectance of retroreflective surfaces such as road signs involves use of a modified light based range finder. The apparatus includes a power attenuation factor data base which relates pulse width of received pulses to power attenuation of the transmitted pulses. The range finder calculates target range based on time of flight of light pulses. The apparatus automatically calculates the absolute coefficient of retroreflectance for an unknown reflective surface being measured by comparison of the measurement to a reading with the same instrument of a known reflectance standard. The method involves either recalling a stored standard reference reflectance factor or determining a reflectance factor via the range finder for a sample of retroreflective material with a predetermined coefficient of retroreflectance, and then measuring the distance to an unknown target, determining a power attenuation factor from the received pulse width from the unknown target and then calculating the absolute coefficient of retroreflectance based upon these determined values of power attenuation factor, distance and the reference reflectance factor.