Apparatus and method for measuring retroreflectivity of a surface

A method for measuring retroreflectivity of a road surface while moving across the road surface, the method comprising:

• providing an apparatus for measuring the retroreflectivity of the road surface while moving across the road surface, the apparatus comprising a light source for illuminating an area of said road surface at an incident angle relative to the road surface and a detector for detecting light reflected back from an observation area of the road surface at an observation angle relative to the surface;
• receiving a detector signal indicative of an intensity of light reflected back from the illuminated area of the road surface, and detected by the detector at the observation angle relative to the surface responsive to the illumination of the illuminated area at an incident angle relative to the road surface;
• determining, from at least the received detector signal, a measure of the retroreflectivity of the road surface;
• and
• receiving from at least one measurement device at least one measurement indicative of a distance between the apparatus and the illuminated area;
• wherein determining the measure of the retroreflectivity comprises adjusting the measure of the retroreflectivity responsive to the measured distance relative to a nominal distance.

An apparatus for measuring retroreflectivity of a road surface, the apparatus comprising:

• a light source for illuminating an area of said road surface at an incident angle relative to the surface;
• a detector for detecting light reflected back from an observation area of the road surface at an observation angle relative to the road surface;
• a signal processing unit adapted to receive a detector signal from the detector and to determine, from at least the received detector signal, a measure of the retroreflectivity of at least a part of the road surface;
• and
• at least one device for measuring a distance between the apparatus and the illuminated area,
• wherein the signal processing unit is further adapted to adjust the measure of the retroreflectivity responsive to the measured distance;
• wherein the observation angle is smaller than the incident angle.