Directional reflectometer

Abstract

The present invention is a directional reflectometer that measures, for example, the optical bidirectional reflectance distribution function [BRDF] of a surface in situ on a finished article, e.g. a vehicle, to provide information on its surface reflectivity and emissivity. The light wavelength may be IR, near-IR, visible, UV, or longer wavelengths. Light, preferably focused to a small spot on the surface, is projected onto the surface at an angle adjustable in azimuth and elevation. A wide angle mirror, lens system, or both transfers light scattered from the surface onto an imaging sensor, preserving scattering angle information and thereby permitting the BRDFs for a given incidence angle and all scattering angles to be measured simultaneously. A computer reads the sensor outputs and analyzes the quality of the surface in a factory or field environment.

We claim:  
     
         1 . A method for measuring the reflectance of a surface, comprising the steps of: 
 (a) illuminating the surface with radiation focused at the lower focus of an ellipsoidal mirror to produce a reflection by scanning the incident radiation that illuminates the surface through angles between normal and grazing, up to about 88° from the normal;    (b) directing the reflection from the surface collected at the upper focus of the mirror to a detector, and    (c) analyzing the reflection in the detector to determine the reflectance.