Instrumentation at the National Institue of Standards and Technology for bidirectional reflectance distribution function (BRDF) measurements

A description is given of the goniometric optical scatter instrumentation (GOSI) which has been developed at NIST for measuring the bidirectional reflectance distribution function (BRDF) from surfaces. The source, goniometer, and receiver are described. The systematic optical and electronic noise of the system is reported. The systematic electronic noise and background scatter have been reduced to allow a detection limit of 1 X 10-9 sr-1. This value is the Rayleigh scattering level from the air molecules in the room with a field of view of 7.2 cm at the sample position for 633 nm incident laser light.