A dual beam bidirectional reflectance attachment, which permits the sample plane to be tilted to plus or minus 45°, is described. No restriction is placed on the type of sample which can be investigated because the incident light impinges on the sample from above. Reflectance spectra of a variety of materials are shown, as well as an indicatrix for a specular and a diffuse reflector. The use of this attachment provides spectra of the kind necessary for interpreting terrestrial and planetary remote sensing data.
Graham R. Hunt and Howard P. Ross, "A Bidirectional Reflectance Accessory for Spectroscopic Measurements," Appl. Opt. 6, 1687-1690 (1967)