Authors
F.E. Nicodemus, J.C. Richmond, J.J. Hsia, I.W. Ginsberg, T. Limperis
NATIONAL BUREAU OF STANDARDS
Portals
Summary
This paper formalized the bidirectional reflectance-distribution function (BRDF) and reflectance concepts as well as the basic set of reflectance nomenclature.
Abstract
A unified approach to the specification of reflectance, in terms of both incident- and reflected beam geometry, is presented. Nomenclature to facilitate this approach is proposed. Under specified conditions-including uniform irradiance, a uniform, isotropic, plane surface, and allowance for edge effects due to sub-surface scattering-the geometrical reflecting properties of a reflecting surface are readily characterized or specified in terms of the bidirectional reflectancedistribution function (BRDF). The BRDF is a derivative, a distribution function, relating the irradiance incident from one given direction to its contribution to the reflected radiance in another direction. Nomenclature (concepts, terms, symbols, and units) for categorizing and specifying reflectance quantities for a variety of different beam configurations (both incident and reflected beams) is described, and all are defined and interrelated in terms of the BRDF. The conditions under which the formalism can be applied, including situations involving considerable sub-surface scattering, are carefully established. The entire treatment is limited to the domain of classical geometrical-optics radiometry and does not take into account interference and diffraction phenomena, such as are frequently encountered with highly coherent radiant flux. The other radiation parameters such as wavelength, (temporal) modulation, and polarization and the effects of fluorescence (or phosphorescence) are discussed briefly.