Concepts, terminology, and symbols are presented for specifying and relating directional variations in reflectance and emissivity of an opaque surface element. Their relationship to more familiar concepts, including those of perfectly diffuse and specular reflectance, is given, and they are applied to illustrative examples. It is shown that, when the usual reciprocity relationship holds, the reflectance for a ray incident on an opaque surface element is related by Kirchhoff's law to the emissivity of that element for a ray emitted along the same line in the opposite sense.
© 1965 Optical Society of America
Original Manuscript: May 11, 1964
Published: July 1, 1965
Fred E. Nicodemus, "Directional Reflectance and Emissivity of an Opaque Surface," Appl. Opt. 4, 767-775 (1965)