Bidirectional reflectance distribution function

A material's Bidirectional reflectance function, or BDRF, defines the ratio of light reflected from a surface to the incident luminosity. A function of phase angle $\alpha$, azimuth angle $\phi$, and angle of incidence i, BDRF models have been developed for various materials, and often contain additional parameters in addition to the primary angles. One such model, developed quasi-experimentally by astronomer Bruce Hapke at the University of Pittsburgh, introduces five such quantities:

• w - Single scattering Albedo

• h - Width of the opposition spike

• S(0) - Amplitude of the opposition spike

• g - Asymmetry Factor

• $\theta$ - Effective surface tilt

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References:

• Helfenstein, P., & Veverka, J. 1989 in Asteroids II, ed. R. P. Binzel, T. Gehrels, M. S. Matthews (Tucson: Univ. Arizona Press), 557

• Drake, J.S. 2004, A Photometric Study of Phocaea Group Asteroid 1584 Fuji, Senior Honors Thesis, Department of Physics and Astronomy, Dickinson College, Carlisle, PA