Henyey–Greenstein phase function

A single-parameter analytic form for an anisotropic, scattering phase function. The Henyey–Greenstein phase function is written as

where θ is the scattering angle. The parameter g is conveniently equal to the asymmetry factor.
Henyey, L. G., and J. L. Greenstein 1941. Astrophys. J.. 93. p.70.