Phase function

From Glossary of Meteorology

phase function

A function describing the dependence of scattered radiance on scattering angle.

The phase function is a dimensionless and normalized version of the scattering function, such that the integral of the phase function over 4π steradians equals 4π. The phase function for a given wavelength is a property of the medium, not of the incident radiation, provided the incident radiation is unpolarized. As the size parameter of a scatterer increases, its phase function becomes more anisotropic, with progressively more of the scattered radiance being concentrated into a diffraction peak.
See also Rayleigh phase function, Henyey–Greenstein phase function.