The Volume Scattering Function, or VSF, notated mathematically as *ß *("beta"), is one of the two fundamental IOPs, and characterizes the intensity of scattering as a function of angle.

The VSF is defined in terms of a beam of light incident on an infinitesimal volume. At each angle from 0° (the original angle of the incident light) to 180°, the VSF is the ratio of the intensity of scattered light (in W/sr) to the incident irradiance (in W/m^{2}), per unit volume (in m^{3}). Therefore the VSF's units are (W/sr) / (W/m^{2} ? m^{3}) = sr^{-1} m^{-1}.

The total scattering coefficient *b* is calculated by integrating *ß* over all angles. The backscattering coefficient *b*_{b} is similarly derived by integrating over the angles from 90° to 180°.

Discussions of scattering often refer to the **Scattering Phase Function**, which is equal to *ß/b.* Because *b* is the integral of *ß *with respect to angle, the integral of the phase function with respect to angle is 1.