Minnaert function

The Minnaert function is a photometric function used to interpret astronomical observations and remote sensing data for the Earth. It was named after the astronomer Marcel Minnaert. This function expresses the radiance factor as a function the phase angle, the photometric latitude and the photometric longitude.
where is the Minnaert albedo, is an empirical parameter, is the scattered radiance in the direction, is the incident radiance, and
The phase angle is the angle between the light source and the observer with the object as the center.
The assumptions made are:

the surface is illuminated by a distant point source.
the surface is isotropic and flat.

Minnaert's contribution is the introduction of the parameter, having a value between 0 and 1, originally for a better interpretation of observations of the Moon. In remote sensing the use of this function is referred to as Minnaert topographic correction, a necessity when interpreting images of rough terrain.