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 (RADF) as a function the phase angle ( α ), the photometric latitude ( φ ) and the photometric longitude ( λ ).
RADF = I F = π A M μ 0 k μ k − 1 where A M is the Minnaert albedo, k is an empirical parameter, I is the scattered radiance in the direction ( α , φ , λ ) , π F is the incident radiance, and
μ 0 = cos φ cos ( α − λ ) ; μ = cos φ cos λ . 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 k , 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.
