Help for PHOTFIT2_MINNAERT


PURPOSE:

In this PDF, the user is asked for the parameters and there limits needed to  
fit Minnaerts's photometric function. This function needs just two input 
parameters (Albedo, geometric exponent k) and there absolute limits.
If a sulution guess falls out-of-bonds then the attemp will be aborted and 
a new guess attempted.

MATHEMATICAL BACKGROUND :

It is found empirically that Minnaert's law approximately describes the 
variation of brightness of many surfaces over a limited range of angles.
But the general law breaks down completely at the limb of a planet.

Minnaert (1941) suggested generalizing Lambert's law so that the power emitted 
per unit solid angle per unit area of the surface be proportional 
(cos(i)*cos(e))**k [ Lambert's power is proportional to (cos(i)*cos(e))**1 ].

bidirectional reflectance [1/str] :

r(i,e,g)=ALBEDO*(cos(i)*cos(e))**EXPONENT/cos(e)

REFERENCE :
M. Minnaert, The reciprocity principle in Lunar photometry,
Astrophysical Journal, Vol. 93, No. 2, p. 403-410, 1941
PROGRAMMER:

Friedel Oschuetz
Institute of Planetary Exploration
DLR
12484 Berlin (FRG)