224 
From the data of figure 1, we have traced corresponding signatures 
(figure 2), reminding that the spectral response of the object corresponds 
at the representative curve of the reflected energy by this object, in the 
different wavelengths and particularly which correspond at channels of the 
satellites sensors. 
The obtained curves from the previous values do not reflect the variety 
of the established themes in the color composite image. In fact, several 
spectral responses of pixels of different colors converge to the same spectral 
signature which regroups, in this way, several themes. 
However, thanks to a coior palette carried out on the fifth channel, the 
one which distinguishes the best the previous curves, we could realize an 
approched map and the repartition of the main existing themes of the studied 
region (image 2). 
Image 2 
The limits of this adopted method for an identification of themes are 
essentially due to a discrete aspect of the realized curves, according to a 
spectral bands of the Landsat TM satellite (6 bands), which do not allow to 
represent variations of the continious curves corresponding to the real 
reflectances of the objects existing on the ground. 
DIFFRACTOMETRIC ANALYSIS 
The principle of the diffractometric analysis is as follows: 
One crystal is a diffraction network with three dimensions in which the X 
rays (electromagnetic waves) are diffused by the atoms electrons(fiojre 5)- 
During the 
the parallel j 
rays is produc 
2 d 
m : inte 
The X ray 
of crystals i 
crystalline an 
Therefore 
propose to mal 
by one diffrac 
caracteristic 
Laghouat (Algs 
more or less 
the differenci 
figure 4 and 
legend.