CARACTERIZATION OF ZONE OF STUDY 
Within this study, the data set used corresponds at a Landsat TM scene 
196/37 acquired the first of January 1989. 
The selected zone is considered as a transition zone between mountainous 
reliefs of the saharian Atlas and the plains of the beginning of the Sahara. 
This fringe, caracterized by a semi-arid and arid environment, cones of 
dejection at the outlets of rivers descended from the mountains, as well as 
the glacis elaborated by streamings, is favourable for human occupation which 
finds the necessary water for a life and lands for agricultural and pastoral 
activities. However, this kind of environment is also a fragile field submited 
at the agression of several dynamics, particularly the hydric and eolian 
ones, susceptible to disturb seriously the human activities. The man, also, 
contributes at the degradation of the environment by overgrazing, ill 
arrangements or inadapted techniques to the environment conditions. 
SPECTRAL ANALYSIS 
The aim of this analysis is to caracterize different themes existing in 
the studied region, for this objective, we have begin by a preselection of 
three channels among the TM channels in order to carry out a color composite 
imagery. The three selected channels are the TM4, TM5 and the TM6 averaged, 
the dynamics of channels have been judiciously chosen for a better 
exploitation of data into consideration of the resolution of channels TM4,TM5 
(30m) and thermic TM6 (120m). 
The resultant image presents the different themes discriminated by 
their colors ( image 1) 
Image 1 
The following table (figure 1) regroups reflectances , in selected 
points of ohe six channels of Landsat TM, with the different colored shades.