and, if possible, the shadow which is very distinct on a false 
colour photograph. 
Consequently, stereovision is absolutely necessary to perform 
this process of convergence of evidence, which makes it pos- 
sible to rank the degree of damage. Four conditions are distin- 
guished and all damage indicators are expressed relatively to 
the image of the healthy trees. Table I gives an example. 
TABLE I : Relative damage indicators on colour infrared image 
and the four classes of the condition of the trees. 
  
  
CONDITION RELATIVE COLOUR CHANGES RELATIVE TEXTURE 
l. healthy "red" "normal" 
2. beginning less saturation of red, finer, less contrast 
leaf necrosis increasing brightness, 
and withering more pink hue, 
3. important well saturated colour, coarser, low con- 
damage becomes more yellow- trast 
brown, 
4. leafless and blue-green hue with im- fibrous branches 
dead, lethal portant transmission of visible. 
damage batkground reflection. 
  
5. The investigator is not interested in the detection and 
localization of the damaged trees only, but also tries to 
evaluate possible causes of the damage. For practical pur- 
poses these possible causes which can produce a relative 
colour change, are grouped into 7 classes : 
(1) biotic damage by insects... ; 
(2) physical soil deterioration as packing, uprooting, ground 
works ; 
(3) chemical soil pollution : leaks in gasconducts, salts in 
winter, pollution of the ground water ; 
(4) shortage of water and nutriciants ; 
(5) physical atmospheric deterioration : wind damage, overhea- 
ting of the crown in the summer ; 
    
  
  
  
  
  
  
  
   
    
   
     
    
      
   
    
   
  
  
   
    
     
    
   
  
   
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