The aerial photographs were taken previously(in 1975) 
and were especially useful as the zones being examined have 
undergone no change in the years since then, as far as these 
groups are concerned. 
Available data was supplied in positive black and white 
trasparencies in the four Landsat channels ((D)). These were 
enlarged electronically at a ratio of 6:1 (produced then about 
at 1:166,667) after the data had been expanded radiometrically 
so that the centre of the gray scale fell around the density 
corresponding to the average relative signature of the agri 
cultural species in t he zone at the mostjrigorous phenological 
stage prior to ripening | 
Radiometric expansion allowed signatures lying in the vicinity 
of average signatures of vigorous vegetation to be emphasised 
while the lowest signatures (bare ground,urban settlements and 
the like)and the higest ones (shores,snow and others) were 
"compressed". 
During the analysis of each of the available scenes the 
combination of channels 4 and 5 were inverted photographically, 
so that the non-agricultural coverages in these two channels 
had larger signatures than the vegetation ones; by inverting 
the process the non-agricultural signatures were "depressed" 
and the agricultural ones emphasised. The trasnsparencies of 
channels 6 and 7 were then superimposed over the inverted 
scene of channels 4 and 5 using a shot of the combination. 
As the relations between signatures in channels 6 and 7 
are inverted compared to the existing ones in channels 4 and 5 
a black and white map emerges which emphasises only the 
signatures around which radiometric expansion is centred: 
in this case the vigorous vegetation signatures. 
     
     
   
   
   
   
   
   
    
   
   
    
   
   
    
   
   
   
   
   
   
   
   
    
   
   
   
   
    
    
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