590 - 
In fact in this case we have a vectorial composition: the 
module of the vector represents the temperature value 
and its position the hue, that is, the relationship between 
the emissivity in band A and B ( see Figs. 3, 6). 
b) Density slicing of difference and ratio. 
The image obtained from the analogue computer and 
printing unit consists of a series of transparent points in 
an opaque field. By overlapping chosen couples of isoden 
sities corresponding to difference and ratio of channels 
A ( 3-5 micron ) and B ( 8-14 micron ) we obtain the system: 
A - E = Kl ; -I- = K. 
where Ki and Kj represent the position on the grey scale 
of the density J level, with a chosen and fixed amplitude. 
By dividing, as an example, the information given by A - B 
in 10 levels and applying the same procedure for the ratio 
we can consider 10 different combinations, that is, 100 
different target categories can be identified ( Fig. 4). 
This result is achieved by the use of an hybrid system. 
With the electronics the difference and the ratio are per 
formed while with the optics we obtain the solution of the 
system seen above. The exposed system offers the opportuni 
ty of a fast choise of the more meaningful levels for each 
particular purpose of study. 
MEANING OF SOME USED OPERATIONS IN THERMAL I.R.DATA ANALYSIS 
In the thermal I.R. there are two different branches, 
the energetic one studying the radiating power and its ex 
change with the environment and a second one involving the 
pattern recognition. The slicing in radiance levels, the 
drawing of the thermal gradients ( derivative function of the 
radiance) and their performance in isolevels as well as the 
gradient module represent the energetic point of view. 
Algebric sum and ratio are referred to the surface physical 
aspect of the bodies investigated. Compositions of functions 
like the following have a particular meaning for the inter 
preter : 
1) derivate A - integrative B (Fig. 8 ) the thermal textures 
of the investigated surface, emphasized by the derivation are 
related to the averaged value of the environment in order to 
enhance the microclimatic effect due to the vegetative zoning. 
2) Absolute value of the derivate function.( Fig. 9). 
This operation applied to the signal coming from an I.R. chan 
nel gives us a description of the surficial gradients distribu