- 589 - 
gives 
he dif- 
cident 
n of a 
The print-out describes with a proper symbol the situation: 
i-v 
ic techniques 
giving in this manner a first, rough thematic map. 
Note that by applying the ratio technique the images are 
normalized", that is their spectral information does not 
depend on the reflectance angle. 
the pho- 
licer. 
s. 
imina- 
ion and 
video 
ure and 
stem) . 
Thermal I.R. : electronic processes 
a) Slicing. 
It is performed by introducing a cluster of triergers 
between the tape recorder and the film printer. The trig 
gers are disposed in such a manner that the number of trig 
gers activated increases with the amplitude of the analogue 
signal coming in. The current at the triggers output is 
summed in a common resistor where the voltage steps are avai 
lable for an increasing applied input. Usually the human 
eye can distinguish 6-8 grey tones. For this reason our 
stage 
tion of 
ng one 
holding 
g to 
to three 
sign of 
olours 
y increa- 
little 
y out the 
hie pro- 
and red 
ame width). 
nown 
the three 
before: 
slicer configuration furnishes only 6 levels together. 
b) Sum, subtraction. 
A suitable electronic device based on operational am 
plifiers is used to sum algebraically two different signals. 
c) Derivation, integration. 
These operations are performed by a variable capacitor- 
resistor network. In this way it is possible to fit the 
R and C values to the frequency which is related to the 
texture of the targets. A full-wave rectifier provides 
the absolute value of the derivative function; this last o- 
peration is very interesting because of the fact that the 
thermal gradients are represented independently from the 
sweeping direction. 
d) Ratio, product, square root and power. 
These operations are accomplished analogically by using 
systems like Gilbert cell or a logarithmic and antilog array. 
Thermal I.R. : photographic processes 
. false 
n A/D unit, 
ions of 
a) Additive synthesis. 
As in the case of the multispectral techniaue, the 
I.R. bands can be composed by using different colours. 
We obtain in this way a special performance in which the in 
tensity is related to the absolute temperature T, while the 
resulting hue depends on the relative emissivity.