Full text: Remote sensing for resources development and environmental management (Volume 2)

687 
Data concerning Gl and G2 sub-frames are estimated 
and extrapolated since no drill has ever been tried. 
The top of the reservoir is rather shallow at site 
LG which can be referenced as surely affected by ge 
othermal influence. The following cross section, a- 
fter Calore et al. (1979), illustrates the geothermal 
situation schematically. 
Green and Red which correspond to the reflected e- 
nergy Green, Red and Infrared. 
Moreover, since the object of our investigation is 
to outline fine anomalies within visually homogeneous 
vegetated zones, we also have applied to the band 
ratios IR/Red, IR/Green and the so called Normalized 
Difference Vegetation Index (NDVl) where: 
. Impervious 
' complex 
Main aquifer 
Basal complex 
-1500 —* t 
Jtfm 
J Statute mile 
NDVI = — 
IR + Red 
On the basis of frequency distribution of DN present 
in the NDVI image and in agreement with the actual 
values of NDVI, we have operated a suitable level 
slicing as coded as follows. 
Table 4. Correlation between DN intervals and actual 
values of NDVI represented on the image. 
DN intervals Grey Level Code NDVI Values 
Figure 3. Geothermal cross section of the Travale 
field. Arrow outlines location of the sub-frames Gl, 
G2 and MA. 
The top of the reservoir dips north-eastward, benea 
th the cover of an impervious complex. The sub-frames 
G1,G2 and MA are sited in correspondance of a tecto 
nic feature -the graben of Travale- where associated 
fractures are the easy vehicle of the geothermal fl 
uid. This structural remark confirms the geothermal 
potentiality of the suspected zones. 
3 DIGITAL ANALYSIS OF THE I.R. AERIAL PHOTOGRAPHS 
The investigation has continued on the basis of spe 
ctral signature of vegetation, analysed on the IR 
False Colour stereo pairs. 
3.1 Image processing 
In order to avoid faults due to aberration of the 
camera lenses used and to the film developing pro 
cesses we selected the frames so that each test area 
occupies the central portion of them. Frames no. 035, 
077 and 101 resulted to be in good agreement with 
the requirements. 
The 4 sub-frames previously identified were scan 
ned, at a 100 pm resolution, and digitized by means 
of a drum microdensitometer Optronics 0-4500, 
Table 3. Dimensions of the windows digitized from 
the original transparencies. 
Site 
Frame no. 
Dimensions 
(no. pixels) 
Area 
(ha) 
Gl 
077 
212 X 173 
5.7 
G2 
077 
188 X 164 
4.8 
LG 
035 
119 X 137 
2.5 
MA 
101 
98 X 135 
2.0 
* 1 pixel = 1.25 m x 1.25 m 
Each window was scanned under separate reading of 
the 3 colour components of the film layers Blue, 
0 - 
- 126 
0 
< 
0. 
.0 
127 - 
- l4l 
30 
0.00 
- 
0.l4 
142 - 
- 156 
70 
0.15 
- 
0.29 
157 - 
- 171 
110 
0.30 
- 
0.44 
172 - 
- 186 
150 
0.45 
- 
0.59 
187 - 
- 201 
190 
0.60 
- 
0.74 
202 - 
- 216 
230 
0.75 
- 
0.89 
217 - 
- 255 
255 
> 
0. 
.9 
The band ratios IR/Red and IR/Green correlate the 
highest values of reflectance to the lowest and to 
the Green peak of vegetation, respectively. 
NDVI enhances the different stages of the vegetation 
vigour. 
The additive view of the 3 ratios also has been 
attempted by different coding for visual interpre 
tation. The most useful colour combination has 
resulted: IR/Red —> Blue, Green/IR -> Green and IR 
-> Red. 
The results obtained by the digitization of IR 
component and their elaborations have been imaged 
in a plate (see fig. 4). 
3.2 Output analysis 
Data deriving from the image processing have been 
represented under the form of images and statisti 
cal parameters. 
Since the sub-frames correspond to small and well 
confined areas, the statistical approach has seemed 
to be useful and more suitable than others. 
■f. In particular, the arithmetic mean m, the standard 
deviation a and the coefficient of skewness s have 
been considered. 
Values of standard deviations confirm that the 
sub-frame MA and Gl are the most uniform units. 
The values of a for IR/Green and NDVI images ap 
pear to be smaller than in the other cases. 
The skewness of ratios remains almost negative; 
that means the baricenters of the histograms are 
shifted to high DN of representation in relation to 
the primitive images. 
Mean values have been plotted and correlated.
	        
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