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4.2. Selection of training areas and location of training pixels 
Training areas for the establishment of the spectral signatures had to 
meet the following requirements: they had to be sufficiently large, easy 
to locate and their radiance had to be relatively homogeneous over the 
entire surface and in all spectral bands. 
The minimum surface was set empirically at 10-12 pixels i.e. 4 to 5 ha. 
Moreover the form of such small areas had to be more or less square in 
shape in order to reduce contamination by border effects due to pixels 
straddling limits. 
Spectral homogeneity was checked after location on NMAPW prints of the four 
spectral bands. This location was achieved by interpolation between recog- 
nized reference points ‘taking into account differences in scale and print- 
out deformations. This was greatly facilitated by the use of a B & L 
Zoom Transfer Scope which allows for anamorphic correction. Discrepancies 
between the LANDSAT data and the 1966 topographic map were checked in the 
field, always to the advantage of the former. 
4.3. Ascertainment of spectral signatures 
The data corresponding to the pixels of each training area were then 
entered in the STATS programme. With the radiance averages calculated 
it was possible to establish the radiance range for each category in each 
spectral band. Results are illustrated in fig. 2 and 3. 
These radiance ranges are the main input for the EXIO programme. The other 
statistical data derived by STATS were used as inputs for the CANAL programme. 
4.4. Assessment of land use distribution 
As radiance overtaps for the four categories retained, both on the March 
and the May scene, are rather small in band 5, its information was used as 
sole input for EXIO version I (fig. 5 and 7). 
The information on band 7 for the May scene was treated slightly different- 
lv by EXIO version 2. In this band there was indeed an interference of 
cultivated land with the other categories. The cultivated land pixels. 
well separable on band 5, were therefore eliminated prior to the separa- 
tion in band 7 of the other categories (fig.8). 
The CANAL programme was applied both to the March and to the May scenes. 
The main purpose was to compare the results obtained by a supervised 
classification programme makine use of the information in all four spec- 
tral bands with one using onlv the information that appeared as having 
the greatest diagnostic value (fig.6 and 9).