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The imagery arrived at ITC, Enschede, in the month of May 1973 in the form of 
70 mm black and white negatives, and b & w negatives and diapositives of 23 cm 
format in 1 : 1 , 000 , 000 scale. At that time the fieldwork had already started and 
the whole of the Soil Dept, had moved to the test site area in Spain. The Photog 
raphy Dept, of ITC made positive paper prints of the negatives, both as contact 
prints and enlargements of the originals to scales of 1 : 500, 000 and 1 : 250, 000; 
for technical reasons the enlargement to the 1 : 250, 000 scale was limited to only 
a part of the area (fig. 2 ). 
Only 3 of the 4 bands were treated in this way, because the original imagery 
corresponding with band 4 of the MSS of ERTS -1 was of too poor quality for en 
largement. All the products were despatched to the investigators in the field who 
received them at the beginning of June, and fieldwork continued until the end of June. 
2.2 Study of black and white paper print enlargements 
In the early stages of fieldwork the black and white paper prints were examined 
with respect to the quality of photography, resolution, and appearance of various 
landtypes on different bands. Traverses were completed along main roads, a check 
was made to see how each land unit appeared on each band, and how far a distinction 
could be made in the black and white imagery. Furthermore, the limits of resolution 
and the influence of different elements such as vegetation cover, agricultural prac 
tices, texture of top soil, frequency of rock outcrops, etc. , were investigated. 
Most of the work was done using the 1 : 250, 000 enlargements, the others being 
of rather too small a scale for use in the field. In the office a visual interpretation 
was conducted both during the fieldwork period and afterwards at ITC. Initially a 
mirror stereoscope was used with the idea of blending the images of two bands, 
with the expectation of improving the amount of information received simultaneously, 
and consequently the validity and accuracy of the interpretation lines. The large dif 
ference in contrast between bands created fatigue problems. 
The use of a red and green filter for each eye reduced the fatigue somewhat but not 
enough, and unfortunately at the same time the filters created problems of illumi 
nation because of the different levels of illumination required to compensate for the 
differing densities of the filters. Thus, in the end the mirror stereoscope was 
abandoned and the interpretation was done directly and monoscopically on the paper 
prints of different bands using a magnifying glass. The resulting interpretation maps 
were compared with the existing soil maps and other available information to find 
the possibilities of delineation for various soil mapping units.