allgemein anerkannt, daß kleinmaßstäbige Aufnahmen in Kanada zur Unterstützung 
der Geologen bei Kartierungsvorhaben benötigt werden, wobei der Maßstab 
1:250,000 eine besondere Rolle spielt. Durch sein beschränktes Bodenwiedergabe- 
Auflösungsvermögen wird sich das ERTS-Aufnahmesystem für diesen Zweck 
wahrscheinlich als nur teilweise befriedigend erweisen. 
INTRODUCTION 
Canada is large by any standards. Occupying approximately 10% of the 
earth's surface, it requires about 700 ERTS images to cover the entire 
country. The geology is also very varied, including some of the most ancient 
and some of the most recent rocks in the world. It is practically self- 
evident that any satellite system capable of producing images should be 
examined most carefully for possible geological applications. 
The Geophysics and Geochemistry Division of the Geological Survey of 
Canada is involved in two aspects relating to the evaluation of ERTS imagery. 
One of these is to put together a collection of high quality ERTS imagery, and 
another is the selection of about 50 images representing as many of the 
geological environments of Canada as possible. This selection is to be 
published. Each image will be accompanied by a short descriptive statement 
written by a geologist familiar with the area, relating the geological 
significance of the area. 
This exercise has been a means of introducing some 40 geologists to ERTS 
imagery and it is hoped that the feedback from these geologists may be helpful 
in determining where ERTS image studies may be most usefully applied. So far, 
much of the information return has related to problems of interpretation. How 
does the analysis of ERTS imagery differ from that of aerial photography? 
Which ERTS band is most useful for what? What about colour imagery? This paper 
is written to provide some of the answers to these questions, together with a 
brief statement on the potential applications of ERTS. Included also is a 
small representative selection of colour images. 
THE RELATIONSHIP BETWEEN AERIAL PHOTOGRAPHY AND ERTS IMAGERY 
Aerial photographs are normally interpreted using three different 
approaches. Listed in order of importance, these are a) stereo-analysis of 
the morphology, -b) analysis of textures and patterns in the image, and 
c) study of differences in grey tone or colour. 
Stereo-analysis of ERTS imagery using material from adjacent runs can be 
achieved in areas where the topography varies by about 600 metres or more. 
Unfortunately the results are not usually very satisfactory, partly because of 
limited resolution and partly because of unfavourable base/height ratios. 
Thus the examination of ERTS imagery really centres about image texture and 
differences in grey tone or colour.