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LIMITS OF ERTS IMAGERY AS A TOOL FOR STUDYING 
THE BREAK-UP OF THE MACKENZIE RIVER, N.W.T. 
EXPERIENCES IN 1973 AND 1974 
D.A. SHERSTONE, K.C. ARNOLD AND D.K. MACKAY 
GLACIOLOGY DIVISION, ENVIRONMENT CANADA 
ABSTRACT 
The 1972, 1973 and 1974 spring break-ups of the Mackenzie 
River have been recorded by aerial photography. ERTS imagery of 
the 1973 and 1974 break-ups has been examined to determine to what 
extent it can replace or supplement air and ground records. 
In 1973 "Quick-Look" prints were examined with reference 
to 1:250,000 scale maps in an attempt to follow the progress of 
break-up downstream. The low resolution of these prints limited 
the usefulness of this approach. 
In 1974 a Bausch and Lomb Zoom Transfer Scope was used to 
plot seven cloud-free "Quick-Look" frames on 1:250,000 map overlays. 
The results were again discouraging, because: 
- One could not discriminate between land areas and adjacent 
open water; 
- many islands shown on 1:250,000 maps could not be identified; 
- differences in position of some islands from one image to 
another were detected; 
- there are unexplained distortions in shorelines when ERTS 
imagery was superimposed on maps with the Zoom Transfer 
Scope; 
- it was not possible to distinguish between different ice 
types, or between moving ice and fast ice; and 
- interpretation was not improved using a colour densitometer; 
We conclude that ERTS "Quick-Look" imagery presently available is not 
a viable alternative to air and ground based break-up studies, and is 
of limited usefulness as a supplementary aid.