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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.
