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If resource information is available, it was gathered on a single disciplinary 
basis and the study and measurement of natural change phenomena was not in 
cluded. An indication of the lack of adequate 'historical' data is shown by 
the airphoto coverage of Canada. Most of the country was covered once and 
selected parts of the developed areas were covered more frequently. Except 
for the ERTS coverage this leaves many areas in the north, where presently 
large scale developments are contemplated, without data on natural environ 
mental change. 
To predict impact it is necessary to study the effect of similar 
activities in the past on similar ecosystems in similar ecoregions. The amount 
of historic data, as discussed earlier, is quite limited and in many situations 
we may not be able to learn from the past. However, natural models may exist 
which may be indicative of the situation after planned actions have taken place. 
These models should be selected on the basis of ecological similarity between 
the model and the expected future situation in the areas where the change will 
occur. For example, South Indian Lake in Northern Manitoba is a part of a large 
hydroelectric development. Fig. 4 C shows the present situation as indicated by 
an ERTS band 5 image. The Lake will be flooded; based on a detailed biophysical 
survey it is predicted that the amount of eroding clay shoreline will increase 
from about 5% to about 75% and this is similar to the present situation in the 
highly turbid South Bay area. Based on this similarity one could predict that 
the turbidity levels in the rest of the Lake may reach the levels of South Bay. 
The ERTS satellite is well suited for the purpose of finding such 
representative natural models especially in water and it can also monitor man 
made change in a general way. It may act as a surveillance or warning tool that 
some impact is occurring, but it will probably not provide adequate detail for 
impact assessment (Fig. 5 D, F, G). Much of this work will have to be done 
from aircraft by means of special sensors and supported by ground truthing. 
However, ERTS can provide the basis for extrapolation of this information over 
a large area. 
Almost any surface change resulting from man's activities can be 
monitored by using aircraft and satellite remote sensing and ground truthing: 
land use change, crop response, urban sprawl, new roads, hydrolines, logging 
areas, forest regeneration, etc. Fig. 3 shows a number of examples of smelter 
smoke damage, logging areas and new road development. ERTS can demonstrate 
some of the cause and effect relationships related to land management; Fig. 2 
shows the connection between clearing of forest cover, erosion on sloping lands 
and spring flooding in lowlands in the Whitmud River watershed. Imagery from 
the ERTS-1 satellite has been used to revise small scale maps in the wilderness 
areas of Canada. New roads, railroads, hydroelectric transmission lines and 
reservoirs which are all part of the development of the north can be detected 
on ERTS imagery and can be plotted with sufficient accuracy for the revision 
of 1:250,000 topographical maps and 1:500,000 aeronautical charts (Fleming, 1974). 
ENVIRONMENTAL PROTECTION SURVEILLANCE 
While surveillance in support of resources management activities is 
conducted to determine the true ecosystem impacts, surveillance is also carried 
out to determine the effectiveness of measures which are being used to protect 
the environment.