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Considering the continuous change which takes place in the environment 
it is clear that a proper description of the environment should include change 
phenomena. The ERTS shows a potential to provide some of this data, in spite 
of its relatively low resolution, for example the formation and melting of aufeis 
or icings. Aufeis represents temporary, above ground storage of ground water 
discharged during winter; aufeis as small as 100 m2 can be identified (Van 
Everdingen, 1974). An aufeis development and melting is shown in Fig. 4 E, F. 
In Fig. 2 E, F, the changing conditions in a carex fen type wetland which is 
surrounded by raised drumlins show spring meltwater storage and late summer 
conditions. 
Repetitive airborne surveys of selected ecosystems using multiple sensor 
combinations are important for the description of the more dynamic ones. Comparison 
of photographs which were taken within a ten-year and a twenty-year interval made it 
possible to determine the rate of melting of perennially frozen peat landforms as 
a function of time, and environmental parameters such as climate, drainage, fires, 
etc. (Thie, 1974). One could expect that forest fires on peat plateaus in the 
sensitive southermost fringe of the discontinuous permafrost zone would increase 
the rate of melting, however the study showed no measurable change. These perma 
frost ecosystems are stable enough to survive fires and possibly some human 
activities. 
By using ERTS the mapping of forest fires is a simple task as demonstrated 
by the Ontario Centre for Remote Sensing (Zsilinszky,1974). Mapping of recently 
burned-over areas in Northwestern Ontario by means of conventional airborne techni 
ques cost approximately $13,500; ERTS mapping provided the same amount of data 
for about $500.00. Annual mapping of forest fires can be done for relatively 
small amounts of money. Considering the number of fires in Canada (1973: 5,087 
fires and about 835,000 hectares) this can amount to significant benefits eveVy 
year. 
McQuillan, 1973, describes the benefits of monitoring sea ice for 
transportation in northern Canada and estimates benefits of about $4 million 
annually in 1975 which will increase to about $12 million in 1990 if ERTS and 
NOAA data can be rapidly transmitted to the user, for example to ships. Benefits 
can be increased to over $100 million annually in 1990 if the remote sensing 
systems are extended to include ice thickness measuring sensors, a satellite with 
microwave imaging sensors on board and a satellite data relay system. In any 
monitoring program using remote sensing we should therefore not only be concerned 
with the acquisition of data and its interpretation, but also with the design of 
a system for rapid data transmission to the user. 
Monitoring of water conditions from a satellite may be especially 
promising for the characterization and mapping of water bodies. Water conditions 
are very dynamic. Different researchers have shown correlation between ERTS 
digital data and suspended sediment, chlorophyll, turbidity, etc. Ice melt and 
break-up can be related to current flows (Fig. 4 A, B), while suspended sediments 
and humic water can be related to surrounding land materials (Fig. 4 C, D). 
ENVIRONMENTAL IMPACT ASSESSMENT AND PREDICTION 
Base line information which describes the natural conditions of the 
environment is essential to impact assessment and impact prediction. Without 
this data change cannot be measured or adequately predicted. For most areas 
in Canada, the type of base line information which is needed does not exist.