Full text: Proceedings of the Symposium on Global and Environmental Monitoring (Part 1)

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(BAUMGARTNER et al., 1988) of the satellite 
scenes. In the case of analog image 
interpretation, it is requested that a specific 
preprocessing, applying stretching techniques, 
is carried out. By optimizing all values 
indicating snow (all bright pixels) and 
disregarding all darker features, a clear 
separation of snow and ice can be reached, 
which then makes it easier to recognize and 
map the snow boundaries. 
The methods, their development and testing, 
are described in detail (HAEFNER & 
LAAGER, 1988; HAEFNER, 1990). Specific 
problems occur in areas with extended 
crevasses and ice falls. 
The delineated boundaries then are overlayed 
on large-scale maps (1:25'000 - 1:50'000), if a 
geometric correction was included. Otherwise 
the transference onto the map is carried out 
these features, since the spectral characteristics 
between the relative white snow, the 
brownish-white firn and the blueish ice are 
rather similar and the seasonal and diurnal 
variations quite significant. Therefore only 
when substantial parts of firn are exposed, a 
classification based on a spectral differentiation 
becomes possible. A careful selection of the 
test samples is crucial and should be 
undertaken by an experienced scientist only. 
So far we dispose of one good example of the 
Aletsch Glacier (Fig. 3) for separating firn, 
which could be verified in the field. 
Depletion curve 
For a better understanding of the melting 
process and its influence on mass balance and 
run-off regime a monitoring of the variation of 
the transient snowline during the melting 
period is necessary. 
A careful analysis of the course of each 
interpreted transient snowline with the contour 
lines on the glacier in the melting area will 
Fig. 3: Seperation of snow, firn and 
ice on Aletsch Glacier for Oct. 
14,1985 (classification by Dr. 
Markus KELLER and Shashi 
KUMAR) 
allow a correlation with a specific contour line, 
e.g. altitude. This figure generalizes the areal 
situation and excludes local influences by 
microrelief, deposits on the surface of the 
glacier (moraines) etc. This reduction of a 
complex situation to a specific contour line is a 
prerequisit to size the dynamics of the melting 
process by combining these different elevation 
figures into a melting curve (Fig. 2). At least 2 
to 3 reference images for each month during 
the melting period are needed for the 
construction of an accurate melting curve. Once 
it has been established for a glacier, the 
modifications appearing in the following years 
can be deduced from a limited number of 
interpretable satellite scences. 
Aeral measurements of the total surface of 
glaciers 
For the determination of the AAR the total area 
of the surface of the glacier has to be measured 
periodically, at least every second or third year.
	        
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