A ue ess ss Ces ES ee CL KA ECTETUR ail
--9*
Bottom: Ratio values relative to the dry snow scene of 16.01.93.
the snowfree scene of 10.07.93.
The two sequences of wetness maps for the
melting period 1993 as deduced from the SAR-
data are represented in Fig.4. Applying the
change detection method, an almost snowfree
scene (10.7.93) respectively an almost com-
plete dry snow scene (16.1.93) were used as
reference to calculate the ratio values. A
threshold value of -0.5 dB was selected to
achieve comparable results. The pronounced
topography allows an easy localization of the
lower snow boundary, and hence a recon-
struction of the total snowcover. Furthermore,
the ascending of the snowline and the increas-
ing extent of the wet snow with the progres-
sion of the melting season can be recognized
clearly. A comparison of the two sequences
allows the conclusion, that both reference
scenes are suitable for such a change detec-
tion and produce quite similar results.
Fig. 5. illustrates the results of the simple
fusion model, showing the subset of the RGB
images before and after the fusion pocedure.
Fig. 5: Testsite GRISONS: Subset of RGB image
before (left) and after (right) data
fusion process. The situation of the
snowpack is representative for mid-
May, 1993
7. CONCLUSIONS
EO data still are most suitable for snowcover
mapping in high mountain areas. The sensor
system with its specific ground resolution has
to be selected according to the areal extent
of the investigated area. But for monitoring
the melting process SAR-systems are an absolu-
te necessity, to firstly reach a continuous
time series, and secondly to retrieve certain
snow parameters, in particular the wetness.
Data fusion techniques offer the best potenti-
al to combine these two systems, and to gain
more accurate and informative results. The key
element is to make SAR data applicable and
operational in mountain areas by using the
ORA/MORA approach. These new methodological
tools open up many additional possibilities
for geoecological research topics and applica-
tion in high mountain regions.
ACKNOWLEDGEMENT
This research project has been supported by
the Swiss Academy of Science (Project 20-
41889.94). The ERS-1 SAR data were made
available for AO.CH2 experiment by the Europe-
an Space Agency ESA.
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