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0
0 50 100 150 200 250 300 0 50 100 150 200 250 300
greyvalue greyvalue
Figure 3: Luminance values of an image at night with illumination (a) with yellow balls and at night without
illumination (b). Greyvalue 0 corresponds to black, greyvalue 255 corresponds to white in each
histogramm. It is obvious that at night without illumination it not necessary to work with colors.
Contrast between bright balls and dark surrounding is clear enough to be determined by the computer
(b).
from the previous images and predicts the search strategy for the new one.
ACKNOWLEDGEMENTS
This work is supported by the Swiss National Fonds in the programme *Climate Change and natural hazards".
Further thank is given to Walter Caviezel, Urs Suter and Angelo Maccagnan of the Swiss Federal Institute for
Snow and Avalanche Research for their support.
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Kobayashi, D. (1987). Snow accumulation on a narrow board. Cold Regions and Technology, 13:239-245.
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Maas, H.-G. (1992). Ein photogrammetrisches System zur Bestimmung von Geschwindigkeitsfeldern in turbu-
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Schmidt, R. A. and Pomeroy, J. W. (1990). Bending of a conifer branch at subfreezing temperature. Can. J.
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Tennyson, L. C., Ffolliott, P. F., and Thorud, D. B. (1974). Use of time-lapse photography to assess potential
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IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995