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| Titel |
Microtomography of layered snow samples and weak layers |
| VerfasserIn |
Margret Matzl, Martin Schneebeli, Daniel Steinfeld, Stephen Steiner |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048195
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| Zusammenfassung |
| During the last 10 years X-ray microtomography (micro-CT) has proven to be the first
efficient method to measure the true three-dimensional (3-D) structure of snow on the ground.
Micro-CT is used to reconstruct 3-D microstructures as a source for numerical simulations, to
conduct long-term observations of metamorphism or the behavior of snow under stress and to
derive macroscopic parameters describing the microstructure of snow like specific surface
area (SSA) or density. However, micro-CT was confined to small and predominantly
homogeneous samples with a typically evaluated size of 5 x 5 x 5 mm3. One reason for the
small size was the limited computational power, the other the sample preparation.
Based on the replica method for 3-D micro-CT samples introduced by Heggli et
al. (2009), we are now able to visualize snow samples up to 70 mm height, and
about 10 mm diameter, with a resolution of 10 ìm. Because inclusion of small air
bubbles during the casting process can not be avoided, we make two scans, one
before and one after sublimation, the two scans are then registered and subtracted.
After image segmentation and morphological image processing the replica can be
analysed in the same way as direct snow measurements. We reconstructed highly
fragile snow packs, like new snow, buried surface hoar and other weak layers. The
observable structure is 10-15 times longer than in previous samples. The samples show
a fascinating new image of how complex snow layers are. For layered samples
the parameters like SSA are calculated using a sliding window. This results in a
high resolution vertical SSA-profile of the snow sample instead of one averaged
value. We think that such 3-D reconstructions of the snow microstructure could be a
useful tool both for practitioners and researchers to improve the understanding of
snow properties, snow metamorphism, and fracture processes during avalanche
formation.
Heggli, M.; Frei, E.; Schneebeli, M., 2009: Instruments and Methods. Snow Replica
method for three-dimensional X-ray microtomographic imaging. J. Glaciol. 55, 192:
631-639. |
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