WSL Institute for Snow and Avalanche Research SLF

First ever large-scale satellite detection of avalanches

10.12.2019  | Claudia Hoffmann | News SLF

For the first time, researchers from the WSL Institute for Snow and Avalanche Research (SLF) have mapped an extreme avalanche period using optical satellite images, producing the fullest, most comprehensive data set on avalanches during an extreme period anywhere in the world.

This avalanche occurred during the period around 22 January 2018 to the south of the Tiefenstock mountain in the canton of Uri. The left-hand image shows a very clearly recognisable avalanche on the SPOT6 satellite photo, and the right-hand image shows the mapped outline (in blue). Image: SPOT6 data ©Airbus DS 2018

Documenting avalanches as accurately and extensively as possible is important, e.g. for improving avalanche forecasts or reviewing hazard maps. Normally, information about avalanches comes from reports by individual observers or from helicopter overflights, but these sources cannot provide a full picture. No comprehensive mapping had been carried out previously, especially of periods characterised by exceptionally frequent and large avalanches.

But now SLF researchers, working in collaboration with swisstopo, have for the first time tested the use of satellite data to document an extreme avalanche period. To this end, shortly after repeated heavy snowfall in January 2018, the SLF commissioned the SPOT6 satellite to record images with a resolution of 1.5 metres in the visible (red, green, blue) light spectrum and near-infrared region, covering an area of 12,500 square kilometres, i.e. most of the Swiss Alps. SLF employee Elisabeth Hafner analysed the images by hand, recording - among other things - the outlines, types and sizes of all detectable avalanches, 18,737 in total. This work was part of the 2018 event analysis, the findings of which have now also been published in the journal "The Cryosphere".

Suitable for mapping large areas

The embankment (marked in red) in the Lötschental above Wyssenried in the canton of Valais was built after the avalanche winter of 1999 to protect the lower-lying avalanche barriers and the local community (a 1999 avalanche destroyed large parts of the defensive structure). The avalanche mapped here was triggered artificially. Similar in size to the one that occurred in 1999, it was fully diverted by the embankment, as the satellite images impressively reveal. Image: SPOT6 data ©Airbus DS 2018

To check whether the outlines of avalanches on the satellite images had been correctly identified, the researchers compared a sample with photographs taken during helicopter overflights. Hafner's conclusion? "The method is reliable and suitable for the large-scale mapping of extensive areas". The captured data will now be incorporated into the SLF's avalanche cadastre and other databases and will help, among other things, to test the effectiveness of protection measures taken after previous avalanche winters. The satellite images also afford an overview of resulting forest damage and serve to check danger levels forecast in the avalanche bulletin and improve avalanche simulation models such as RAMMS.

The satellite mapping was repeated in the January 2019 avalanche period, and may be used again during future extreme events. However, it has so far proved a labour-intensive process, with the outlines of individual avalanches having to be drawn by hand on the satellite images. For this reason, a master's thesis will investigate the potential for at least partially automating the mapping procedure. In addition, in collaboration with the Earth Observation and Remote Sensing Group at ETH Zurich's Institute of Environmental Engineering, the SLF is exploring the possibility of mapping avalanches by radar satellite. Radar satellites have the advantage of being weather-independent since they can take pictures even when the sky is overcast. Initial results are promising.

 

 

The map shows the proportion of land per square kilometre (in percent) overflowed by avalanches. Image: SLF

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WSL and SLF provide the artwork for imaging of press articles relating to this media release for free. Transferring and saving the images in image databases and saving of images by third parties is not allowed.