Optical snow level monitoring in avalanche paths in Saxon

Challenge

The Pierre Avoi is an imposing rock face culminating at 2470 m and which towers above the Rhone Valley, between the commune of Saxon and the ski resort of Verbier. In summer as well as in winter, the Pierre Avoi is a popular route for hikers or backcountry skiers. In winter, it is not uncommon for the avalanche paths located northwest of the Pierre Avoi to be heavily snowed in and for major avalanches to occur naturally, threatening some of the houses and roads of the commune of Saxon located below. In order to secure the infrastructures, the commune of Saxon collaborates with the security service of the slopes of the resort of Verbier – 4 Valleys in order to trigger avalanches when necessary, during the winter. This strategy allows to avoid too important snow accumulations, which could cause the triggering of big avalanches. In order to know when the snow level was high enough to trigger avalanches, graduated poles were installed. The snow level was read using binoculars from the Rhone valley. Since the trigger zones are located in an area that is not easily accessible and visibility from the valley is not always guaranteed in winter, the local authorities needed additional information to help manage the avalanche danger in the region.

Camera installed to monitor the snow level below the Pierre Avoi.

Solution

The commune of Saxon mandated the engineering firm Nivalp and GEOPREVENT to provide a technical solution. Since graduated poles for reading the snow level already existed at key locations in the various corridors of interest, GEOPREVENT proposed to develop a camera specially adapted for taking pictures of the snow cover and capable of operating reliably in alpine and exposed conditions. To do this, the existing PROCam system was adapted in several
ways. First, an optical filter was mounted on the camera lens to reduce reflections from the sun and increase contrast. In addition, a power supply system including a solar panel
with a battery and low energy consumption components were carefully selected. In addition, GEOPREVENT has developed a system with a snow blower that allows the lens to be cleared of snow on a regular basis when it is obstructed by snow. These different developments allow the
system to take pictures with an hourly cadence during 2–3 weeks of bad weather, facilitating the decision making of the municipality concerning artificial avalanche releases.