Avalanche radar Holmbuktura, Norway
Norway is characterized by hundreds of fjords along its coastline and mountain ranges with peaks above 2000 m above sea level. The steep fjord slopes are prone to natural hazards, particularly avalanches during winter. Many communities are located at the sea-side and heavily depend on roads along the shore for transport of people, goods and services. Holmbuktura is located in Northern Norway about 1h by road from Tromsø. The access road to the villages leads through a notoriously avalanche-prone area and road closures are necessary several times every winter. Statens vegvesen, the Norwegian Public Road Administration, provides avalanche danger assessments and acts as advisor to the local authorities in terms of preventative road closure and their reopening. Road closure periods should be minimized and isolation of the already remote villages should be avoided whenever possible. However, the road must be safe for passage at all times – a difficult task for the decision makers.
In order to provide a cost-effective and reliable solution to this problem, Statens vegvesen chose to closely monitor the slope, detect avalanches in real-time by radar and automatically close dangerous sections of the road with traffic lights. The project requirements were challenging considering the location, extent and distance of the slope to be monitored. Whereas avalanche radars in mountain valleys are typically mounted on the counter slope, an equivalent approach is not feasible in this case due to the width of the fjord. Simulations for the Holmbuktura area revealed the northern bay side as ideal location for a long-range avalanche radar. We developed a radar solution with reach of up to 4 km to guarantee maximum slope coverage. The radar opening angles of 90° horizontally and 15° vertically allow for coverage of an even larger than the region of interest – in total 4 km². The setup includes a PTZ-camera (Pan-Tilt-Zoom) that automatically captures avalanches or smaller events of interest. It can further be used to remotely gain an overview of the situation at any time. All data and live pictures are accessible via the online data portal, where detected avalanches are also displayed on the area map. Since installation in February 2017, more than 20 avalanches have been detected, including small events in up to 3.3 km distance from the radar.
The initial trial period of the avalanche radar has exceeded all expectations by Statens vegvesen so far. As geologist Andreas Persson, who is in charge of the project on behalf of Statens vegvesen, summarizes: “Unlike other years, we have not had any major avalanches in Holmbuktura this winter (2017). However, the radar has captured many small events on the slope very well. Both, the radar range and the level of detail have exceeded our expectations by far.” The goal is to add traffic lights or barriers on both ends of risky road sections that are automatically controlled by the avalanche radar system. Further testing and experience will be gathered in the coming season. So far the results are very promising – also for further locations in Norway.
Avalanche detection examples
During the night of 5 December 2017, the avalanche radar in Holmbuktura (Tromsø, Norwegen) detected six avalanches of which one reached as far as the road covering it with 1.5 m of snow. Our avalanche detection system correctly identified all avalanches and marked their tracks in the online map. All events were recorded by a PTZ (Pan-Tilt-Zoom) and a thermal imaging camera. The furthest away avalanche broke off at a distance of 3.5 km. The largest avalanche (video below) took 45 s from detection to the road. Despite the location of Holmbuktura north of the polar circle, the avalanche is visible even at 5:30 AM in the morning due to the full moon. The thermal images show that the avalanche is warmer than its surrounding. This is due to two reasons: on one hand the fact that motion produces heat and on the other the avalanche brings snow from deeper, warmer layers to the surface.
Automatic road control is not set-up yet at this location as the system currently runs in the trial phase.