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The new Pulse Doppler radar measures the speed of avalanches by using frequency shift. The frequency shift phenomenon in the sound of a moving object was first described by the Austrian physicist Christian Doppler. A typical example of this phenomenon is an ambulance with its sirens blaring as it approaches you at high speed. As the ambulance passes you, the sound of the siren will change pitch and become darker. The new radar will provide NGI with more information that will make it easier to monitor and research avalanches.

The radar is on loan from NGI’s partner the Austrian Research Centre for Forests (BFW).

"Until now, NGI has been using a Doppler radar that was transported into the avalanche area and manually switched on by a PC. In practice the old radar only recorded avalanches triggered by us. This was because it was not possible to leave it on except when performing our planned measurement campaigns, says Senior Avalanche and Rockslide Specialist," Dr Peter Gauer.

The new radar is operational 24/7 throughout the winter and will also detect avalanches occurring naturally.

The new Pulse Doppler radar was used in connection with the successful experiment carried out on 11 April 2021.

Developed and tested in Austria

The radar was developed, built, and tested in Austria. It will record the speeds of avalanches at different points along the avalanche path.

“With the new radar we are hoping to obtain more and better speed measurements. These will, among other things, be important for the development and validation of numerical avalanche models. From a Health and Safety perspective, we will no longer have to enter exposed terrain in order to obtain measurements," says Dr Gauer.

New weather station and scanner for snow depth

In addition to the new radar, a compact weather station and LIA laser scanner have been purchased. The laser scanner measures growth in snow height from snowfall or wind-drifted snow. The scanner can also provide information about the fracture heights in the release area.

The scanner is mounted on the Wyssen avalanche tower above Ryggfonn’s release area. The instruments will provide better details about weather parameters and snowpack in the release area, for example, the actual initial avalanche volume.

“This will make it easier to choose a good time for initiating a measurement campaign. A new weather station near the instrument cabin in Grasdalen is providing additional measurements. Our weather stations will also help us to better understand how the weather and snow properties affect avalanche activity and avalanche dynamics," says Dr Gauer.

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Research for the future

The aim of NGI's avalanche research at Ryggfonn is the development of better tools for hazard zone mapping, which constitutes a part of land use planning that helps to delimit where infrastructure can be established safely without being exposed to avalanches. It is therefore important to have as much information as possible about avalanche behavior in order to be able to assess potential hazard in planned development areas.

“Before our last experiment on April 11, a few smaller natural avalanches were recorded by our new Doppler radar. All the data from the experiment and naturally triggered avalanches will now be evaluated during the summer. It is important that we obtain more measurements of different snow conditions and enough repetitions to enable generalisation of the results," says Dr Gauer.

Parts of this research are being funded by the Norwegian Ministry of Petroleum and Energy under the "R&D Avalanche 2020-2023" project grant awarded to NGI and administered by the Norwegian Water Resources and Energy Directorate (NVE).