Fraunhofer Institute for High Frequency Physics and Radar Techniques FHREnsuring safety in mountainous regions requires reliable avalanche monitoring. A feasibility study conducted by Fraunhofer FHR demonstrates the technological and operational advantages of passive radar compared with existing monitoring methods. Of particular relevance is the use of modern satellite mega-constellations as illumination sources.
When snow falls heavily from the sky or temperatures rise rapidly, avalanche warnings are issued in many areas. To mitigate risks to people and infrastructure, controlled detonations are sometimes carried out. However, it then becomes crucial to verify whether the avalanche was actually triggered as intended. For emergency services and operators, this verification is a key component of risk management. Likewise, the continuous monitoring of naturally occurring avalanches is essential for public safety.
Radar technologies are widely used for this purpose: they enable continuous, weather-independent remote monitoring. The challenge is that avalanches typically occur in remote terrain where terrestrial infrastructure is either absent or can only be installed at considerable expense.
Starlink and Co. as Signal Providers
Passive radar is therefore a particularly suitable technology for avalanche detection in hard-to-reach regions. In contrast to conventional radar, this system does not transmit its own electromagnetic energy but instead exploits existing broadcast or cellular communication signals. The advantages include high signal availability, low cost, simple installation, and license-free operation. Moreover, thanks to the motion of the signal sources, it is possible to realize bistatic synthetic aperture radar (SAR) from a stationary receiver.
However, there is also a drawback: in many remote mountain areas, broadcast signals are not available. In the project SLIDE (“FSS-constellations for avalanche detection with passive radar”), Fraunhofer FHR therefore relies on the signals of satellite-based illumination systems, such as the Starlink and OneWeb mega-constellations with fixed-satellite services (FSS). These systems enable extensive and continuous illumination of remote mountain regions, since multiple satellites simultaneously cover the areas of interest from different viewing angles.
Simulation and Field Experiments
On behalf of ESA-ESTEC, researchers at Fraunhofer FHR are addressing this question in a feasibility study. Using topographic data, they are developing a realistic simulation environment to analyze the detectability of avalanches.
“Based on the topographic data of a mountain, we developed a simulation environment in which we simulated avalanches and analyzed whether they could be detected using Starlink signals,” explains Diego Cristallini, Group Leader of Passive Radar in the MFR department. To validate the promising simulation results in practice, the researchers are also using their passive radar system to detect small controlled “landslides” in a former basalt quarry on the Rhine near Remagen. The quarry is being backfilled with soil; the avalanches occur when an excavator dumps its load into the still open pit. These experiments serve as an experimental validation under realistic conditions.
Results: Potential for Operational Deployment
“Both the simulations and the field experiments show,” Cristallini concludes, “that passive radar using signals from satellite mega-constellations is well suited for avalanche detection.” This provides a powerful, scalable, and cost-effective approach that opens up new possibilities for reliable avalanche monitoring, particularly in regions with limited infrastructure.