Avalanche detection – Is automatic detection possible?

Initial situation

In which locations have avalanches occurred? The ability to answer this question is of great significance to safety authorities and avalanche warning services. Thus far, observers (mountain guides, backcountry skiers etc.) have been reporting natural avalanches, but generally only after a delay and provided that visibility is good. Examining the effectiveness of explosions can likewise take place only to a limited extent if visibility is poor and at night. Although several automatic avalanche detection systems capable of operating in any visibility already exist, their functionality is restricted.

Against this background, in spring 2009 the Swiss Avalanche Warning System Association (SILS) and the National Environmental Agency (BAFU) launched a three-year avalanche detection project under the auspices of the SLF. The aim of the project is to examine a variety of systems for automatically detecting avalanches in several locations in Switzerland (Fig. 1) and thus to monitor not only an individual avalanche path, but an entire section of terrain (distance ≥ 2 km, angle ≥ 40°). Since avalanche detection systems are safety systems, they must also comply with the RAMS (reliability, availability, maintainability, safety) standard described in DIN EN 50126.

In cooperation with local avalanche authorities, the SLF is testing acoustic detection systems (microphones), and detection by measuring the echoes of electromagnetic waves (radar) and by means of electromechanical transducers (seismometers or geophones). The results are to be used to produce guidelines and criteria for the deployment of the various systems.

The map below (Fig. 1) shows where the different systems are installed and undergoing testing.

Fig. 1: Map of locations where avalanche detection systems are being tested.

Differing reliability of systems

Experience gathered during the last two winters shows that all three technologies (acoustic/radar/seismic) are capable of detecting avalanches automatically.

It was also found that the reliability and coverage of the individual systems differ.

Fig. 2: Schematic of a detection system, illustrating possible sources of interference/problems/hazards.

Avalanches can be detected acoustically from a distance of up to 6 km. Reliability cannot be ensured at present, however, because of the numerous spurious signals. In particular, the interference is attributable to all infrasonic sources (wind, aeroplanes, helicopters, transformer stations, cableways etc.). These give rise to both false detection and a failure to detect some avalanches.

Radar detection, on the other hand, is a very reliable means of detecting activity in an individual avalanche path. The radar technology that is available for avalanche detection purposes (performance range, power consumption, cost) is currently able to cover a path of around 200 m with a range of 2 km. This does not yet comply with the specifications of an avalanche detection system as stipulated within the framework of the project.

Geophones are likewise capable of detecting avalanches. Their installed location is critical, however, because the propagation of seismic waves depends on the density, shear modulus and bulk modulus of the medium. The best location for geophones is the avalanche slope itself, but this is not always practicable. Geophones are primarily useful in combination with other detection systems.

None of the three systems is suitable for the operational monitoring of extensive areas at present because they are still prototypes or undergoing evaluation.

Outlook

For the 2011/2012 winter season, the technologies have been refined to some extent and combined with each other. The measurements taken in the 2011/2012 winter are expected to show which technology and configuration satisfies the criteria for an operational avalanche detection system in compliance with the RAMS standard. In future, development resources are to be focused on the identified solution.