Proceedings, International Snow Science Workshop, Breckenridge, Colorado, 2016
INFRASOUND DETECTION OF AVALANCHES IN GRASDALEN AND INDREEIDSDALEN, NORWAY
Tore Humstad1*, Ørjan Søderblom2, Giacomo Ulivieri3,4, Stian Langeland5, Halgeir Dahle1 1Norwegian
Public Roads Administration, Molde, Norway, og Fjordane University College, Sogndal, Norway, 3iTem s.r.l, Florence, Italy, 4Department of Earth Science, University of Florence, Florence, Italy, 5Wyssen Norge AS, Sogndal, Norway 2Sogn
ABSTRACT: Infrasound technology for detection of snow avalanches has been tested in mountainous terrain in Norway over the two last winter seasons. Two valleys, Indreeidsdalen and Grasdalen, were selected as test localities for the infrasound arrays because they both are exposed to avalanches from different aspects and several paths. Hence, a detection of an avalanche in one path would be a crucial indicator of the danger also from other paths. Before 2014, Norwegian authorities have traditionally made little use of technical measures to automatically detect avalanche and landslide activity, and infrasound detection of avalanches had not been tested in high latitudes with sparsely vegetated terrain. Hence, the Norwegian Public Roads Administration wanted to test infrasound both for technical and strategically reasons. In addition to temporal recognition of avalanches, spatial analysis of the avalanche paths were made based on the azimuthal location of the infrasound sources and a GIS study of the surrounding terrain. The results from the two seasons are promising, and this article summarizes some developments. KEYWORDS: infrasound, avalanche detection, forecasting, IDA
1. INTRODUCTION
Mendenhall, 2004; Scott et al., 2007; Ulivieri et al., 2011; Kogelnig et al., 2011; Havens et al., 2014; Thuring et al., 2015; Marchetti et al., 2015). After the initial works with single infrasound sensors (e.g., Bedard, 1989), the use of infrasound arrays techniques (an antenna of infrasonic sensors deployed in the field) has improved significantly the detection capability at a source-to-receiver distance of ~ 2 km (Scott et al. 2007; Ulivieri et al., 2011) and dedicated algorithms for near real-time automatic identification of avalanche events have been tested and validated in Austria and Swiss (Marchetti et al., 2015; Thuring et al., 2015).
Natural snow avalanches are clear signs of snow pack instability. The monitoring of snow avalanche activity is then crucial to constrain and validate forecasting models. Visual observations are mainly used to evaluate avalanche activity, but the strong limitations due to visibility conditions allow us to have only a discontinuous dataset of avalanche events. This limit prevents us to make reliable comparison between avalanche activity and forecasting models and then preventing us to improve the procedures used for the assessment of avalanche risk (Schweizer et al., 2003). Continuous monitoring of snow avalanche activity regardless sunlight and visibility condition is hence the challenge to significantly improve avalanche forecasting (Schweizer et al., 2013). Among other, the use of infrasound methodology for avalanche monitoring and characterization has increased rapidly during the last decades (Bedard, 1989; Chritin et al., 1996; Adam et al., 1998; Comey and
Since Oct. 2014, the Norwegian Public Roads Administration (NPRA) started to test the infrasound array methodology in the framework of NIFS Project, an Interdepartmental Research Rrogram on Natural Hazards (Dolva et al., 2016). Here we present the preliminary results achieved by infrasound array monitoring of avalanches in two different sites during the last two winter seasons.
* Corresponding author address: Tore Humstad, Norwegian Public Roads Administration, Fylkeshuset, 6404 Molde; tel: 0047-901 40 850; e-mail:
[email protected] 621
2. TEST LOCATIONS IN NORWAY 2.1 Background Before this experiment, Norwegian authorities had made limited use of technical measures to automatically detect avalanche activity, and more in general, infrasound detection of avalanches had not been tested in high latitudes with sparsely vegetated terrain. On Oct. 2014, NPRA started a 2-years-long experiment aimed to test the feasibility of infrasound technology to detect natural avalanches in automatic. Two IDA® systems (Infrasound Detection of Avalanche) were then installed at Indreeidsdalen and Grasdalen sites (Fig.1). 2.2 Indreeidsdalen Indreeidsdalen is a north-south aligned valley with its base on 500 m a.s.l. surrounded by mountains reaching up to 1600 m a.s.l. The valley’s county road Fv63 is exposed to 14 avalanche paths at both sides of a road segment of 4 km. On the average, this road segment is closed 4-5 days every winter because of avalanches or avalanche danger.
Fig. 1: The two test locations (blue dots) chosen to test the infrasonic array methodology in Norway. 3.1 Instrument configuration
2.3 Grasdalen
IDA® consists in a four-elements infrasound array with a triangular geometry with 150 m aperture. Each array element is equipped with a differential pressure transducer (iTem-prs0025f) with high sensitivity (200 mV/Pa), broad-band frequency range (0.01-50 Hz) and low noise level (
