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Abstract
Wind can create even greater unstable accumulations of snow in mountainous areas than heavy snowfalls. But knowing wind conditions is not sufficient to predict these accumulations because their formations also depend on the snow quality of the snowpack surface upwind of the release zone. Consequently, assessment of snowdrift is required to improve avalanche forecasting. In accordance with this assumption, a new acoustic sensor was developed. The sensor includes a mechanical part designed to form a closed acoustic enclosure. The acoustic enclosure contains a microphone connected to an electrical amplifying and filtering device. Because the output information delivered by the instrument is proportional to the wind velocity and to the flux of solid particles (ice grains) drifted by the wind, the instrument is called an anémodriftometer. Prototypes of the instrument were first tested in a wind-tunnel and then at an experimental site in the Alps. Then an operational version, called Flow Capt, was developed and connected to the automatic weather station at 2700m in the Aminona ski resort (Switzerland). During the winter, snowdrift is recorded on the test site along with other meteorological parameters, and avalanche activity, to provide extensive on-site calibration and testing of the sensor. The experiment demonstrates that the instrument is a useful component of the avalanche forecasting chain
Keywords: acoustics, sensor, avalanche forecasting, snowdrift.
Keywords: acoustics, sensor, avalanche forecasting, snowdrift.
1. A new snowdrift sensor to improve avalanche forecasting
Wind can create even greater unstable accumulations of snow in mountainous areas than heavy snowfalls. But knowing wind conditions is not sufficient to predict these accumulations because their formations also depend on the snow quality of the snowpack surface all around measurement stations : at a given place, effective snowdrift will require high wind velocities, while for another snow pack snowdrift will already occur at low wind velocities. Knowing snowdrift by direct measurements is subsequently of high importance for avalanche forecasting (fig. 1).
Proc. DAGA 98, Fortschritte der Akustik, pp 144-
Acoustic Sensor To Measure Wind Velocity And
Snowdrift For Snow Avalanche Forecasting
Vincent CHRITIN, Thierry Melly
IAV Engineering -
PSE/A, EPFL -
Fax + 41 21 693 83 93 -
Fig. 1: Left - On the field, snowdrift is measured periodically by security patrollers, with the so-called Manual Driftometer. This simple instrument makes possible quantitative snowdrift assessments, but it requires the presence of a human observer on the sites. Compared to this method, the new acoustic sensor gives the possibility of continuous and automatic recording of snowdrift. Right - Typical snowdrift profile, From Föhn (1980).
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