FlowCapt: a new acoustic sensor to measure snowdrift and wind velocity foravalanche forecasting

Wind can create even greater unstable accumulations of snow in mountainous areas than heavy snowfalls. But knowing wind conditions is not sufficient t o predict these accumulations because their formations also depend on the s now quality of the snowpack surface upwind of the release zone. Consequentl y, 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 enclos ure. The acoustic enclosure contains microphones 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 s olid particles (ice grains) drifted by the wind, the instrument is called a n anemo-driftometer, Prototypes of the instrument were first tested in a wi nd tunnel and then at an experimental site in the Alps. Then an operational version, called FlowCapt, was developed and connected to an automatic weat her station at 2700 m in the Aminona ski resort (Switzerland). During the w inter, snowdrift is recorded on the test site along with other meteorologic al parameters, and avalanche activity, to provide extensive on-site calibra tion and testing of the sensor. The experiment demonstrates that the instru ment is a useful component of the avalanche forecasting chain. (C) 1999 Els evier Science B.V. All rights reserved.