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2. Principle of the FlowCapt anemo-driftometer
The FlowCapt anemo-driftometer determines both wind velocity and snow particles flux. The detection principle is based on mechanical-acoustical coupling. The sensor is composed of closed pipes containing electro-acoustic transducers and a powering, filtering and amplifying unit. When the sensor is placed into a snow particles flux, the particles shock the sensor pipes. inducing acoustical pressure. The pressure is picked-up by the transducers. The electrical outputs are filtered and time-averaged in given frequency ranges to provide a signal proportional to particles flux Q (kg m-2 s-1). The formal relation between the measured acoustic pressure and the snow particles flux Q requires the determination of the mechanical-acoustical coupling equations for the sensor, according to suitable hypothesis about particle impacts. The wind velocity is determined on a similar principle: the wind interacts with the body of the sensor and induces acoustic pressure into air enclosures. Suitable sensitivity can be obtained optimising the body shape and structure to the expected wind velocities.
3. Prototyping of the anemo-driftometer
Theoretical and experimental campaigns have been carried-out at the Swiss Federal Institute for Technology (EPFL) to develop FlowCapt prototypes (Fig. 2).
Fig. 2. Calibration with controlled particles flux on test-bench, at LEMA-EPFL (from Castelle, 1994)
Because snowdrift happens during windy periods, it is necessary that the sensor strongly discriminates wind from snowdrift. This property can be obtained by an appropriate design of the mechanical-acoustical coupling. With no mobile components and full-protected transducers (inside closed cavities), the FlowCapt is very suitable for stringent topographical and climatic environments.
Fig. 3. Measurement on bench-test of a controlled 8 m/s, 20-100 µm glass particles flux with FlowCapt (click on picture to see details)
Fig 4. Wind velocity comparative measurements, with reference MiniAir5™ propeller anemometer and FlowCapt prototype (click on picture to see details)
Results obtained from the validation experiments show linearity of the sensor vs. particles flux and wind speed (Figs. 3 and 4). On the basis of the obtained results, the industrial development of the FlowCapt began. A particular attention was paid on the calibration and reliability to ensure precise quantitative snowdrift information.
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The FlowCapt anemo-driftometer determines both wind velocity and snow particles flux
Tags:wind velocity, snow particles flux, flowcapt, snowdrit sensor
Cold Regions Science and Technology 30 (1999) 125—133
FlowCapt: a new acoustic sensor to measure
snowdrift and wind velocity for avalanche forecasting
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