Item: Particle image velocimetry; a new technique to measure strain in loaded snow
Title: Particle image velocimetry; a new technique to measure strain in loaded snow
Proceedings: Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming
Authors: J. Andrew Gleason, Colorado Avalanche Information Center and University of Wyoming
Abstract: A new technique has been developed to accurately measure strain in snow subjected to a band load. While stress beneath loaded snow has been measured, accurate measurements of strain have only been evaluated posthumous to the application of the load. A 0.156 m3 sample of snow was placed into an aluminum cube with a clear lexan side and loaded from above with a 0.025 m2 band load. The displacement caused by the loading was calculated using particle image velocimetry (PIV) in which particle paths are traced with a rapid sequence of digital photographs. This technique utilizes a method of non-intrusive velocity measurements designed for the measurement of flow velocities in fluids. The medium must be seeded with tracer particles in order for the software to follow the reflected light of each tracer particle as it moves under a band load. A digital camera is used to capture one plane of displacement transverse to the band load through the clear lexan wall. A sequence of digital images is collected while the snow is loaded from above. The PIV post-processing software is able to follow individual tracer particles both spatially and temporally. The output from the PIV software generates a vector field that allows conversion of displacement to a strain field. Various experiments were conducted with layers of different density, crystal type and resistance (hardness) of snow. The strain fields show a distribution of the band load that varies with snow surface layer density and resistance. Strain is shown to concentrate at snow layer boundaries.
Keywords: snow strain, particle image velocimetry, snow load
Digital Abstract Not Available