Avalanche!

Adam Abate, Hiroaki Katsuragi


I'm using diffuse light scattering technique (SVS, or Speckled Visibility Spectroscopy to be specific) to investigate dynamic properties of sand, especially avalanches. The basic idea behind the technique is that I can derive the fluctuation of the scatterers by observing the intensity variation of the scattered speckles across the pixels on a CCD camera. If the fluctuation of the scatteres is low during exposure of the CCD camera, then a speckled pattern of the scattered light across the CCD camera will remain distinct, whereas if the fluctuation of the scatterers is high during exposure of the CCD camera, the speckled pattern of the scattered light across the CCD camera will be averaged-out. Hence, slow fluctuation gives high "visibility" and fast fluctuation gives low "visibility." The idea is analogous to looking at a spinning wheel. When the wheel is spinning slowly, is is quite visible, whereas if the wheel is spinning fast, its details are washed-out.

With this new technique, I can get a time-dependent signal from the scatterers as fast as the CCD camera's exposure rate. I'm trying to see how sand fluctuates (its granular temperature) around the avalanche region.