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.