Microstructure and sound absorption of snow

Sound absorption of snow was measured for test specimens with porosities in the range from 46% to approximately 90% in an impedance tube at frequencies between 125 Hz and 1.6 kHz. In addition, the geometrical structure of the same samples was determined by X-ray microtomography. This novel experimental combination is to provide a reliable basis for the development of quantitative correlations between sound absorption and structure. The homogeneity of the samples was assessed by image analysis. Using the ‘simplified’ relaxation model of Wilson the measured sound absorption could be satisfactorily reproduced. Two of the four parameters of the absorption model were obtained directly, i.e. without fitting, from geometric quantities (porosity and surface density), while the other two parameters were determined by adaptation to the absorption. The air permeability deduced from the model parameters compares well with known measured and calculated values.

► Measurement of sound absorption of various snow samples.
► Micro-tomographic imaging of the same samples.
► First experimental basis for relating acoustic properties and micro-structure ab initio.
► Successful reproduction of measured sound absorption by Wilson's relaxation model.
► Prospects of acoustical determination of permeability of snow.