Blast noise propagation above a snow cover

A porous medium model of a snow cover, rather than a viscoelastic treatment , has been used to simulate measured, horizontally traveling acoustic wavef orm propagation above a dry snow cover 11-20 cm thick. The waveforms were p roduced by explosions of l-kg charges at propagation distances of 100 to 14 00 m. These waveforms, with a peak frequency around 30 Hz, show pulse broad ening effects similar to those previously seen for higher-frequency waves o ver shorter propagation distances. A rigid-ice-frame porous medium (''rigid -porous'') impedance model, which includes the effect of the pores within t he snow but ignores any induced motion of the ice particles, is shown to pr oduce much better agreement with the measured waveforms compared with a vis coelastic solid treatment of the snow cover. From the acoustic waveform mod eling, the predicted average snow cover depth of 18 cm and effective flow r esistivities of 16-31 kPa s m(-2) agree with snow pit observations and with previous acoustic measurements over snow. For propagation in the upwind di rection, the pulse broadening caused by the snow cover interaction is lesse ned, but the overall amplitude decay is greater because of refraction of th e blast waves. (C) 2001 Acoustical Society of America.