2024 年 42 巻 p. 95-102
The propagation characteristics of sonic waves in snowpacks are important for internal structure exploration as well as the immediate rescue of people buried in snow avalanches. We buried a loudspeaker at the bottom of a snow pit and generated sonic waves of varying frequencies, primarily in the audible range; these waves were captured at the pit roof to examine sound propagation through the snowpack. The experiment was conducted in a pit with a disturbed snowpack to simulate an avalanche deposition with two average densities of 380 kg m−3 (loose fill) and 680 kg m−3 (dense fill). The results indicate that low-frequency (200-1000 Hz) waves are less attenuated than those at higher frequencies regardless of the snow density in the pit. Comparisons of sound propagation in loosely and densely filled snowpacks showed that sonic waves are less attenuated in densely filled snowpacks than in loosely filled snowpacks, especially at high frequencies (1.5-5.0-kHz band). The results of the acceleration spectral ratio and snow profile survey showed that sonic waves are amplified by multiple reflections in layers with a high physical property contrast. These facts suggest that sonic waves can be used to search for people buried in snow avalanches when the appropriate frequencies are selected depending on the diverse snowpack characteristics.
