1. 1) B. Jamieson and T. Geldsetzer, Avalanche Accidents in Canada (Canadian Avalanche Association, Revelstoke, B.C., 1996).
2. 2) R. Nitta, From the World of Avalanche (Nadare no Sekai kara), (Kokon Shoin, Tokyo, 2000) (in Japanese).
3. 3) T. Ishida and S. Onodera, "Sound absorption by snow layer," Low Temp. Sci., Ser. A, Phys. Sci., 12, 17–24 (1954) (in Japanese with English abstract).
4. 4) T. Ishida, "Acoustic characteristics of snow layer," Low Temp. Sci., Ser. A, Phys. Sci., 12, 59–72 (1964) (in Japanese with English abstract).
5. 5) T. Ishida, "Acoustic properties of snow," Contrib. Inst. Low Temp. Sci., A20, 23–63 (1965).