積雪中の音速
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概要
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The velocities of sound in the snow layers were measured to know the dynamical properties of them and to classify them by the velocity of sound in them. Two methods were employed to measure the sound velocities.<BR>The first method was performed in the field. Two microphones were laid in the snow layer. When the sound of explosion propergated from one microphone to the other, the time when the wave front reached the microphone_were measured with the electromagnetic oscillograph.<BR>The next method was performed in the laboratory. A block of the snow layer was taken in the long tube and the continuous sound of sine wave form were sent in the tube. Two microphones which were in the tube connected with the Brown tube oscillograph, one was vertically the other was horizontally, and Lissajous figures were obtained. When the frequency of sound were varied continuously the Lissajous figure became straight line. From this frequency the time of propergation were calculated and then the velocities of sound were calculated.<BR>There are three paths of sound from A which is a point on the vertical section of the snow layer to B which is a point in the snow layer (cf. Fig. 1) The first path is in the snow layer only. In this case the velocity of sound is about 190-250 m/sec. The second path is in air at the first and in the snow layer near the point B. The path in air must have at least one reflection, so that the apparent time of ropergation is longer than that of the minimum path which is assumed to have no reflection. The third path is in the layer of ice crust under the snow layer at the first. The apparent velocity of sound is about 700-1000 m/sec.<BR>The sound velocity was measured about the various snow layers with the second method and the results are as follows.<BR>a. The larger the density, the smaller the velocity.<BR>b. The larger the snow particle, the greater the velocity for the snow layer of same density.<BR>c. For the settled snow, when the snow is warmed and wetted, the velocity increases a little.<BR>But for the firn snow, these effects are not seen.
- 社団法人 日本雪氷学会の論文