Abstract
A new type of snow layer sonde was designed for the detection of layers in a snow cover. A pair of optical fibers are set up together at the end of a prove with a position sensor. The sonde rays constantly in contact with the snow from one of the two optical fibers, and it detects the light of diffuse reflection by the other optical fiber. The diameter of the optical fibers is 0.5mm. Modulation light is used in this sonde, and the wavelength is 660nm.
From field tests, it was found that settled snow has larger reflectivities than granular snow. The reflectivity is the percentage of the total intensity of reflected rays to incident rays. The boundary of the reflectivity between settled snow and granular snow was 1.0-1.6% for 280-370kg/m3 in density.
The reflectivities of granular snow showed a wider range than those of settled snow. The granular snow, in which strong reflection lights appeared, had grain sizes smaller than 1 mm in diameter. From the penetrating test of the sonde in glass beads of various sizes, it was proved that the reflection rays are condensed by a particle in the case of similar grain size (diameter: 0.5-1 mm) with a distance of 0.5mm between the centers of the two optical fibers. Therefore, the same phenomenon would occur in the granular snow layer as the glass beads.
