Snow Survey with the Aerial Photograph in the Mountainous Region

Abstract

In order to measure the amount and distribution of snows in the experimental watershed, where the relation between changes in forest condition and runoff was being investigated, the snow survey by means of the aerial photograph was carried out at Takaragawa Experimental Forest (area : 20 km², altitude : 800-1945 m) in snowy district of Japan, in the winter of 1965-1966.
The depth of snow at the points corresponding to every intersection of grid overlaid with 100 meter interval on a map was measured as a difference of height between snow surface and ground surface, comparing vertical photographs of the watershed with snow and ones without snow. Mean depth and water equivalent of snow in the watershed, which were calculated using the said data along with the density of snows measured in on-the-spot survey, were about 3.4 meters and 1370 millimeters respectively at 1st of March.
The distribution of the accumulated snow in the mountainous region depends strogly on the topographic features, but the grade of influence of each topographic factor upon the distribution was varried according to the extent of examined area. Although the distribution of the depth of drifted snow at each point in the basin was complicate, the mean depth on a certain zone was expressed as a function of the topographic factor, such as altitude or distance from main mountain range.
It was shown in this experiment that the snow survey with the aerial photograph would be useful in analyzing the snow distribution in the mountaious watershed, though many problems remain to be solved in the future.