定点カメラ画像による日々の積雪水当量図の作成(数値地形図の技術と応用)

元データ 2008-01-25

概要

The purpose of this study is to build daily raster maps of snow water equivalent in a mountain summit area from time marching images taken by a monitor camera placed at the foot of the Mt. Norikura, central Japan. The data sets of the hourly images are delivered by the Environment Ministry, Japan through the internet. Although the images have high resolution in time and space, but the projection axis is far from the vertical. We needed at first to get orthographic images from the original ones, which showed the daily march of snow covered areas. We used a 10m-DEM for the target area prepared by Hokkaido Map Co. Ltd. The DEM was utilized for the orthographic conversion mentioned above and also for getting topographic properties of each pixel and building daily raster maps of the daily mean temperature. The pixel temperature was estimated from the elevation in the DEM and calculated daily lapse rates between an observatory at the summit and surrounding stations of AMeDAS (Automated Meteorological Data Acquisition System). We interpolated daily images deficit because of rain or fog all day long. The intermediate image was got by marginal shrinking of snow cover area in the image and marginal expanding in the image of the next chance. Daily speed of shrinking and expanding were presumed to be distributed after the temperature of the day for cumulative temperature during the period. And checking all daily images during snow melt season we got a raster maps that indicated the date of snow disappearance for each pixel. Then we calculated the total cumulative temperature (degree-day) for each pixel from a specific date to the date of snow disappearance. Using the snow melting coefficient in the degree-day method, this map shows nothing short of water equivalent distribution on the specific day. In this way we could get information of each pixel not only on existence of snow but also water equivalent of snow. Using obtained images, we analyzed the seasonal march of snow melting quantitatively in relation to topographic properties, for example, altitude, degree and orientation of slopes and landforms of ridge or ravine. We could show effectiveness of the surface monitoring camera.

著者

森田 圭 日本大学大学院理工学研究科地理学専攻

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