後藤 健介

河川線形のフラクタル次元を求める際, 地図から求めることが多いが, 本研究では, 衛星リモートセンシングデータを用い, ボックスカウンティング法で河川線形のフラクタル次元を求めた.衛星数値データは, LANDSAT/MSS, LANDSAT/TM, SPOT/HRVの3種類を使用した.九州北部の河川を対象として, そのフラクタル次元を各衛星数値データから求めたものと2種類および3種類の衛星数値データを併用して求めたものとで比較した.また, 中国松花江で起きた洪水時の河川の変化をフラクタル次元を用いて比較した.得られた結論は次のとおりである.(1)対象とした河川のフラクタル次元は1.0に近い値であり, 河川線形はそれほど複雑でなかった.(2)それぞれの衛星数値データから求めたものと併用したものとで, フラクタル次元にほとんど差はなかった.(3)衛星数値データは河川線形のフラクタル次元の測定に有用である.(4)洪水氾濫による河川流域の拡大は, 衛星数値データを用いたフラクタル次元によって, これまでよりも適切に表現できる.

The aim of this study is to determine the optimum vegetation index for analysing damage due to a forest fire and to obtain a damage-degree map of the forest fire based on the optimum vegetation index, by using satellite remote sensing. The forest fire which occurred at Kuji City, Iwate Prefecture on April 27,1983 was treated, Landsat/MSS data before and after the forest fire were used, and six vegetation indices namely RVI, DVI1,DVI2,NDVI, TVI and GVI were compared in order to decide the optimum vegetation index. The F-test together with the t-test was carried out for the ratio of the individual vegetation index before and after the forest fire resulting in it that DVI2 was the optimum. Lastly the damage-degree map of the forest fire was obtained by the optimum DVI2 vegetation index, being very appropriate in comparison with in-situ survey and the air photo analysis.

The Typhoon 9119 attacked the northern part of Kyusyu District, the western part of Yamaguchi Prefecture and Hokkaido District on September 27 to 28,1991. This typhoon was so strong that considerable damages on cedars forests in Hita City, Oita Prefecture, apples orchards in Aomori Prefecture and others were yielded. One of its characteristics was a windy typhoon which triggered a lot of power failures due to salt damage in Chugoku District including Hiroshima, Yamaguchi and Okayama Prefectures. In this paper the authors analysed these power failures in Yamaguchi Prefecture by comparing two sets of the vegetation vigour data obtained from satellite remote sensing before and after the typhoon. The satellite data were MOS-1/MESSR data with the space resolution of 50 m and the vegetation vigour was calculated by RVI (Ratioed Vegetation Index). As a result the distribution map of salt damages examined by RVI almost coincided with that of salt-damage triggered power failures obtained by surveying in situ. Lastly the countermeasure against this kind of power failures was proposed with space and ground remote sensing technique.

As a result of the windy with little rain Typhoon 9713 which passed around the vicinity of Nansei Islands, Japan on August 18,1997,a lot of salt damages occurred on the sugar cane fields. In order to evaluate these damages the ground remote sensing technique together with the Landsat Satellite data were used. At first as of the in-situ investigation by using the ground remote sensing technique such as a portable photometer and a thermal infrared camera at Amami-Oshima Island it was cleared that the damages occurred on the sugar cane farms by the salt water can be easily observed. Secondly, through the analysis of the Landsat Stellite data it was found out that the damaged areas in Amami-Osima and Kikaishima islands can be detected by evaluating the normalized difference vegetation index (NDVI). Finally, based on these investigations the authors proposed that early detection with the ground remote sensing, the exact grasp of damaged areas using the satellite data and sprinkling with water sprinklers or vaccum cars are effective as the countermeasure against salt damages of suger cane fields.