@article{oai:nipr.repo.nii.ac.jp:00010133,
 author = {Sugiura, Konosuke and Nagai, Shin and Nakai, Taro and Suzuki, Rikie and Sugiura, Konosuke and Nagai, Shin and Nakai, Taro and Suzuki, Rikie},
 issue = {2},
 journal = {Polar science, Polar science},
 month = {Jun},
 note = {Satellite remote sensing studies of snow cover in high-latitude boreal forests require ground-truth verification based on ground observation networks. In this study, we used time-lapse digital images to precisely detect the extent of snow cover at nine locations in the boreal forests of Alaska, and to demonstrate the relationship of these ground-truth measurements to satellite indices of snow cover. Our results show that normalized difference vegetation indices (NDVIs) and normalized difference water indices (NDWIs) show significant variations at the end and beginning periods of continuous snow cover: the NDVIs on the last days of continuous snow cover ranged from 0.12 to 0.37, and those on the first days of continuous snow cover ranged from 0.16 to 0.38. The normalized difference snow indices (NDSIs) were also positive during periods of continuous snow cover and negative during periods of no snow cover. The NDWIs varied significantly from the beginning to the end of periods of continuous snow cover. This study confirms that continuous snow cover is important for accurate phenological studies using NDVIs in the region of the trans-Alaska camera network. Simple cameras can be effectively utilized in ground-based networks, functioning not only as a ground-truth verification tools for calibrating satellite indices, but also as a source of data to fill data gaps in satellite records., 北方林の積雪に関する衛星観測研究では、地上観測にもとづくグランドトゥース検証が必要である。本研究では、インターバルカメラをアラスカ北方林に９地点設置して北方林積雪の分布を詳細に検出し、積雪に関する衛星指標との関係を調べた。その結果、NDVI（正規化植生指数）、NDWI（正規化水指数）、NDSI（正規化積雪指数）に関して、根雪の前後における顕著な変化を捉えることができた（根雪の終わりのNDVIは0.12から0.37、根雪の始まりには0.16から0.38。NDSIは、積雪の有無により明瞭に変化し、積雪期には正の値、無雪期には負の値。NDWIは根雪の始まりから終わりまで著しく変動）。本研究により、積雪はアラスカ北方林でのNDVIを用いた正確なフェノロジー研究にとって重要であることが確認された。設置した簡易カメラは衛星指標の検証のための地上観測ツールとしてだけではなく、衛星観測の欠測期間を補うためのデータ源としても有効に機能した。},
 pages = {149--161},
 title = {Application of time-lapse digital imagery for ground-truth verification of satellite indices in the boreal forests of Alaska},
 volume = {7},
 year = {2013}
}