Estimation of canopy openness with hemispherical photographs : Supervised classification of colour image

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  • 全天空写真による樹冠開空度の推定 : カラー画像の教師付き分類
  • ゼン テンクウ シャシン ニ ヨル ジュカン カイクウド ノ スイテイ カラー ガゾウ ノ キョウシ ツキ ブンルイ

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Abstract

We examined the effects of the following three conditions on estimating canopy openness with colour hemispherical photographs : the distance between exposure sites, resolution of scanning film and zenith angle of cutting hemispherical photographs. First, four plots were established in broad-leaved natural forests dominated by beech (Fagus crenata BLUME) and color pictures of the canopy were taken with a fish eye lens there. Next, the photographs were scanned with a film scanner and the images were separated into sky and canopy by supervised classification. Moreover, canopy openness was estimated under various conditions for each plot and errors of estimates were calculated from standard errors of averages. In conclusion, the distance had little to do with canopy openess ; the resolution under 680dpi decreased the error, although the error was almost constant over 680dpi ; the zenith angle did not affect canopy openness.

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