1998 年 18 巻 1 号 p. 42-56
The spectral properties of tree leaves throughout seasonal stages of ageing were measured using a spectrophotometer with an integrating sphere in the region of 350-2500nm. Changes occurring in the near-infrared region (760-910nm) were of most interest.
Results were obtained first from spectral measurements of a single leaf, and then from multiple leaves.
Spectral features of a single leaf with autumn senescence (yellow and red) showed significant change in the visible, and only slight change in the near-infrared. From the point of photosynthesis, vigor was lost in the autumn senescence leaf, hence, vigor of plants was not accessible with the reflectance of a single leaf in the near-infrared region. Leaf reflectance in the region increased as water was lost. This increase was due to leaf structure alteration as air voids increased inside. Spectral reflectance of a dead leaf in the near-infrared region showed "plateau rounding", whereas spectral reflectance of a live leaf in the near-infrared region showed "plateau".
Total reflectance of multiple stacked autumn senescence leaves (almost pure yellow and pure red) in the near-infrared region was high due to high transmittance in the region. Total reflectance of multiple stacked dead leaves in the near-infrared region was low due to low transmittance in the region. The relation of spectral properties between visible and near-infrared regions demonstrated that VI and NDVI were a virtual index of the vigor of vegetation. In order to discriminate ecosystem types with terrestrial vegetation by the spectral changes of seasonal stages of ageing using remote sensing techniques, algorithms utilizing visible bands should be introduced.