where ρred and ρnir are reflectance of visible red and near-infrared, respectively. However, according to
the results of time-series ground observation of the spectral indices and seasonal changes of a forest
canopy, the conditions of the canopy in autumn indicated by NDVI are not identical among years;
therefore, it is difficult to monitor leaf autumn coloring by using time-series NDVI [13]. One simple
and possible reason for this problem is that NDVI is not sensitive enough to the leaf-color change from
green to yellow or red because green reflectance is not used in the calculation of NDVI. Meanwhile, there
are a lot of spectral bands which can be measured by using remote sensing. Therefore, it is important
to seek the applicability of various other spectral indices to develop the phenology detection with
remote sensing.