Ecophysiological consideration on the satellite-based vegetation index
2008
Nagai, S.(Gifu Univ. (Japan). River Basin Research Center) | Nasahara, K.N. | Ishihara, M. | Muraoka, H.
In order to evaluate the dates of bud-burst and leaf defoliation by using the satellite-based Normalized Difference Vegetation Index (NDVI), we need to identify that a certain value of the satellite-based NDVI showed the same phenological stage for every year. In the present study, we estimated the dates of bud-burst and leaf defoliation from 2004 to 2006 in a cool-temperate deciduous broad-leaved forest by using the ground-based NDVI, which was observed by the spectroradiometer situated above the canopy, and the satellite-based NDVI, which was obtained by the MODIS (Moderate Resolutioh Imaging Spectroradiometer) sensors onboard Terra and Aqua satellites. Then we confirmed thus estimated dates of bud-burst and leaf defoliation with the canopy photographs taken in the forest. The canopy photographs taken on the estimated dates of bud-burst and leaf defoliation showed the similar phenological status of the forest canopy for every year. This means that a certain value of NDVI may indicate the similar phenological stages for every year. The ground- and the satellite-based NDVIs increased in the bud-burst period and decreased in the leaf defoliation period. However, when we estimated the dates of bud-burst and leaf defoliation by using the threshold value, which was the midpoint between the annual maximum NDVI and the annual minimum NDVI, the estimated date of bud-burst was 20 days earlier than the ground observation and the estimated date of leaf defoliation was 32 days later than the ground observation.
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