Abstract
Abstract Normalized Difference Vegetation Index (NDVI) in Global Vegetation Index (GVI) products from AVHRR which are provided by NOAA has been founded useful for global land cover monitoring. Though NDVI was designed to eliminate an effect of the change of solar illumination, there are some problems which still have to be removed, such as effects of the solar zenith angle, sampling method of GVI pixels, AVHRR channel degradation, scan angle, atmospheric condition and cloud contamination. In this paper, all factors are described with the emphasis on the effect of solar zenith angle. The effect of solar zenith angle on NDVI was simulated by LOWTRAN 7. The change of solar zenith angle by the delay of equator crossing local time and scan angle was clarified. Furthermore it is indicated that effects of the above factors on temporal variation of weekly NDVI data can be divided into low frequency variation and high frequency variation.
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