2.2.1. Satellite data
The MODIS data (acquired in 2002) were provided by the EOS Data Gateway (EOS, 2004). The product name is “MODIS/Terra surface reflectance 8-day Global 500 m SIN GRID v004”. The product was composed so as to have the lowest value of band 3 over every 8 days (Vermote & Vermeulen, 1999). In addition, the product had already been systematically corrected for the effects of gaseous and aerosol scattering. Each pixel includes the ground reflectance ratio. Even with correction, the effects of the Bi-directional Reflectance Distribution Function (BRDF) on VI remained as noise. Time-series analysis is necessary in order to reduce the remaining noise. The observation date and sensor zenith angle of each pixel were accounted for in this study to cut out misleading data.