NOAA AVHRR weekly NDVI data from 1996
to 1998 and the year 2000 were obtained from the German
Remote Sensing Data Center (DFD). SPOT VEGETA-TION NDVI (1998–2001) were downloaded from the free
VEGETATION products site (http://www.free.vgt.vito.be/),
and 2001 Terra MODIS NDVI and enhanced vegetation
index (EVI) from the Earth Observing System Data
Gateway (EOS,http://www.edcimswww.cr.usgs.gov/pub/
imswelcome/). A weighted Fourier transform was applied
to simulate the NDVI time-course within the year (Sellers
et al., 1994).