This study applied the MOD13Q1 VI product because the advantages in the ability to
monitor vegetation condition (Huete et al. 2002). This product was appropriate for
vegetation study at the regional scale in northeast Thailand in terms of spatial and temporal
resolution. The monthly VCI value corresponding to the sample sites was calculated from
the mean of selected 3 9 3 pixel (resolution 250 m per pixel) of each site covering area
about 0.5 km2
. From this step, the monthly VCI at all test sites from year 2001 to 2009 was
processed to analyze drought impact on vegetation at the different land cover type