Inconsistent NDVI trends from AVHRR, MODIS, and SPOT sensors in the Tibetan Plateau

The Normalized Difference Vegetation Index (NDVI) from the National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA - AVHRR), Moderate Resolution Imaging Spectroradiometer (MODIS), and Systèm Pour l´Observation de la Terre-VEGETATION (SPOT-VEG) have been widely used in numerous local to global scale modeling and analysis. In this study, we evaluated the accuracy of the GIMMS NDVI and examined the potential errors of the NDVI data in the Tibetan Plateau. We found that the spring AVHRR NDVI decreased from late of 1990s, while SPOT and MODIS NDVI slightly increased during the same period. The AVHRR NDVI exhibit both a negatively and significantly correlation with water vapor (or precipitable water), suggesting AVHRR NDVI was affected by the atmospheric water vapor variation.