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Moderate Resolution Imaging Spectroradiometer (MODIS) continuously monitors gross primary production (GPP), which is an extremely important component of carbon cycling, at the global scale. Uncertainties about MODIS GPP limit our ability to accurately quantify GPP at the regional scales. The Collection 6 MODIS/Terra and MODIS/Aqua GPP products (i.e. MOD17A2H and MYD17A2H) were compared with the estimated GPP (GPPEC) by eddy covariance measurements in an alpine meadow in the Northern Tibetan Plateau during three consecutive growing seasons of 2005-2007. The Collection 6 MODIS/Terra and MODIS/Aqua fractional photosynthetically active radiation (FPAR) products (i.e. MOD15A2H and MYD15A2H) were also validated. The MOD17A2H and MYD17A2H products tended to overestimate GPPEC by 2.17% and 7.35% in 2005-2007, respectively, although these differences were not significant. The MOD15A2H and MYD15A2H products also tended to overestimate ground-based FPAR (FPARG) by 20.31% and 24.73% in 2005-2007, respectively. The overestimation of FPAR resulted in about 17.51-23.97% overestimation of GPPEC. The default maximum light-use efficiency (εmax) of 0.86 g C MJ-1 only underestimated the ground-based εmax (0.88 g C MJ-1) by 2.27%, which in turn resulted in about 2.13-2.72% underestimation of GPPEC. The meteorology data errors only caused about 0.48-1.06% underestimation of GPPEC. Therefore, although MODIS Collection 6 GPP had a very high accuracy, the input parameters had relative greater errors in the alpine meadow of the Northern Tibetan Plateau. The differences between MODIS GPP and GPPEC mainly resulted from FPAR, followed by εmax and meteorological data. [ABSTRACT FROM AUTHOR]

Large-scale atmospheric systems, such as the Southern Oscillation, North Atlantic Oscillation, and so on, are important climatic change indicators over the northern hemisphere. These systems play essential roles in regional-to-continental scale climate fluctuation and vegetation activity in response to global change. Using the Pathfinder AVHRR NDVI (Advanced Very High Resolution Radiometer Normalized Difference Vegetation Index) data for the period 1982-2000, the authors investigated the relationship of the inter-annual variations of spring NDVI to nine large-scale climate indices. On average, 57.2% of the satellite-sensed NDVI variance was explained. These climate indices also accounted for a large portion of the trends in NDVI as observed in five regions, namely, north-west North America (climate-related trend was 18.2%/10 years), south-eastern North America (5.8%/10 years), Europe (6.9% /10 years), high-latitude Asia (12.4%/10 years), and East Asia (8.0%/10 years). The results are useful for understanding and predicting the regional-to-continental NDVI variations in response to global climate change. [ABSTRACT FROM AUTHOR]