Global assessment of Vegetation Index and Phenology Lab (VIP) and Global Inventory Modeling and Mapping Studies (GIMMS) version 3 products

Abstract

Earth observation based long-term global vegetation index products are used by scientists from a wide range of disciplines concerned with global change. Inter-comparison studies are commonly performed to keep the user community informed on the consistency and accuracy of such records as they evolve. In this study, we compared two new records: (1) Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index Version 3 (NDVI3g) and (2) Vegetation Index and Phenology Lab (VIP) Version 3 NDVI (NDVI3v) and Enhanced Vegetation Index 2 (EVI3v). We evaluated the two records via three experiments that addressed the primary use of such records in global change research: (1) prediction of the Leaf Area Index (LAI) used in light-use efficiency modeling, (2) estimation of vegetation climatology in Soil-Vegetation-Atmosphere Transfer models, and (3) trend analysis of the magnitude and phenology of vegetation productivity. Experiment one, unlike previous inter-comparison studies, was performed with a unique Landsat 30 m spatial resolution and in situ LAI database for major crop types on five continents. Overall, the two records showed a high level of agreement both in direction and magnitude on a monthly basis, though VIP values were higher and more variable and showed lower correlations and higher error with in situ LAI. The records were most consistent at northern latitudes during the primary growing season and southern latitudes and the tropics throughout much of the year, while the records were less consistent at northern latitudes during green-up and senescence and in the great deserts of the world throughout much of the year. The two records were also highly consistent in terms of trend direction/magnitude, showing a 30+ year increase (decrease) in NDVI over much of the globe (tropical rainforests). The two records were less consistent in terms of timing due to the poor correlation of the records during start and end of growing season.