Leaf Area Index (LAI) indicates the amount of live green leaf above ground surface. Many agro-meteorology, atmospheric general circulation, and biogeochemical models rely on LAI to parameterize the vegetation interactions with the atmosphere. A series of LAI products have been generated from different satellite data. However, to effectively use these LAI products in various disciplines, it is important to know how these products perform.

Prof. FANG Hongliang, Institute of Geographic Sciences and Natural Resources Research (IGSNRR), together with several European and American scientists, developed a benchmark to compare five major global LAI products: MODIS, GEOV1, GLASS, GLOBMAP, and JRC-TIP. 

Their study shows that these products are generally consistent with each other, but have larger deviations for forest regions. Accordingly, they developed several equations to convert different products for different land cover types. They also found that MODIS product has the smallest uncertainties, followed by GEOV1, Land-SAF, and JRC-TIP. Generally, more than 75% data of these products could meet the accuracy requirements (±0.5) proposed by the Global Climate Observing System (GCOS). Nevertheless, they also revealed that large relative uncertainties appear in ecological transition zones in all of these products. 

Researchers concluded that inter-products discrepancies are mainly due to differences between definitions, retrieval algorithms, and input data. Prof. Fang suggested that future product development and validation studies should focus on areas (e.g., sparsely vegetated and savanna areas) and periods (e.g., winter time) with higher uncertainties.

Their work was supported by the Chinese Academy of Sciences and the National Natural Science Foundation of China. The studies have been published in the recent issue of Journal of Geophysical Research-Biogeosciences.

Fang, H., et al. (2013), Characterization and intercomparison of global moderate resolution leaf area index (LAI) products: Analysis of climatologies and theoretical uncertainties. J. Geophys. Res. Biogeosci., 118, doi:10.1002/jgrg.20051.