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, such as MODIS, CYCLOPES, and GLOBCARBON have been generated with different spatial and temporal resolutions from optical satellite sensors. However, to effectively use these LAI products in various disciplines, it is critical to get the knowledge of the quality of these products.

Prof. FANG Hongliang, Institute of Geographic Sciences and Natural Resources Research (IGSNRR) and his colleagues developed a new triple collocation error model (TCEM) to cross-validate the global products and produce consistent uncertainty information. Global monthly absolute and relative uncertainties, in 0.05° spatial resolutions, are generated for three major LAI products: MODIS, CYCLOPES, and GLOBCARBON. CYCLOPES shows the lowest absolute and relative uncertainties, followed by GLOBCARBON and MODIS. Grasses, crops, shrubs, and savannas usually generate lower uncertainties than forests because the latter has relatively larger LAI values. With their densely vegetated canopies, tropical regions exhibit the highest absolute uncertainties but the lowest relative uncertainties. The estimated uncertainties of CYCLOPES generally meet the accuracy requirements (±0.5) proposed by the Global Climate Observing System (GCOS), whereas for MODIS and GLOBCARBON only non-forest biome types have met the requirement. Nevertheless, no product seems to be within a relative uncertainty requirements of 20%. While further assessment of the uncertainty information is necessary, the present study provides an important benchmark in demonstrating the realization of the Stage 4 validation for global LAI products. The approach can be easily extended as a practicaltool for similar multi-product intercomparison and error estimation.

This work was supported by the Chinese Academy of Sciences.The studies have been published in the recent issue of Remote Sensing of Environment. The TCEM software package is available upon request to the corresponding author below.

For more information, contact

Hongliang FANG, Ph.D, Professor

LREIS, Institute of Geographic Sciences and Natural Resources Research

Chinese Academy of Sciences

11A Datun Road, Beijing, 100101, China

Tel: +86 10 6488 8005

Fax: +86 10 6488 9630

Email: fanghl@lreis.ac.cn

References:

Fang, H., S. Wei, C. Jiang, and K. Scipal, 2012. Theoretical uncertainty analysis of global MODIS, CYCLOPES and GLOBCARBON LAI products using a triple collocation method. Remote Sensing of Environment, 124, 610-621, doi: 10.1016/j.rse.2012.06.013.