Analysis of the MISR LAI/FPAR product for spatial and temporal coverage, accuracy and consistency Jiannan Hu a , Yin Su a , Bin Tan a , Dong Huang a , Wenze Yang a , Mitchell Schull a , Michael A. Bull b , John V. Martonchik b , David J. Diner b , Yuri Knyazikhin a, ⁎ , Ranga B. Myneni a a Department of Geography, Boston University, 675 Commonwealth Avenue, Boston, MA 02215, USA b Jet Propulsion Laboratory, Pasadena, CA 91109, USA Received 1 March 2006; received in revised form 8 June 2006; accepted 16 June 2006 Abstract The Multi-angle Imaging SpectroRadiometer (MISR) instrument provides global imagery at nine discrete viewing angles and four visible/near- infrared spectral bands. MISR standard products include green leaf area index (LAI) of vegetation and fraction of photosynthetically active radiation absorbed by vegetation (FPAR). This paper describes the research basis for transitioning the MISR LAI/FPAR products from provisional to validation status. The efforts included not only comparisons to field data but also analyses of relationships, consistency and complementarity between various MISR products derived by independent algorithms. For example, we show how the energy absorbed by the ground below vegetation can be estimated from two independent MISR products, FPAR and BHRPAR (bi-hemispheric reflectance at PAR wavelengths). Further, we show that this information can be used to derive at least three measures of canopy structure — Beer's law extinction coefficient, mean leaf inclination and the gap fraction or vegetation ground cover. The spatial and temporal coverage of the LAI/FPAR product is mainly limited by cloud contamination. However, when a successful aerosol retrieval is performed, typically 95% of pixels have surface reflectance retrievals suitable as input to the LAI/FPAR algorithm. The algorithm provides LAI/FPAR retrievals in 50–80% of these pixels with suitable input. The early versions of the algorithm overestimated LAI values in grasses and broadleaf crops. The MISR LAI product from the recalibrated algorithm (version 3.3) is assessed by comparison with field data collected in a 3×3 km agricultural area (grasses and cereal crops) near Avignon, France. LAI retrievals in other biomes are compared to MODIS LAI product of known accuracy. The MISR LAI product shows structural and phenological variability in agreement with data. Our results suggest that the product is accurate to within 0.66 LAI in herbaceous vegetation and savannas and is an overestimate by about 1 LAI in broadleaf forests. LAI retrievals over needle leaf forests remain at provisional quality level. © 2006 Elsevier Inc. All rights reserved. Keywords: MISR; Leaf area index; Fraction of photosynthetically active radiation absorved by vegetation; Satellite product 1. Introduction The multi-angle imaging spectroradiometer (MISR) instru- ment is designed to provide global imagery at nine discrete viewing angles and four visible/near-infrared spectral bands. The MISR team is responsible for development and validation of algorithms and for producing a series of products which include vegetation green Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation (400–700 nm) absorbed by vegetation (FPAR). These products are required to describe the exchange of fluxes of energy, mass (e.g., water and CO 2 ) and momentum between the surface and atmosphere (Sellers et al., 1997). MISR LAI/FPAR research has three major components — algorithm development, product analysis and validation. Algo- rithm development includes the development of the at-launch algorithm (Knyazikhin et al., 1998a,b), prototyping of the algo- rithm prior to the launch of Terra platform (Zhang et al., 2000), and algorithm refinement (Hu et al., 2003). Product analysis includes assessment of the overall algorithm performance at global scale and assessment of the accuracy and quality of the product at regional scales with emphasis on understanding how input data uncertainties impact retrieval quality (Wang et al., 2001; Hu et al., 2003). Remote Sensing of Environment 107 (2007) 334 – 347 www.elsevier.com/locate/rse ⁎ Corresponding author. Tel.: +1 617 353 8843; fax: +1 617 353 8399. E-mail address: jknjazi@bu.edu (Y. Knyazikhin). 0034-4257/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.rse.2006.06.020