Journal ArticleDOI
MODIS leaf area index products: from validation to algorithm improvement
Wenze Yang,Bin Tan,Dong Huang,Miina Rautiainen,N.V. Shabanov,Yulei Wang,Jeffrey L. Privette,Karl F. Huemmrich,Rasmus Fensholt,Inge Sandholt,Marie Weiss,Douglas E. Ahl,Stith T. Gower,Ramakrishna R. Nemani,Yuri Knyazikhin,Ranga B. Myneni +15 more
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TLDR
This paper summarizes the experience of several collaborating investigators on validation of MODIS LAI products and suggests three key factors that influence the accuracy of LAI retrievals that are suggested from the model used to build the look-up tables accompanying the algorithm.Abstract:
Global products of vegetation green Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) are being operationally produced from Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) at 1-km resolution and eight-day frequency. This paper summarizes the experience of several collaborating investigators on validation of MODIS LAI products and demonstrates the close connection between product validation and algorithm refinement activities. The validation of moderate resolution LAI products includes three steps: 1) field sampling representative of LAI spatial distribution and dynamic range within each major land cover type at the validation site; 2) development of a transfer function between field LAI measurements and high resolution satellite data to generate a reference LAI map over an extended area; and 3) comparison of MODIS LAI with aggregated reference LAI map at patch (multipixel) scale in view of geo-location and pixel shift uncertainties. The MODIS LAI validation experiences, summarized here, suggest three key factors that influence the accuracy of LAI retrievals: 1) uncertainties in input land cover data, 2) uncertainties in input surface reflectances, and 3) uncertainties from the model used to build the look-up tables accompanying the algorithm. This strategy of validation efforts guiding algorithm refinements has led to progressively more accurate LAI products from the MODIS sensors aboard NASA's Terra and Aqua platformsread more
Citations
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Journal ArticleDOI
Improvements to a MODIS global terrestrial evapotranspiration algorithm
TL;DR: In this article, an improved version of the global evapotranspiration (ET) algorithm based on MODIS and global meteorology data has been proposed, which simplifies the calculation of vegetation cover fraction, calculating ET as the sum of daytime and nighttime components, adding soil heat flux calculation, improving estimates of stomatal conductance, aerodynamic resistance and boundary layer resistance, separating dry canopy surface from the wet and dividing soil surface into saturated wet surface and moist surface.
Journal ArticleDOI
Global Data Sets of Vegetation Leaf Area Index (LAI)3g and Fraction of Photosynthetically Active Radiation (FPAR)3g Derived from Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI3g) for the Period 1981 to 2011
Zaichun Zhu,Jian Bi,Yaozhong Pan,Sanmay Ganguly,Alessandro Anav,Liang Xu,Arindam Samanta,Shilong Piao,Ramakrishna R. Nemani,Ranga B. Myneni +9 more
TL;DR: Long-term global data sets of vegetation Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) are critical to understanding vegetation photosynthesis and its role in climate change.
Journal ArticleDOI
Evaluating the Land and Ocean Components of the Global Carbon Cycle in the CMIP5 Earth System Models
Alessandro Anav,Pierre Friedlingstein,M. Kidston,Laurent Bopp,Philippe Ciais,Peter M. Cox,C. D. Jones,Martin Jung,Ranga B. Myneni,Zaichun Zhu +9 more
TL;DR: In this paper, the authors assess the ability of 18 Earth system models to simulate the land and ocean carbon cycle for the present climate and find that the models correctly reproduce the main climatic variables controlling the spatial and temporal characteristics of the carbon cycle.
Journal ArticleDOI
Large seasonal swings in leaf area of Amazon rainforests
Ranga B. Myneni,Wenze Yang,Wenze Yang,Ramakrishna R. Nemani,Alfredo Huete,Robert E. Dickinson,Yuri Knyazikhin,Kamel Didan,Rong Fu,Robinson I. Negrón Juárez,S. S. Saatchi,Hirofumi Hashimoto,Kazuhito Ichii,N.V. Shabanov,Bin Tan,P. Ratana,Jeffrey L. Privette,Jeffrey L. Privette,Jeffrey T. Morisette,Eric Vermote,Eric Vermote,David P. Roy,Robert E. Wolfe,Mark A. Friedl,Steven W. Running,Petr Votava,Nazmi El-Saleous,Sadashiva Devadiga,Yin Su,Vincent V. Salomonson +29 more
TL;DR: There are reported seasonal swings in green leaf area of ≈25% in a majority of the Amazon rainforests, which may be critical to initiation of the transition from dry to wet season, seasonal carbon balance between photosynthesis gains and respiratory losses, and litterfall nutrient cycling in moist tropical forests.
Journal ArticleDOI
Validation and intercomparison of global Leaf Area Index products derived from remote sensing data
Sébastien Garrigues,Roselyne Lacaze,Frédéric Baret,Jeffrey T. Morisette,Marie Weiss,Jaime Nickeson,Richard Fernandes,S. Plummer,N.V. Shabanov,Ranga B. Myneni,Yuri Knyazikhin,Wenze Yang +11 more
TL;DR: In this paper, the performance of four major global leaf area index (LAI) products at 1/11.2° spatial sampling and a monthly time step was investigated. And the results showed that the CAI values agree better over croplands and grasslands than over forests.
References
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Journal ArticleDOI
Second Simulation of the Satellite Signal in the Solar Spectrum, 6S: an overview
TL;DR: The 6S code has still limitations; it cannot handle spherical atmosphere and as a result, it cannot be used for limb observations, and the decoupling the authors are using for absorption and scattering effects does not allow to use the code in presence of strong absorption bands.
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Review of methods for in situ leaf area index determination Part I. Theories, sensors and hemispherical photography
TL;DR: It is suggested that the use of a digital camera with high dynamic range has the potential to overcome a number of described technical problems related to indirect LAI estimation.
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Review of methods for in situ leaf area index (LAI) determination: Part II. Estimation of LAI, errors and sampling
TL;DR: In this paper, the theoretical background of modeling the gap fraction and the leaf inclination distribution is presented and different techniques used to derive leaf area index (LAI) and leaf inclination angle from gap fraction measurements are reviewed.
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Leaf area index of boreal forests: theory, techniques, and measurements
TL;DR: In this article, the authors evaluate the results obtained by several research teams using different methods for a broad spectrum of boreal forest types in support of the international Boreal Ecosystem-Atmosphere Study (BOREAS).