Harmonization of Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) from Sea-ViewingWide Field-of-View Sensor (SeaWiFS) and Medium Resolution Imaging Spectrometer Instrument (MERIS)

Ceccherini, Guido; Gobron, Nadine; Robustelli, Monica

doi:10.3390/rs5073357

Cited by 6 publications

(6 citation statements)

References 28 publications

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“…fAPAR is a dimensionless variable, varying between zero and one, and is related to the state and change of vegetation amount and productivity. The authors of [27] note that due to the requirement for consistent radiometric processing, it is difficult to generate long time series of fAPAR estimates due to inconsistencies between sensors and drifts in calibration of single sensors over time. In this study, it is produced in a step subsequent to the LAI retrieval procedure.…”

Section: Fapar: Fraction Of Absorbed Photosynthetically Active Radiationmentioning

confidence: 99%

A New Global fAPAR and LAI Dataset Derived from Optimal Albedo Estimates: Comparison with MODIS Products

et al. 2016

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We present the first comparison between new fAPAR and LAI products derived from the GlobAlbedo dataset and the widely-used MODIS fAPAR and LAI products. The GlobAlbedo-derived products are produced using a 1D two-stream radiative transfer (RT) scheme designed explicitly for global parameter retrieval from albedo, with consistency between RT model assumptions and observations, as well as with typical large-scale land surface model RT schemes. The approach does not require biome-specific structural assumptions (e.g., cover, clumping, understory), unlike more detailed 3D RT model approaches. GlobAlbedo-derived values of fAPAR and LAI are compared with MODIS values over 2002-2011 at multiple flux tower sites within selected biomes, over 1200ˆ1200 km regions and globally. GlobAlbedo-derived fAPAR and LAI values are temporally more stable than the MODIS values due to the smoothness of the underlying albedo, derived via optimal estimation (assimilation) using an a priori estimate of albedo derived from an albedo "climatology" (composited multi-year albedo observations). Parameters agree closely in timing but with GlobAlbedo values consistently lower than MODIS, particularly for LAI. Larger differences occur in winter (when values are lower) and in the Southern hemisphere. Globally, we find that: GlobAlbedo-derived fAPAR is~0.9-1.01ˆMODIS fAPAR with an intercept of~0.03; GlobAlbedo-derived LAI is~0.6ˆMODIS LAI with an intercept of~0.2. Differences arise due to the RT model assumptions underlying the products, meaning care is required in interpreting either set of values, particularly when comparing to fine-scale ground-based estimates. We present global transformations between GlobAlbedo-derived and MODIS products.

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Section: Fapar: Fraction Of Absorbed Photosynthetically Active Radiationmentioning

confidence: 99%

A New Global fAPAR and LAI Dataset Derived from Optimal Albedo Estimates: Comparison with MODIS Products

et al. 2016

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“…ATSR, MERIS, MISR, MODIS, SEVIRI, SeaWiFS, VEGETATION) at different spatial and temporal resolutions. Although there have been substantial efforts to harmonise products across sensors (Ceccherini et al, 2013) and establish standards and validation practices (e.g. Widlowski, 2010), there are still considerable differences among the products.…”

Section: Reflectance-based Vegetation Dynamics/activitymentioning

confidence: 99%

Reviews and syntheses: Systematic Earth observations for use in terrestrial carbon cycle data assimilation systems

et al. 2017

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Abstract. The global carbon cycle is an important component of the Earth system and it interacts with the hydrology, energy and nutrient cycles as well as ecosystem dynamics. A better understanding of the global carbon cycle is required for improved projections of climate change including corresponding changes in water and food resources and for the verification of measures to reduce anthropogenic greenhouse gas emissions. An improved understanding of the carbon cycle can be achieved by data assimilation systems, which integrate observations relevant to the carbon cycle into coupled carbon, water, energy and nutrient models. Hence, the ingredients for such systems are a carbon cycle model, an algorithm for the assimilation and systematic and well errorcharacterised observations relevant to the carbon cycle. Relevant observations for assimilation include various in situ measurements in the atmosphere (e.g. concentrations of CO 2 and other gases) and on land (e.g. fluxes of carbon water and energy, carbon stocks) as well as remote sensing observations (e.g. atmospheric composition, vegetation and surface properties).We briefly review the different existing data assimilation techniques and contrast them to model benchmarking and evaluation efforts (which also rely on observations). A common requirement for all assimilation techniques is a full description of the observational data properties. Uncertainty estimates of the observations are as important as the observations themselves because they similarly determine the outcome of such assimilation systems. Hence, this article reviews the requirements of data assimilation systems on observations and provides a non-exhaustive overview of current observations and their uncertainties for use in terrestrial carbon cycle data assimilation. We report on progress since the review of model-data synthesis in terrestrial carbon observations by Raupach et al. (2005), emphasising the rapid advance in relevant space-based observations.

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“…This led to the generation of multiple datasets, stimulated the organization of field campaigns to acquire in situ measurements, and prompted CEOS to address discrepancies in the context of its calibration and validation working group. Efforts to harmonize FAPAR datasets are ongoing (e.g., Ceccherini et al 2013). Yet, despite intense research and sustained efforts to establish standards and best practices (e.g., on validation; Widlowski 2010), no institution has proposed to be or been identified to serve as the central point of contact for the worldwide compilation, archiving, and distribution of FAPAR datasets.…”

Section: Discussion and Illustrationmentioning

confidence: 99%

The Concept of Essential Climate Variables in Support of Climate Research, Applications, and Policy

Bojinski

Verstraete

Peterson

et al. 2014

Bulletin of the American Meteorological Society

769

481

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Harmonization of Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) from Sea-ViewingWide Field-of-View Sensor (SeaWiFS) and Medium Resolution Imaging Spectrometer Instrument (MERIS)

Cited by 6 publications

References 28 publications

A New Global fAPAR and LAI Dataset Derived from Optimal Albedo Estimates: Comparison with MODIS Products

A New Global fAPAR and LAI Dataset Derived from Optimal Albedo Estimates: Comparison with MODIS Products

Reviews and syntheses: Systematic Earth observations for use in terrestrial carbon cycle data assimilation systems

The Concept of Essential Climate Variables in Support of Climate Research, Applications, and Policy

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