Uncertainty estimates for the FAPAR operational products derived from MERIS — Impact of top-of-atmosphere radiance uncertainties and validation with field data

Gobron, Nadine; Pinty, B.; Aussedat, Ophélie; Taberner, Malcolm; Olga, Faber; Mélin, Frédéric; Lee, Thomas; Robustelli, Monica; Snoeij, P.

doi:10.1016/j.rse.2007.09.011

Cited by 65 publications

(55 citation statements)

References 35 publications

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“…We used an ensemble of 25 model trees to define a median best-estimate and uncertainty based on the spread of the estimates among the individual trees in the ensemble 4 . We used a harmonized FAPAR product from three sensors (AVHRR 25 , SeaWiFS 24 , MERIS 26 ), a remote-sensing-based global land-use map 27 , and observation-based products of climate variables 28,29 as forcing data. We estimated significance levels of trends on the basis of Mann-Kendall tests.…”

Section: Methods Summarymentioning

confidence: 99%

Recent decline in the global land evapotranspiration trend due to limited moisture supply

Jung

Reichstein

Ciais

et al. 2010

Nature

1,880

1,462

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More than half of the solar energy absorbed by land surfaces is currently used to evaporate water(1). Climate change is expected to intensify the hydrological cycle(2) and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land-a key diagnostic criterion of the effects of climate change and variability-remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network(3), meteorological and remote-sensing observations, and a machine-learning algorithm(4). In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface-models. Our results suggest that global annual evapotranspiration increased on average by 7.1 +/- 1.0 millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Nino event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science

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Section: Methods Summarymentioning

confidence: 99%

Recent decline in the global land evapotranspiration trend due to limited moisture supply

Jung

Reichstein

Ciais

et al. 2010

Nature

1,880

1,462

View full text Add to dashboard Cite

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“…They do not yet contain associated uncertainties or/and updated cloud masking, which is planned for the fourth reprocessing [41,42]. In this work, we use a version with uncertainties.…”

Section: The Jrc Meris Fapar Productmentioning

confidence: 99%

“…This retrieval method assumes that the leaves are alive and photosynthesising, hence the name green FAPAR. We assume that ω l (λ) and the leaf single scattering albedo are fixed to a value representing standard leaves using standard biochemical leaf properties [41,42]. In this study, we average MERIS values over 3 × 3 pixels around the central pixel in order to minimise the impact of remaining clouds and cloud shadow contamination [41,42].…”

Section: The Jrc Meris Fapar Productmentioning

confidence: 99%

Estimation of FAPAR over Croplands Using MISR Data and the Earth Observation Land Data Assimilation System (EO-LDAS)

et al. 2017

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Abstract:The Fraction of Absorbed Photosynthetically-Active Radiation (FAPAR) is an important parameter in climate and carbon cycle studies. In this paper, we use the Earth Observation Land Data Assimilation System (EO-LDAS) framework to retrieve FAPAR from observations of directional surface reflectance measurements from the Multi-angle Imaging SpectroRadiometer(MISR) instrument. The procedure works by interpreting the reflectance data via the semi-discrete Radiative Transfer (RT) model, supported by a prior parameter distribution and a dynamic regularisation model and resulting in an inference of land surface parameters, such as effective Leaf Area Index (LAI), leaf chlorophyll concentration and fraction of senescent leaves, with full uncertainty quantification. The method is demonstrated over three agricultural FLUXNET sites, and the EO-LDAS results are compared with eight years of in situ measurements of FAPAR and LAI, resulting in a total of 24 site years. We additionally compare three other widely-used EO FAPAR products, namely the MEdium Resolution Imaging Spectrometer (MERIS) Full Resolution, the MISR High Resolution (HR) Joint Research Centre Two-stream Inversion Package (JRC-TIP) and MODIS MCD15 FAPAR products. The EO-LDAS MISR FAPAR retrievals show a high correlation with the ground measurements (r 2 > 0.8), as well as the lowest average RMSE (0.14), in line with the MODIS product. As the EO-LDAS solution is effectively interpolated, if only measurements that are coincident with MISR observations are considered, the correlation increases (r 2 > 0.85); the RMSE is lower by 4-5%; and the bias is 2% and 7%. The EO-LDAS MISR LAI estimates show a strong correlation with ground-based LAI (average r 2 = 0.76), but an underestimate of LAI for optically-thick canopies due to saturation (average RMSE = 2.23). These results suggest that the EO-LDAS approach is successful in retrieving both FAPAR and other land surface parameters. A large part of this success is based on the use of a dynamic regularisation model that counteracts the poor temporal sampling from the MISR instrument.

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“…Several studies [4,5,13,14,16,17], have pointed out that the number and representativeness of ground reference data limit the development of remote sensing methods for estimating boreal forest fPAR. Recently, Weiss et al [13] emphasized that ground reference sites with medium to high fPAR values are required to improve the accuracy assessment of global fPAR products.…”

Section: Introductionmentioning

confidence: 99%

Validation of MODIS and GEOV1 fPAR Products in a Boreal Forest Site in Finland

et al. 2015

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Remote sensing of the fraction of absorbed Photosynthetically Active Radiation (fPAR) has become a timely option to monitor forest productivity. However, only a few studies have had ground reference fPAR datasets containing both forest canopy and understory fPAR from boreal forests for the validation of satellite products. The aim of this paper was to assess the performance of two currently available satellite-based fPAR products: MODIS fPAR (MOD15A2, C5) and GEOV1 fPAR (g2_BIOPAR_FAPAR), as well as an NDVI-fPAR relationship applied to the MODIS surface reflectance product and a Landsat 8 image, in a boreal forest site in Finland. Our study area covered 16 km 2 and field data were collected from 307 forest plots. For all plots, we obtained both forest canopy fPAR and understory fPAR. The ground reference total fPAR agreed better with GEOV1 fPAR than with MODIS fPAR, which showed much more temporal variation during the peak-season than GEOV1 fPAR. At the chosen intercomparison date in peak growing season, MODIS NDVI based fPAR estimates were similar to GEOV1 fPAR, and produced on average 0.01 fPAR units smaller fPAR estimates than ground reference total fPAR. MODIS fPAR and Landsat 8 NDVI based fPAR estimates were similar to forest canopy fPAR.

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Uncertainty estimates for the FAPAR operational products derived from MERIS — Impact of top-of-atmosphere radiance uncertainties and validation with field data

Cited by 65 publications

References 35 publications

Recent decline in the global land evapotranspiration trend due to limited moisture supply

Recent decline in the global land evapotranspiration trend due to limited moisture supply

Estimation of FAPAR over Croplands Using MISR Data and the Earth Observation Land Data Assimilation System (EO-LDAS)

Validation of MODIS and GEOV1 fPAR Products in a Boreal Forest Site in Finland

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