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

Abstract

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.

Remotely Sensed Land Surface Temperature-Based Water Stress Index for Wetland Habitats

“…Measurements of relative chlorophyll content allow information to be obtained on vegetation condition in a given area. On the other hand, because water deficit leads to a reduction in biomass accumulation, the criteria of plant productivity should also be used [67]. Therefore, in this research, as an indicator of water stress, groundwater level, soil moisture, fAPAR, and CCI were used.…”

“…It can be found in the literature that values of fAPAR and CCI correspond to changes in plant condition related to its water stress [66,67]. Its intensity depends on the stress rate and duration [56].…”

Seasonal evolution of soil and plant parameters on the agricultural Gebesee test site: a database for the set-up and validation of EO-LDAS and satellite-aided retrieval models

“…5e. and absolute reflectance factors r from which the MERIS Terrestrial Chlorophyll Index (MTCI) following Dash and Curran (2004) was calculated (Eq. 9).…”

“…In the inverse mode, Earth Observation data are interpreted in terms of soil and vegetation parameters, while prior information is introduced to diminish the uncertainty of retrieved parameters (cf. Chernetskiy et al, 2017).…”

Can We Use the QA4ECV Black-sky Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) using AVHRR Surface Reflectance to Assess Terrestrial Global Change?

“…The state and the evolution of terrestrial vegetation are characterized by a large number of physical, biochemical, and physiological variables. Few of these are directly observable from space, but they jointly determine the fraction of absorbed photosynthetically active radiation (FAPAR) that acts as an integrated indicator of the status and health of plant canopies and can be retrieved by space remote sensing techniques [2][3][4]. FAPAR plays a critical role in the global carbon cycle and in the determination of the primary productivity of the biosphere [5][6][7].…”