Abstract
The fraction of absorbed photosynthetically active radiation (FAPAR) is a critical biophysical parameter in eco-environmental studies. Scaling of FAPAR from the field observation to the satellite pixel is essential for validating remote sensing FAPAR product and for further modeling applications. However, compared to spatial mismatches, few studies have considered temporal mismatches between in-situ and satellite observations in the scaling. This paper proposed a general methodology for scaling FAPAR from the field to the satellite pixel considering the temporal variation. Firstly, a temporal normalization method was proposed to normalize the in-situ data measured at different times to the time of satellite overpass. The method was derived from the integration of an atmospheric radiative transfer model (6S) and a FAPAR analytical model (FAPAR-P), which can characterize the diurnal variations of FAPAR comprehensively. Secondly, the logistic model, which derives smooth and consistent temporal profile for vegetation growth, was used to interpolate the in-situ data to match the dates of satellite acquisitions. Thirdly, fine-resolution FAPAR products at different dates were estimated from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data using the temporally corrected in-situ data. Finally, fine-resolution FAPAR were taken as reference datasets and aggregated to coarse resolution, which were further compared to the Moderate Resolution Imaging Spectroradiometer (MODIS) FAPAR product. The methodology is validated for scaling FAPAR from the field to the satellite pixel temporally and spatially. The MODIS FAPAR manifested a good consistency with the aggregated FAPAR with R2 of 0.922 and the root mean squared error of 0.054.
Highlights
The Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) describes the efficiency of light absorption by plant and is a critical biophysical parameter in eco-environmental studies [1,2]. It is defined as the fraction of Photosynthetically Active Radiation (PAR) absorbed by vegetation, where PAR refers to the incoming solar radiation within the spectral range 0.4–0.7 μm [3]
FAPAR-P model, which is interesting for further considerations on temporal correction issues
As the measurements of skylight proportions were unavailable here, the skylight proportions were decomposed into the part affected by solar zenith angle (SZA) and the part affected by atmosphere
Summary
The Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) describes the efficiency of light absorption by plant and is a critical biophysical parameter in eco-environmental studies [1,2]. It is defined as the fraction of Photosynthetically Active Radiation (PAR) absorbed by vegetation, where PAR refers to the incoming solar radiation within the spectral range 0.4–0.7 μm [3]. SPOT-VEGETATION [10] and the Medium Resolution Imaging Spectrometer (MERIS) [11] The validity of these satellite FAPAR products makes FAPAR a key terrestrial remote sensing product in the Global Climate Observing System [12]. In Production Efficiency Models (PEMs) for Gross and Net Primary Productivity (GPP/NPP), FAPAR often acts as the only satellite derived variable [5]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
