Assessment of Satellite-Derived FAPAR Products With Different Spatial Resolutions for Gross Primary Productivity Estimation

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Abstract
Accurate estimation of Gross Primary Productivity (GPP) is crucial for understanding terrestrial carbon cycles and assessing ecosystem health. Light Use Efficiency (LUE) models, which are widely used for the generation of regional or global GPP products, often rely on Fraction of Absorbed Photosynthetically Active Radiation (FAPAR). However, most existing FAPAR products with moderate to coarse spatial resolutions introduce uncertainties in GPP estimations across heterogeneous landscapes. In this work, the MODerate resolution Imaging Spectroradiometer (MODIS) FAPAR product at the 500-m resolution, along with a newly HIgh spatial resolution Global LAnd Surface Satellite (Hi-GLASS) FAPAR dataset at the 30-m resolution, was used to drive a LUE model for GPP estimations at 188 eddy covariance (EC) sites. Then, they were compared and evaluated based on the EC GPP measurements. Results showed that Hi-GLASS FAPAR provided the GPP estimates with more detailed spatial information compared to MODIS FAPAR. Moreover, the Hi-GLASS FAPAR significantly improved GPP estimations, with an overall R2 increase from 0.54 (MODIS) to 0.63 (Hi-GLASS) and an RMSE decrease from 3.04 to 2.70 gC m−2 day−1. Additionally, 75% of the selected sites exhibited enhanced R² values with Hi-GLASS FAPAR, demonstrating its application potential in GPP estimations across different vegetation types. Specifically, crop sites exhibited the most notable improvements, with an R² increase of 0.16 and an RMSE decrease of 0.70 gC m−2 day−1. These findings highlight the advantages of high-resolution FAPAR data in capturing spatial heterogeneity and improving the accuracy of GPP estimations, and underscore its potential for refined ecosystem monitoring.
Funding Information
  • Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0603)
  • Science and Technology Program of Xizang Autonomous Region, China (XZ202402ZY0026)
  • National Natural Science Foundation of China (42071352)
  • Sichuan Science and Technology Program (2024NSFSC0077)
  • Science and Technology Research Program of Institute of Mountain Hazards and Environment (IMHE-ZYTS-05)

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