Cross-ECV consistency at global scale: LAI and FAPAR changes

Area of Science:

• Earth Observation
• Climate Science
• Remote Sensing

Background:

• Terrestrial Essential Climate Variables (ECVs) like Leaf Area Index (LAI) and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) are crucial for global environmental monitoring.
• Assessing the physical consistency between different ECVs products is vital for reliable climate change studies.

Purpose of the Study:

• To propose and validate a framework for assessing the physical consistency between terrestrial ECVs products derived from Earth Observation.
• To evaluate the agreement between temporal variations of Leaf Area Index (LAI) and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) products from various sources.

Main Methods:

• Developed a methodology to classify simultaneous changes in LAI and FAPAR based on sign, magnitude, and confidence, incorporating product uncertainties.
• Introduced agreement metrics to identify spatial and temporal biases, including non-coherency, non-significance, and sensitivity.
• Applied the framework to JRC-TIP, CGLS (SPOT/VGT, Proba-V), and MODIS MCD15A3 products at native resolutions and aggregated scales over Southern Africa.

Main Results:

• Copernicus Global Land Service (CGLS) LAI and FAPAR products exhibited spatial/temporal inconsistencies and trend biases.
• MODIS MCD15A3 products showed the most non-coherent changes, primarily in the Eastern Hemisphere.
• Joint Research Center (JRC)-TIP products demonstrated high consistency between LAI and FAPAR.

Conclusions:

• Physically-based retrieval algorithms (JRC-TIP, MODIS) generally yield more consistent ECVs products.
• Uncertainty-based weighted averaging of aggregated products enhances agreement between ECVs changes, with exceptions noted for MODIS over forests.