How can we better track diurnal photosynthesis using geostationary satellite? A study over the Asia-Oceania flux tower sites

Terrestrial photosynthesis constitutes a crucial component of the global carbon cycle, and its accurate quantification is essential for understanding climate change dynamics. However, current remote sensing monitoring of terrestrial photosynthesis often rely on data with coarse temporal resolution, which cannot adequately capture sub-daily variations in canopy photosynthesis in response to environmental drivers. The hyper-temporal observations enabled by new-generation geostationary satellites offer promising opportunities to monitor canopy photosynthesis with substantially improved temporal resolution and reduced data gaps. In this study, we evaluate the potential of spectral indices and radiation metrics derived from FY4B/AGRI and Himawari-8/AHI at 10/15-minute intervals to track diurnal variations in canopy light use efficiency (LUE) and photosynthesis across more than 50 flux tower sites in the Asia-Oceania region. Geometric, atmospheric, and angular corrections were applied to enhance radiometric consistency. Multiple modeling schemes of varying complexity were tested to determine the optimal parameter combination. Our results indicate that, with rigorous data processing and quality control, FY4B/AGRI and Himawari-8/AHI provide valuable information on diurnal canopy structure, physiological activity, and solar radiation dynamics, enabling reasonably accurate tracking of sub-daily canopy photosynthesis. Furthermore, compared to polar-orbiting satellites such as MODIS, geostationary satellites substantially reduce data gaps, particularly over cloud-prone regions such as tropical and subtropical forests. We suggest that observations from FY4B/AGRI and H8/AHI, in conjunction with flux tower networks, can contribute to a better process understanding of terrestrial carbon cycle over Asia-Oceania region at refined temporal scales.