In a study led by Professor LIU Liangyun from the Aerospace Information Research Institute (AIR) of the Chinese Academy of Sciences, researchers developed a satellite dataset known as the temporally consistent solar-induced fluorescence (TCSIF) dataset, offering a more reliable way to track changes in vegetation and photosynthesis across the globe from 2007 to 2021.
This study, published in Earth System Science Data, provided new insights into the global ecosystem health and productivity over the past 15 years. Photosynthesis is the process by which plants use light energy and carbon dioxide to produce oxygen and organic compounds. Solar-induced chlorophyll fluorescence (SIF) is a type of light emitted by plants during photosynthesis. Measuring this glow from space helps the researchers estimate the rate of photosynthesis on a global scale. By tracking SIF, the researchers can better understand how much carbon dioxide plants are absorbing, which is crucial for studying climate change.
The SIF product obtained from the global ozone monitoring experiment-2A (GOME-2A) satellite has gained widespread popularity, particularly due to its extensive global coverage since its operation in 2007. Over time, however, the instrument's sensitivity degraded, posing challenges for the researchers relying on its data.
To overcome this problem, the researchers used a technique called "temporal degradation correction," which involved normalizing the instrument's degradation by comparing it with data from a stable site in the Sahara Desert. This recalibration made the GOME-2A data consistent and reliable once again.
By using the corrected data, the researchers developed the TCSIF dataset to measures SIF. The TCSIF dataset aligns closely with other SIF products, such as NASA's OCO-2 and TROPOMI, indicating its accuracy and reliability.
The study identified a 16.21% degradation in near-infrared radiance from 2007 to 2021. By normalizing the instrument's degradation during that period, the radiance spectra of GOME-2A were successfully corrected. Based on the calibrated radiance, the researchers were able to develop the TCSIF dataset spanning decades for use in research.
After undergoing the temporal correction, the vegetation SIF increased by 0.70% per year from 2007 to 2021. Notably, about 62.91% of the global vegetated regions saw an increase in SIF, suggesting an overall increase in vegetation SIF and photosynthesis during the growing season.
Compared to the widely used normalized difference vegetation index (NDVI), the TCSIF dataset provided results that were more closely aligned with gross primary productivity (GPP), a measure of the total amount of carbon dioxide that vegetation converts to organic material through photosynthesis, indicating that TCSIF is a more reliable indicator of vegetation health and activity than NDVI.
These results represent a significant advancement in our ability to accurately assess long-term changes in vegetation SIF on a global scale. The TCSIF product can serve as a valuable reference for past and future studies of long-term SIF products and provide important insights into the impact of climate change on vegetation photosynthesis.
Map of trends in the annual average solar-induced chlorophyll fluorescence for 2007–2021. (Image by AIR)
