Comment on amt-2021-66

Abstract

Solar-induced chlorophyll fluorescence (SIF) is emitted during photosynthesis in plant leaves. It constitutes a small additional offset to reflected radiance and can be observed by sensitive instruments. The Chinese global carbon dioxide monitoring satellite (TanSat), as its mission, acquires greenhouse gas column density. The advanced technical characteristics of the hyper-spectrum grating spectrometer (ACGS) onboard TanSat enable SIF retrieval from space observations in the O2-A band. In this study, one-year SIF data was processed from Orbiting Carbon Observatory-2 (OCO-2) and TanSat using a physical-based algorithm. A comparison between the SIF retrieved from OCO-2 and its official product shows their strong linear relationship (R2 > 0.85) and suggests the reliability of the algorithm. The global distribution showed that the SIF retrieved from the two satellites shared the same spatial pattern for all seasons with the grided SIF difference less than 0.3 W m−2 μm−1 sr−1, and they also agreed with the official OCO-2 SIF product. The retrieval uncertainty of seasonal-grided TanSat SIF is less than 0.03 W m−2 μm−1 sr−1 whereas the uncertainty of each sounding ranges from 0.1 to 0.6 W m−2 μm−1 sr−1. The relationship between SIF and terrestrial gross primary productivity was also estimated for data quality testing. The spatiotemporal consistency between TanSat and OCO-2 and their comparable data quality make the comprehensive usage of the two mission products possible. Data supplemented by TanSat observations are expected to contribute to the development of global SIF maps with more spatiotemporal detail, which will advance global research on vegetation photosynthesis.