CSIF and GOSIF Do Not Accurately Capture the Vegetation Greening During the Spring of 2020

In the spring of 2020, lockdown measures were adopted to control the spread of novel coronavirus, and these measurements had large impacts on air quality, regional climate, and vegetation growth. Accurately capturing the response of vegetation to environmental changes is crucial for ecosystem research. However, there might be some divergences in vegetation growth trends from different satellite datasets. To investigate the response of vegetation growth to environmental changes from January to April 2020, we employed two reconstructed solar-induced chlorophyll fluorescence (SIF) products, continuous SIF (CSIF) and global OCO-2 SIF (GOSIF), normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and leaf area index (LAI). Results shows that CSIF, GOSIF, NDVI, EVI, and LAI captured enhanced vegetation growth during January-March 2020 compared with 2015-2019. However, CSIF and GOSIF show an opposite trend to vegetation indices (VIs) and LAI in April. The trends from CSIF and GOSIF also differed with those from TROPOspheric Monitoring Instrument (TROPOMI) SIF and OCO-2 SIF. Biases were attributed to the input MODIS surface reflectance data for reconstructing SIF in the algorithms of GOSIF and CSIF.