Photochemical reflectance index (PRI) can be used to improve the relationship between gross primary productivity (GPP) and sun-induced chlorophyll fluorescence (SIF)

Despite much progress has been made in recent years, the estimation of terrestrial gross primary productivity (GPP) remains highly uncertain. Recent studies have demonstrated the usefulness of sun-induced chlorophyll fluorescence (SIF) from plants for estimating GPP. In this study, the relationships of GPP to SIF and Photochemical Reflectance Index (PRI) under different environmental conditions are established using carbon flux data at 61 sites distributed globally and coincident SIF data from OCO-2 and PRI data from MODIS. We analyzed OCO-2 SIF data at both 757 nm and 771 nm against instantaneous and daily GPP values derived from the tower flux data. Our results for these four cases are similar, and those with SIF at 757 nm and daily GPP show that: (1) a significant relationship is found between GPP and observed SIF (SIFobs) for all vegetation types (R2 = 0.53, RMSE = 4.28 μmol m−2 s−1p