From Canopy‐Leaving to Total Canopy Far‐Red Fluorescence Emission for Remote Sensing of Photosynthesis: First Results From TROPOMI

Abstract

Abstract Solar‐induced chlorophyll fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI), which has substantially improved spatial and temporal resolutions, will improve the global estimations of gross primary production (GPP) than previous satellite SIF data. However, the canopy‐leaving SIF observed by sensors (SIF obs ) represents only a portion of the total canopy SIF emission (SIF total ). This portion is sensitive to the canopy structure and observation direction, resulting in uncertainties in GPP estimations using SIF obs . Here we used the spectral invariant theory to derive global soil‐resistant SIF total (SIF total‐SR ) from TROPOMI SIF obs and evaluated the SIF total‐SR performance in estimating GPP. We found that the clear differences in SIF obs between needleleaf forest and crops diminished for SIF total‐SR . SIF total‐SR increased the coefficient of determination ( R 2 ) by 0.09 and 0.11 against the flux tower instantaneous and daily GPP, respectively. This derived SIF total‐SR can be used to develop more robust GPP models and better constrain carbon cycle models.