Sensitivity of Estimated Total Canopy SIF Emission to Remotely Sensed LAI and BRDF Products

Remote sensing of solar-induced chlorophyll fluorescence (SIF) provides new possibilities to estimate terrestrial gross primary production (GPP). To mitigate the angular and canopy structural effects on original SIF observed by sensors (SIF obs ), it is recommended to derive total canopy SIF emission (SIF total ) of leaves within a canopy using canopy interception ( $i_0$ ) and reflectance of vegetation ( $R_{\text{V}}$ ). However, the effects of the uncertainties in $i_0$ and $R_{\text{V}}$ on the estimation of SIF total have not been well understood. Here, we evaluated such effects on the estimation of GPP using the Soil-Canopy-Observation of Photosynthesis and the Energy balance (SCOPE) model. The SCOPE simulations showed that the $R^2$ between GPP and SIF total was clearly higher than that between GPP and SIF obs and the differences in $R^2$ ( $\Delta R^2$ ) tend to decrease with the increasing levels of uncertainties in $i_0$ and $R_{\text{V}}$ . The resultant $\Delta R^2$ decreased to zero when the uncertainty level in $i_0$ and $R_{\text{V}}$ was ~30% for red band SIF (RSIF, 683 nm) and ~20% for far-red band SIF (FRSIF, 740 nm). In addition, as compared to the TROPOspheric Monitoring Instrument (TROPOMI) SIF obs at both red and far-red bands, SIF total derived using any combination of $i_0$ (from MCD15, VNP15, and CGLS LAI products) and $R_{\text{V}}$ (from MCD34, MCD19, and VNP43 BRDF products) showed comparable improvements in estimating GPP. With this study, we suggest a way to advance our understanding in the estimation of a more physiological relevant SIF datasets (SIF total ) using current satellite products.