Sensitivity of Estimated Total Canopy SIF Emission to Remotely Sensed LAI and BRDF Products
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abstract
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 (
i0
) and reflectance of vegetation (
RV
). However, the effects of the uncertainties in
i0
and
RV
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
R2
between GPP and SIF
total
was clearly higher than that between GPP and SIF
obs
and the differences in
R2
(
ΔR2
) tend to decrease with the increasing levels of uncertainties in
i0
and
RV
. The resultant
ΔR2
decreased to zero when the uncertainty level in
i0
and
RV
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
i0
(from MCD15, VNP15, and CGLS LAI products) and
RV
(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.
