Generating high-resolution total canopy SIF emission from TROPOMI data: Algorithm and application

Abstract

Solar-induced chlorophyll fluorescence (SIF) is a rapidly advancing front in modeling global terrestrial gross primary production (GPP). Canopy total SIF emissions (SIFₜₒₜₐₗ) are mechanistically linked to the plant photosynthesis, and can be estimated from satellite observed SIF (SIFₒbₛ) through radiative transfer modeling. However, the current satellite SIFₒbₛ and thus SIFₜₒₜₐₗ are available only at coarse spatial resolutions from several kilometers to tens of kilometers, inhibiting the application at fine spatial scales. Here, we proposed an algorithm to generate both global high-resolution SIFₜₒₜₐₗ (HSIFₜₒₜₐₗ) and high-resolution SIFₒbₛ (HSIFₒbₛ) at 1 km from low-resolution SIFₒbₛ (LSIFₒbₛ) from the TROPOspheric Monitoring Instrument (TROPOMI), which has a spatial resolution at nadir of 3.5 km by 5.6–7 km. Our statistical method is based on the law of energy conservation and uses satellite derived fraction of absorbed photosynthetically active radiation, fluorescence efficiency, and the escape probability of fluorescence. We evaluated the accuracy of our HSIFₜₒₜₐₗ using the Orbiting Carbon Observatory-2 SIF (R² = 0.78). We found that the spatial resolution had clear effects on the relationship between HSIFₜₒₜₐₗ and GPP. We also compared HSIFₜₒₜₐₗ to 8-day averaged tower GPP from 135 flux sites and found that they were better correlated when HSIFₜₒₜₐₗ was averaged over a 1-km radius around the tower than when averaged over a larger radius. Our study provided a unique high-resolution HSIFₜₒₜₐₗ product, which will advance the estimation of GPP by extrapolating site-level relationships to the global scale.

Plant phenotyping relevance

衛星SIFから植物キャノピーの蛍光・光合成関連状態を高解像度で推定するアルゴリズムを開発し、独立データで精度検証しており、植物フェノタイピング手法が中心である。

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