Accelerating Fluspect With an Analytical Algorithm in Simulating Mesophyll Fluorescence Matrices

Vegetation solar-induced chlorophyll fluorescence (SIF) is linked to photosynthetic activities and has shown great potential for studying the global carbon cycle. As the most widely used leaf chlorophyll fluorescence radiative transfer model, Fluspect has been extensively used in the exploration and application of chlorophyll fluorescence. The computational efficiency of Fluspect greatly influences its practicability because the leaf-level Fluspect model is the core of fluorescence simulations. However, a numerical algorithm with iterations required was adopted in Fluspect to calculate mesophyll fluorescence matrices. This study revealed that the numerical algorithm is the most time-consuming part (~98%) of Fluspect and proposed an analytical algorithm to replace it. The two algorithms are equivalent, but the analytical algorithm uses 90% less time. Similarly, in a test over a newly collected leaf fluorescence dataset, the inversion of Fluspect achieves an 86% decrease in computational time after incorporating the analytical algorithm. With this updated algorithm, the computational efficiency and practicability of Fluspect are significantly improved and will better serve SIF-related studies.