LAUSR

Abstract Solar-Induced chlorophyll Fluorescence (SIF) can serve as an early and non-invasive indicator of the functioning and status of vegetation due to its close link to photosynthetic activity. Most existing approaches retrieve SIF at around few discrete absorption lines. However, the full SIF spectrum can provide more information on the functional status of photosynthetic machinery. European Space Agency's FLuorescence EXplorer (FLEX) mission, to be launched in 2022, is dedicated to the accurate reconstruction of the full SIF spectrum over land and incorporates the heights and positions of the two SIF peaks and the total fluorescence emission (spectrally-integrated value) into planned Level-2 products. In this paper, an advanced Fluorescence Spectrum Reconstruction (aFSR) method was proposed to reconstruct the full SIF spectrum by capitalizing on the features of existing methods. The aFSR method used linear combinations of basis spectra to approximate the spectra of SIF and the reflectance factor and exploited all available bands within the spectral range of SIF emission for spectral fitting of SIF and reflected radiance. The number of basis spectra of the reflectance factor used was self-adaptively determined based on the Bayesian information criterion. A comprehensive intercomparison between the aFSR method and three other methods (i.e., the Fluorescence Spectrum Reconstruction method, the Full-spectrum Spectral Fitting Method, and the SpecFit method) was performed using simulated and experimental datasets. For simulated datasets, the impact of spectral resolution (SR), signal-to-noise ratio (SNR), atmospheric correction, canopy structure, leaf biochemical parameters and directional effect on the accuracy of SIF spectrum reconstruction was considered. Results show that while all methods could achieve the accuracy standard set by the FLEX mission (average absolute relative error of spectrally-integrated SIF