A Spectral Fitting Algorithm to Retrieve the Fluorescence Spectrum from Canopy Radiance

Abstract

Retrieval of Sun-Induced Chlorophyll Fluorescence (F) spectrum is one of the challenging perspectives for further advancing F studies towards a better characterization of vegetation structure and functioning. In this study, a simplified Spectral Fitting retrieval algorithm suitable for retrieving the F spectrum with a limited number of parameters is proposed (two parameters for F). The novel algorithm is developed and tested on a set of radiative transfer simulations obtained by coupling SCOPE and MODTRAN5 codes, considering different chlorophyll content, leaf area index and noise levels to produce a large variability in fluorescence and reflectance spectra. The retrieval accuracy is quantified based on several metrics derived from the F spectrum (i.e., red and far-red peaks, O2 bands and spectrally-integrated values). Further, the algorithm is employed to process experimental field spectroscopy measurements collected over different crops during a long-lasting field campaign. The reliability of the retrieval algorithm on experimental measurements is evaluated by cross-comparison with F values computed by an independent retrieval method (i.e., SFM at O2 bands). For the first time, the evolution of the F spectrum along the entire growing season for a forage crop is analyzed and three diverse F spectra are identified at different growing stages. The results show that red F is larger for young canopy; while red and far-red F have similar intensity in an intermediate stage; finally, far-red F is significantly larger for the rest of the season.

Plant phenotyping relevance

作物群落の蛍光スペクトルから植物の生理状態を推定する検索アルゴリズムを開発し、シミュレーションと圃場分光測定で精度・信頼性を検証しているため、植物フェノタイピング手法が中心です。

Code and data availability

The paper's spectral fitting (SpecFit) retrieval algorithm is the core computational analysis of this study, and the authors explicitly state its Matlab source code is publicly available via a GitLab repository. No phenotype datasets or field measurement data are stated as publicly deposited.