The scattering and re-absorption of red and near-infrared chlorophyll fluorescence in the models Fluspect and SCOPE

Abstract

Scattering and re-absorption have been recognized as relevant aspects for the interpretation of solar induced chlorophyll fluorescence (SIF) in vegetation remote sensing. In an earlier study [Yang and Van der Tol, RSE 215, 97-108, 20181 we addressed the problem of scattering and re-absorption of near-infrared fluorescence in the vegetation canopy. In this study we analyse within-leaf re-absorption of both red and near-infrared fluorescence using the radiative transfer model Fluspect. The leaf scattering determines the ratio of backward to total leaf fluorescence emission F-b/(F-b + F-f). Fluspect reproduces this ratio with an RMSE of less than 0.1, and explains the observed dependence of the spectral shape of this ratio on chlorophyll content and other leaf properties. We further provide a theoretical evaluation of how asymmetric SIF emission affects the SIF of a whole canopy and explain why recent within-canopy scattering models for fluorescence are not valid for red SIF.