## Appendix A Fluorescence Retrieval
### Performance of the Retrieval Algorithm  
In order to test the performance of the method, we carried out retrieval tests on simulated canopy radiance spectra. TOC reflectance and fluorescence spectra were generated using SCOPE v1.60 [26]. The SCOPE model is a simulation model for radiative transfer, photosynthesis, and energy fluxes in vegetation and soil. SCOPE has numerous input parameters to describe canopy architecture, photosynthesis parameters, observational, and meteorological conditions. We limited our investigations to cases that are mostly representative of the experimental conditions of the study. Variable values were used for LAI, maximum carboxylation capacity (Vcmo), and soil spectrum (spectrum), and combined together to produce a set of 36 fluorescence and reflectance spectra (Figure 1). All others parameters were kept constant, and their values were determined (whenever possible) from field measurements (Table 1). It should be noted that--despite the high values of LAI (\(LAI_{MAX}=7\)) and the relative high chlorophyll content (40 \(\mu\)g\(\cdot\)cm\({}^{-2}\)) used in the simulations--the maximum fluorescence level is much lower than those previously found in [PERSON] et al. [53] with version v1.40 of the SCOPE model. This difference is particularly large in the red. The red peak is about ten times that in v1.60. As irradiance levels are similar, this is probably due to the implementation of a different leaf fluorescence model in v1.60 compared to v1.40. The solar incident irradiance spectrum was computed at a spectral resolution of 1 cm\({}^{-1}\) from the FLEX-S3_std.atm file, provided in the SCOPE v1.60 package. This file contains a set of 18 atmospheric transfer functions (the so-called T1-T18 system) that are used to compute solar irradiance and atmospheric radiances [66]. Here, we neglect the contribution of the surrounding environment in the sky radiance. Hence, the radiance of a white Lambertian reference surface was computed as the sum of the contributions of the direct sunlight (\(E_{sun}\)) and sky irradiance (\(E_{sky}\)), as:  
\[L^{WREF}=\frac{1}{\pi}(E_{sun}+E_{sky})=t_{1}(t_{4}+t_{5}) \tag{10}\]  
where \(t_{i}\) are atmospheric transfer functions at 1 cm\({}^{-1}\) resolution: \(t_{1}\) is the solar extraterrestrial equivalent radiance, \(t_{4}\) the atmospheric transmittance for direct light, and \(t_{5}\) the diffuse scattering function for direct light. In this case, the irradiance level corresponds approximatively to a PAR level of \(1400\ \mathrm{\SIUnitSymbolMicro mol}\cdot\mathrm{m}^{-2}\cdot\mathrm{s}^{-1}\). The TOC radiance is computed from \(L^{WREF}\), canopy reflectance (\(\rho\)), and canopy SIF (\(SIF_{c}\)) as:  
\[L^{TOC}=\rho\,L^{WREF}+SIF_{c} \tag{10}\]  
TOC and white reference spectra were subsequently convolved with the spectrometer instrumental spectral function (ISF), and noise was added according to the noise model of the spectrometer (Figure 10) to give simulated radiance spectra comparable to the experimental ones. The ISF function was assessed by measuring the narrow emission of the Ar line at 686.8086 nm, which is close to the O\({}_{2}\)-B band. The measured spectrum was fitted by a Gaussian function (FWHM = 0.41 nm). A slightly larger value (0.50 nm) was found for FWHM at 760 nm. The noise level of the spectrometer was assessed by computing the standard deviation of repeated measurements (\(n>500\)) from a halogen source at different intensity levels. It was found that that for a given output value and after dark correction, the noise level was independent of the wavelength channel and of the integration time. It only depends on the output value given by the spectrometer, which is representative of the number of photons accumulated at the detector level during the integration time. The noise was added considering that the best signal-to-noise ratio (SNR) was achieved at the maximum of the acquired spectrum.