## 2 Material and Methods
### Retrieval of Sun-Induced Chlorophyll Fluorescence  
The red and far-red fluorescence maps from the HyPlant sensor were computed based on the Spectral Fitting Methods (SFM) described in [PERSON] et al. (2018). The retrieval algorithm, originally developed and \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Vegetation Indices** & **Proxy** & **Formula** & **References** \\ \hline Simple Ratio (SR) & _Greenness_ & \(SR=\frac{R_{\mathcal{O}\text{res}-850}}{R_{\mathcal{O}\text{res}-840}}\) & [(49)] \\ \hline Normalized Difference & _Greenness_ & \(NDVI=\frac{R_{\mathcal{O}\text{res}-830}R_{\mathcal{O}\text{res}-840}}{R_{ \mathcal{O}\text{res}-840}+R_{\mathcal{O}\text{res}-840}}\) & [(50)] \\ Vegetation Index (NDVI) & _Biomass_ & \(2.5\left[\frac{EVI}{EVI}=\frac{1}{R_{\mathcal{O}\text{res}-840}R_{\mathcal{O} \text{res}-840}}\right]\) & [(51)] \\ Index (EVI) & _xanthophyll cycle_ & \(PRI=\frac{R_{\mathcal{O}\text{res}-85}R_{\mathcal{O}\text{res}-85124.5}}{R_{ \mathcal{O}\text{res}-840}+R_{\mathcal{O}\text{res}-840}-7.5R_{\mathcal{O}\text {res}-840}+1}\) & [(52)] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Vegetation indices calculated from HyPlant DUAL data. R in formulas represents the reflectance. Numbers refer to wavelengths in nm. tested for the FLEX mission, was further adapted for airborne observations. The algorithm used the high spectral resolution imagery detected by the HyPlant FLUO module. The technique relied on the analysis of the radiance spectra in high spectral resolution at the O\({}_{2}\) absorption bands (O\({}_{2}\)-A and O\({}_{2}\)-B at 760 and 687 nm, respectively), where the fluorescence contribution to the overall canopy emerging radiance was larger. The pre-processing steps consisted of the radiometric and spectral calibration, correction of detector non-linearity and the deconvolution of the instrument point-spread-function (PSF). The latter referred to the imagery processing technique used to remove stray-light (i.e., scattered light inside the spectrometer) caused by the optical elements of the instrument. In particular, the actual instrument PSF was characterized in the laboratory before the airborne survey and an adapted version of the Van-Cittert algorithm was applied. The fluorescence retrieval approach consisted of two main components: i) The atmospheric radiative transfer was computed through MODTRAN5 (MODerate resolution atmospheric TRANsmission) Radiative Transfer (RT) model; while ii) the decoupling of reflected and fluorescence radiances was achieved based on the spectral fitting technique. The atmospheric RT modelling and surface reflectance/fluorescence were coupled according to [PERSON] et al. [PERSON] et al. (2018). Basically, the retrieval was carried out at sensor-level, comparing the HyPlant and the forward-modelled radiance spectrum in defined spectral windows. The SFM algorithm was adapted considering the specific technical characteristics of HyPlant, exploiting the full set of spectral bands available around the oxygen absorption features. Specifically, the fluorescence retrieval at the O\({}_{2}\)A and O\({}_{2}\)B bands was achieved independently, considering two separate spectral windows (a few tens of nanometers wide) centered around the main absorption features. In particular, the SFM module implemented for HyPlant relied on third-order polynomial and pseudo-Voigt functions to approximate reflectance and fluorescence spectral behavior, respectively. As described in [PERSON] et al. (2018), the pseudo-Voigt function (i.e., weighted linear combination of a Lorentzian and Gaussian) is a convenient approach to approximate the computationally demanding Voigt function and thus limiting the over-processing time to retrieve fluorescence. The atmospheric parameters required to run MODTRAN5 simulations were derived from Microtops II sunphotometer (Solar Light Company, Inc. Glenside, PA, USA ) measurements collected simultaneously to the airborne survey.