## 2 Material and Method
### Measurement of Hyperspectral and Vegetation Properties  
The top of canopy (TOC) spectra were collected periodically (around noontime, under clear sky conditions, from nadir position) through the hyperspectral system Piccolo Doppio [27]. This system has a Dual Field Of View (DFOV) with cosine corrected forequtics to capture down-welling irradiance and the upwelling radiance. In the system, a double bifurcated fiber optic is used to transfer light from the forequtics to the spectrometers; therefore, each spectrometer receives light from the same Earth surface area (each measurement has the same footprint, which is critical for the accuracy of reflectance and SIF estimations and their relationships). The system consists of two hyperspectral spectrometers; the first is FLAME-T-VIS_NOR of Ocean Optics, Dunedin, FL, USA (Spectral range 400-1000 nm; with a full-width half maximum \"FWHM\" 1.3 nm) from where the spectra were collected to calculate VIs shown in Table 1. The second spectrometer is the QEProFL Spectrometer (Spectral range 640-780 nm, with FWHM 0.31 nm) of Ocean Optics USA, designed to measure the spectral region, which contains the O\({}_{2}\)-A and O\({}_{2}\)-B bands to calculate SIF at both peaks of 740 nm and 680 nm. The SIF was calculated with the improved Fraunhofer Line Depth (iFLD) methods (as described in [PERSON] et al. [28]). Three replicates in three technical replicates (i.e., a total of 9 spectra from 3 points within each plot) were measured from the nadir position, where upwelling optics was approximately at 1.4 m above the peat surface with a field of view of 0.62 m. Per point 5 spectra were collected, where the first and last spectra were for dark current (with a closed optical shutter), whereas the middle three spectra were collected with an open shutter. The irradiance and radiance were calculated after subtracting the dark current and applying the calibration factor provided by National Institute for Laser, Plasma and Radiation Physics (NIFLPR), Romania. The reflectance spectra were calculated by dividing radiance by irradiance, and an average of nine spectra from each plot was calculated to minimize the noise and used for modeling purposes.  
The LAI was non-destructively estimated from each plot using a widely used SunScan plant-canopy analyzer system (Delta-T, Burwell, UK). The LAI used here represents a one-sided leaf area divided by a unit of horizontal surface area. The protocol followed for the measurement is described in [PERSON] et al. [31]. LAI measured through SunScan represents the plant area index (PAI) of vascular plants. There was no way to measure masses LAI through this instrument, whereas differentiation of non-green and green LAI was also not possible by using only the SunScan device. Due to the malfunction of SunScan in October, the measurements were taken only till September 2021.  
The CCM 300 (OPTTI-SCIENCES, Hudson, NH, USA) device was used to measure the chlorophyll content of different species on different plots and sites. The data was not directly used as the plant distribution was different in different plots, but it provided the idea of the expected range of chlorophyll content of peatland vegetation for different species.