## 3 Materials and Methods  
### Data  
#### 3.1.1 Remote Sensing Data  
We obtained a time series of 39 images at 30 m resolution from the HLS data product that covered the study area from 1 April to 30 September 2016. The HLS data are atmospherically corrected with spatial coregistration, bidirectional reflectance distribution function normalization, and spectral bandpass adjustments of Landsat-8 MSI and Sentinel-2 OLI sensors. The MSI surface reflectance bands are also adjusted to Landsat-8 characteristics by applying the spectral response function of the OLI sensor. The HLS surface reflectance data product is distributed globally within the Sentinel-2 tiling system and is abbreviated as S30 (obtained from Sentinel-2 MSI sensor) and L30 (obtained from Landsat-8 OLI sensor). For more information about the processing of MSI and OLI observations within the HLS data product, the reader is referred to [PERSON] et al. (2016) and [PERSON] et al. (2010). We included the time series of HLS data available between 11:38 to 11:54 a.m. Central European Time during the 2016 vegetation growing season. Further filtering of the HLS data was performed based on the quality indicators using NDVI and near infrared (NIR) reflectance (see Section 3.2 for more details).  
We also obtained the hyperspectral airborne data over the study area. We compared the retrieval of vegetation properties from both airborne and HLS data to examine if multispectral HLS bands preserve the required information compared to hyperspectral bands. The airborne data were acquired around local solar noon between 11 a.m. and 2 p.m. on 31 August 2016 with two push broom spectroradiometers (Compact Airborne Spectrographic Imager (CASI) and shortwave Infrared (SWIR) Airborne Spectrographic Imager (SASI) from Itres Ltd., Calgary, AB, Canada) onboard the Flying Laboratory of Imaging Systems operated by the Global Change Research Institute (37,38). The CASI operates in the visible and NIR regions between 372 and 1044 nm (72 spectral bands with a sampling distance of 9.4 nm) and a nominal spatial resolution of 1.0 m. SASI operates in the shortwave infrared region between 957 and 2442 nm (100 spectral bands with a sampling distance of 15 nm) and nominal spatial resolution of 2.5 m. The airborne data were corrected radiometrically (using the factory calibration coefficients in RCX software (Itres Ltd., Calgary, AB, Canada)), geometrically (using GeoCorr software (Itres Ltd., Calgary, AB, Canada)), and atmospherically (using ATCOR-4 software (39)), and combined into a single hypercube according to the processing chain established at Global Change Research Institute (37). The quality of the atmospheric corrections was evaluated by comparing the airborne spectra extracted for homogeneous artificial surfaces with spectral signatures measured in the field during the overflight, which produced maximum differences of 3% in NIR and SWIR wavelengths for some targets (Figure S1). Both HLS and airborne data were used to retrieve vegetation properties at the Blly Kriz site (Section 3.2). For this purpose, we extracted the surface reflectance of the vegetation canopy, i.e., top-of-canopy (TOC) reflectance, from the target area delineated by the ecosystem boundary (Section 3.1.2).