## Materials and Methods
### Data Collection
#### 2.2.2 Sentinel-2 Satellite Multispectral Image  
The sentinel satellites are a central part of global monitoring for environment and security (GMES), also known as the Copernican program run by European Space Agency (ESA). Sentinel-2 A/B are the second sets of satellites launched in 2015 and 2017 separately, carrying the multispectral instrument (MSI) [36]. They form a satellite constellation in a sun-synchronous orbit at a 180\({}^{\circ}\) phase difference, in order to shorten the return cycle of the satellite and improve the efficiency of its dynamic observation, with an altitude of 786 km, an orbital inclination of 98.62\({}^{\circ}\), an image width of 290 km, and an orbital period of 100 min. Twelve detecting elements are arranged along the scanning direction of the MSI sensor, and the ground reflection solar spectrum within the scanning band is acquired simultaneously by means of push-sweep scanning. MSI consists of 13 spectral bands ranging from 400 to 2400 nm, which cover the electromagnetic spectrum from visible light to short-wave infrared in a narrow channel width. Bands can be divided into 10 m, 20 m and 60 m resolutions according to spatial resolution. Bands with different resolutions have different purposes. Among the optical data, Sentinel-2 is the only satellite with three bands in the red edge range [37], which is very effective for monitoring vegetation health information. See Table 1 for details. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Spatial** \\ **Resolution** \\ \end{tabular} & \begin{tabular}{c} **Spectral** \\ **Band** \\ \end{tabular} & \begin{tabular}{c} **Central** \\ **Wavelength (nm)** \\ \end{tabular} & \begin{tabular}{c} **Bandwidth** \\ **(nm)** \\ \end{tabular} & \begin{tabular}{c} **Band Names** \\ \end{tabular} & \begin{tabular}{c} **Application Fields** \\ \end{tabular} \\ \hline \multirow{3}{*}{**10 m**} & B2 & 490 & 65 & Blue & Epcontinental monitoring \\ \cline{2-5}  & B3 & **560** & **38** & Green & Marine monitoring \\ \cline{2-5}  & B4 & 665 & 30 & Red & The polar monitoring \\ \cline{2-5}  & B8 & **842** & **115** & NIR & \\ \hline \multirow{3}{*}{**20 m**} & B5 & 705 & 15 & Vegetation Red Edge & \multirow{3}{*}{\
\begin{tabular}{c} Vegetation monitoring \\ Environmental monitoring \\ \end{tabular} } \\ \cline{2-5}  & B6 & **740** & 15 & Vegetation Red Edge & Vegetation monitoring \\ \cline{2-5}  & B7 & 775 & 20 & Vegetation Red Edge & Environmental monitoring \\ \cline{2-5}  & B8a & **865** & **20** & NIR & \\ \cline{2-5}  & B11 & 1610 & 90 & SWIR & Ice monitoring \\ \cline{2-5}  & B12 & **2190** & **180** & SWIR & Vegetation monitoring \\ \hline \multirow{3}{*}{**60 m**} & B1 & 443 & 20 & Coastal aerosol & \multirow{3}{*}{
\begin{tabular}{c} Atmospheric correction (aerosol, water vapor, cirrus) \\ \end{tabular} } \\ \cline{2-5}  & B9 & **940** & 20 & Water vapour & \\ \cline{1-1} \cline{2-5}  & B10 & 1375 & 30 & SWIR-Cirrus & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Attributes of Sentinel-2 A/B satellite’s 13 bands. Figure 1: Study site location (**a**) and hyperspectral data (R: 650 nm, G: 562 nm, B: 470 nm) by a UAV imaging spectrometer (**b**) with detailed canopies of Pinus (**c**) and Larix (**d**). Three bands related to vegetation red edge (B5, B6, B7) can be used for monitoring the status and health of plant pigment. They also have narrow bandwidth (15 nm for B5 and B6, 20 nm for B7) and similar central wavelength comparing to the UAV hyperspectral data used in the study. As a result, the Sentinel-2 multispectral image can be utilized to test the adaptation and application ability of the proposed Normalized Difference Canopy Shadow Index to differentiate different shadow circumstances of a vegetation canopy quantitatively and distinguish sunlit vegetation canopy from shaded ones and soil backgrounds. Under the Copernicus program's data policy, Sentinel-2 A/B's level-1B and level-1C data can be downloaded for free to users worldwide.