# Monitoring Forest Diversity under Moso Bamboo Invasion: A Random Forest Approach
## 2 Materials and Methods
### Remote Sensing Data
#### 2.2.3 Pre-Processing and Extracting Features from SRTM Topographic Data  
NASA's production of SRTM digital elevation data signifies a notable progression in the realm of global digital elevation mapping. This dataset facilitates access to superior elevation information, particularly covering extensive regions within the tropics and other developing areas [40]. The SRTM topographic data, sourced from the USGS EROS Data Center on 5 August 2022 ([[https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/)]([https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/))), offer comprehensive global coverage. These elevation data offer global coverage with void-filled information at a resolution of 1 arc-second (approximately 30 m) [41], comprising a high-resolution dataset on a worldwide scale. To ensure consistency with the image data, SRTM topographic data were reprojected into UTM/WGS84 from the original projection system of GCS/WGS84. We also resampled the SRTM data from 30 m resolution to 10 m resolution and extracted the elevation, slope, and aspect using ArcGIS software (version 10.8, ESRI, Redlands, CA, USA).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Bands** & **Name** & **Central** & & **Spatial Resolution** \\  & & **Wavelength** & **Bandwidth (nm)** & **(m)** \\ \hline B2 & Blue & 490 & 65 & 10 \\ B3 & Green & 560 & 35 & 10 \\ B4 & Red & 665 & 30 & 10 \\ B5 & Red-edge 1 & 705 & 15 & 20 \\ B6 & Red-edge 2 & 740 & 15 & 20 \\ B7 & Red-edge 3 & 783 & 20 & 20 \\ B8 & Near-infrared 1 & 842 & 115 & 10 \\ B8a & Near-infrared 2 & 865 & 20 & 20 \\ B11 & Short-wave infrared 1 & 1610 & 90 & 20 \\ B12 & Short-wave infrared 2 & 2190 & 180 & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Sentinel-2 MSI band characteristics defined by the European Space Agency at 10 m and 20 m spatial resolution.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Abbreviation** & **Name** & **Equation** & **Citation** \\ \hline NDVI & Normalized Difference Vegetation Index & NDVI = NIR \(-\) RED/NIR \(+\) RED & [28] \\ NDWI & Normalized Difference Water Index & NDWI = NIR \(-\) SWIR\(-\)/NIR\(+\) SWIR2 & [29] \\ CRI1 & Carotenfold reflectance Index 1 & CRI1 = 1/BLU \(-\)/Green & [30] \\ CDVI & Green Difference Vegetation Index & CDVI = NIR \(-\) GREEN & [31] \\ GNDVI & Green Normalized Difference Vegetation Index & GNDVI = \((\)NIR \(-\) GREEN\()\()/(\)NIR \(+\) GREEN\()\) & [32] \\ GRVI & Green Ratio Vegetation Index & CRVI = NIR/GREEN & [31] \\ CIgreen & Green chlorophyll index & Clgren = NIR/GREEN \(-\) 1 & [33] \\ RGRI & Red Green Ratio Index & RGRI = RED/GREEN & [34] \\ DVI & Difference Vegetation Index & DVI = NIR \(-\) RED & [35] \\ NLI & Non-Linear Index & NLI = NIR\({}^{2}\) \(-\) RED/NIR\({}^{2}\) \(+\) RED & [36] \\ SAVI & Soil Adjusted Vegetation Index & SAVI = 1.5 \(\times\) (NIR \(-\) RED) /(NIR \(+\) RED \(+\) L) & [37] \\ SRI & Simple Ratio Index & SRI = NIR/RED & [38] \\ EVI & Enhanced Vegetation Index & EVI = 2.5 \(\times\) (NIR \(-\) RED/NIR \(+\) 6 RED \(-\) 7.5 BLUE \(+\) 1) & [39] \\ \hline \hline \end{tabular}
\end{table}
Table 2: List of vegetation indices and corresponding formulas and references.