# Remote Sensing-Based Multilayer Perceptron Model for Grassland Above-Ground Biomass Estimation
## 3 Data Acquisition and Preprocessing
### Remote Sensing Data Acquisition and Preprocessing
#### 3.1.2 DEM Elevation Data  
The terrain in Xiwuzhumuqin Banner is diverse, ranging from undulating plateaus to low mountain hills. The topographic conditions significantly influence the distribution of grassland biomass. This study introduces Digital Elevation Model (DEM) data to accurately  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Vegetation Index** & **Formulation** & **Cite** \\ \hline Atmospheric Resistant Vegetation Index (ARVI) & \begin{tabular}{l} ARVI = (NIR \(-\) (2 \(\times\) Red) + Blue)/(NIR + (2 \(\times\) \\ Red) + Blue) \\ \end{tabular} & [19] \\ Chlorophyll Index (CIg) & Clg = (NIR/Green) \(-\) 1 & [20] \\ Green Normalized Difference Vegetation & \begin{tabular}{l} GNDVI = (NIR \(-\) Green)/(NIR + Green) \\ \end{tabular} & [21] \\ Index (GNDVI) & \begin{tabular}{l} GNOAVI = 1.16 \(\times\) (NIR \(-\) Green)/(NIR + Green \\ + 0.16) \\ \end{tabular} & [22] \\ Modified Soil-Adjusted Vegetation & \begin{tabular}{l} MSAVI = 1/2 \(\times\) (2(NIR + 1) \(-\) sqrt ((2 NIR + 1) \(\times\) \\ \(2-8\) (NIR \(-\) Red))) \\ \end{tabular} & [23] \\ Modified Vegetation Index (MVI) & \
\begin{tabular}{l} MVI = NIR \(-\) (Red + SWIR)1/NIR + (Red + \\ SWIR) \\ \end{tabular} & [24] \\ Normalized Difference Vegetation Index (NDVI) & NDVI = ((NIR \(-\) Red)/(NIR + Red)) & [25] \\ Difference Vegetation Index (DVI) & DVI = NIR \(-\) Red & [26] \\ Enhanced Vegetation Index (EVI) & EVI = 2.5 (NIR \(-\) Red)/(NIR + 6 Red \(-\) 7.5 Blue \\ + 1) \\ Red–Green Blue Vegetation Index (RGBVI) &
\begin{tabular}{l} RGBVI = (Green\({}^{2}\) \(-\) Red \(\times\) Blue)/(Green\({}^{2}\) + Red \\ \(\times\) Blue) \\ \end{tabular} & [28] \\ \multirow{2}{*}{Transformed Vegetation Index (TVI)} & TVI = 60 \(\times\) (NIR \(-\) Green) \(-\) 100 \(\times\) (Red \\ \(-\) Green) & [29] \\ Ratio Vegetation Index (RVI) & RVI = NIR/Red & [30] \\ \hline \hline \end{tabular} Note: Red: red-band reflectance; Green: green-band reflectance; Blue: blue-band reflectance; NIR: near-infrared band reflectance; SWIRI: shortwave infrared 1 band reflectance.  
\end{table}
Table 1: Vegetation index and formula.  
depict the topographic characteristics of the study area, such as elevation, slope, and aspect, and to analyze their potential impact on grassland biomass.  
DEM data with a spatial resolution of 30 m were downloaded from the Geospatial Data Cloud ([[https://www.gscloud.cn/](https://www.gscloud.cn/)]([https://www.gscloud.cn/](https://www.gscloud.cn/)), accessed on 15 August 2024). The data underwent preprocessing, including mosaicking and clipping, to generate DEM imagery consistent with the administrative boundary of Xiwuzhumuqin Banner. Based on this, slope and aspect, along with other terrain factors, were calculated using ArcMap software v.10.8 and used as important input variables for the grassland biomass inversion model. The spatial distribution of these terrain factors not only reveals the ecological gradient characteristics of the grasslands in the study area but also helps to improve the accuracy of the model's estimates.