# Monitoring Cropland Abandonment in Hilly Areas with Sentinel-1 and Sentinel-2 Timeseries
## 2 Materials and Methods
### Datasets  
#### 2.2.1 Sentinel-1 and Sentinel-2 Imageries  
Sentinel-1 and Sentinel-2 are free and publicly accessible imageries on GEE with the used band information shown in Table 1. The Sentinel-1 mission provides data from a dual-polarization C-band synthetic aperture radar (SAR) instrument at 5.405 GHz (C band). This collection includes the S1 ground range detected (GRD) scenes, which were calibrated and ortho-corrected in the Google Earth Engine (data available at: [[https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S1_GRD](https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S1_GRD)]([https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S1_GRD](https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S1_GRD)), accessed on 21 July 2022). The Sentinel-2 is a wide-swath, high-resolution, multi-spectral imaging mission supporting Copernicus land monitoring studies. A single Sentinel satellite revisits every 10 days, while the dual satellite constellations revisit every 5 days. The multispectral instrument (MSI)supports high-temporal-resolution data (data available at: [[https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S2_SR_HARMONIZED?hl=en](https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S2_SR_HARMONIZED?hl=en)]([https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S2_SR_HARMONIZED?hl=en](https://developers.google.com/earth-engine/datasets/catalog/COPERNICUS_S2_SR_HARMONIZED?hl=en)), accessed on 21 July 2022).  
In this study, a total of 404 Sentinel-2 images with less than 85% cloud coverage were used, as well as 371 Sentinel-1 images, with dates ranging from 1 January 2019 to 31 December 2021. For Sentinel-1 imagery, the vertical transmit/horizontal receive (VH) and vertical  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Satellite** & **Bands** & **Descriptions** & **Resolution (d/m)** \\ \hline Sentinel-1 & IW-VV & 5.405 GHz & 6/10 \\ \hline \multirow{4}{*}{Sentinel-2} & Band 2—Blue & 496.6 (A)/492.1 (B) & \multirow{4}{*}{5/10} \\  & Band 3—Green & 560 (A)/559 (B) & \\ \cline{1-1}  & Band 4—Red & 664.5 (A)/665 (B) & \\ \cline{1-1}  & Band 8—NIR & 835.1 (A)/833 (B) & \\ \cline{1-1} \cline{2-4}  & Band 12—SWIR2 & 2202.4 (A)/2185.7 (B) & \multirow{4}{*}{5/20} \\  & SLC & Scene classification map & \\ \cline{1-1}  & MSK\_CLDPRB & Cloud probability map & \\ \cline{1-1} \cline{2-4}  & MSK\_SNWPRB & Snow probability map & 5/10 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Band information of Sentinel-1 and Sentinel-2.  
Figure 1: (**a**) The location of the study areas in China; (**b**) the location of the study areas in Sichuan provinces; (**c**) the location of the study areas in Guangzhou city; (**d**) NASA SRTM digital elevation 30 m; (**e**) reclass map of GLC_FCS30 in 2020.  
transmit/vertical receive (VV) bands were considered, which are widely used for classification [41; 42]. For Sentinel-2 imagery, the SWIR2 band with 20 m resolution was resampled to 10 m with the nearest neighbor resampling method to match the blue/green/red/NIR bands. The bands of SLC, MSK_CLDPRB, and MSK_SNWPRB were utilized to remove distractions from clouds and shadows (Section 2.3.2).