# High-Precision Tea Plantation Mapping with Multi-Source Remote Sensing and Deep Learning
## 2 Study Area and Data
### Data
#### 2.2.1 Sentinel-2 Imagery  
This study utilizes Sentinel-2 imagery (Figure 2) as the optical data source. Sentinel-2, launched by the European Space Agency (ESA), is a high-resolution multispectral imaging satellite constellation consisting of Sentinel-2A and Sentinel-2B. Each satellite has a revisit period of 10 days, while the combined revisit period of both satellites is only 5 days [28]. Equipped with a multi-spectral instrument (MSI), Sentinel-2 covers a total of 13 spectral bands, including aerosol, visible, red-edge, near-infrared, and shortwave infrared bands [29]. Ten bands with resolutions of 10 m and 20 m were selected for this study (see Table 1 for selected band information). Sentinel-2 satellite data are available in three levels: Level-0, Level-1C, and Level-2A, with Level-2A images representing surface reflectance data after atmospheric correction [30]. This study utilized Level-2A Sentinel-2 imagery covering the study area for the year 2019. Due to issues such as cloud cover, only six cloud-free Sentinel-2 images covering the study area for the entire year of 2019 were acquired in May, June, August, October, November, and December (see Figure 3). In addition, this study acquired complete Sentinel-2 time-series normalized difference vegetation index (NDVI) curves (Figure 3) from the cloud-free areas of all Sentinel-2 images covering the study area in 2019. From Figure 3, it can be observed that after the spring tea picking period, the NDVI values of Anji white tea sharply decrease. This is mainly due to the deep pruning technique adopted for Anji white tea, which involves the complete removal of upper branches and leaves from the tea plants (Figure 3). This period is also a critical phenological stage for the remote sensing identification of Anji white tea. As indicated by the blue area in Figure 3,  
Figure 1: The geographical location and elevation of the study area. The background is the digital elevation model (DEM) of the Anji area derived from NASA’s Shuttle Radar Topography Mission (SRTM). (**a**) Zhejiang Province; (**b**) Huzhou City; (**c**) Anji County.  
there were only two Sentinel-2 satellite images acquired during this critical phenological stage (obtained respectively in early June and early August), posing challenges for the identification of Anji white tea based on optical imagery. The study employed Sentinel-2 Level-2A surface reflectance products, with Google Earth Engine utilized as the platform for acquiring and preprocessing Sentinel-2 data. The image resolution was uniformly resampled to 10 m.  
Figure 3: The acquisition dates of Sentinel-2 (S2) and Sentinel-1 (S1) satellite images in the study area, as well as the time series NDVI curves of tea plantations (**c**). The time series NDVI curves of tea plantations were derived from Sentinel-2 images of tea gardens within the study area that were not obscured by clouds in 2019. Blue area represents the period of NDVI decrease and recovery caused by intensive pruning of Anji white tea plants. (**a,b**) were taken on-site at tea gardens during the period indicated by the arrows.  
Figure 2: Anji Sentinel-2 satellite imagery (**a**) and its zoomed-in section (**b**). The images were acquired on 3 June 2019, using bands B8 (near-infrared), B4 (red), and B3 (green) for false-color composite, representing red, green, and blue, respectively.