## 2 Study Area and Datasets
### The Zhaosu Study Area  
The second study area is Zhaosu, situated southwest of Yining City, Xinjiang Autonomous Region, China (latitude range: 43\({}^{\circ}\)09\({}^{\prime}\)N to 43\({}^{\circ}\)15\({}^{\prime}\)N and longitude range: 80\({}^{\circ}\)08\({}^{\prime}\)E to 81\({}^{\circ}\)30\({}^{\prime}\)E in geographical coordinates) (Figure 2). It is a highland basin surrounded by mountains in the Central Asian hinterland, with an elevation ranging from 1323 m to 6995 m. It is dominated by a continental temperate semi-arid semi-humid cool climate, with an annual average temperature of 2.9 \({}^{\circ}\)C and 512 mm of annual precipitation. The majority of Zhaosu is covered by calcium-rich black soil with a thick humus layer and a high organic matter content. These natural geographical and climatic conditions are optimal for the growth of spring rapeseed (from April to September), making Zhaosu the largest producer of spring rapeseed in Xinjiang.  
Official farmland parcel maps are unavailable for this study. Consequently, Chinese Gaofen-1 (GF-1) satellite images were used to delineate the precise geometries of farmland parcels. The GF-1 images included one panchromatic band with a 2 m spatial resolution and four multi-spectral bands (blue, green, red, and near-infrared) with an 8 m spatial resolution. Using the Gram-Schmidt spectral sharpening algorithm, the panchromatic and multi-spectral bands were combined to produce a multi-spectral pan-sharpened image with a 2 m spatial resolution. Two GF-1 images acquired in July 2020 with 60 km-wide swaths were registered and mosaicked to cover the study area. In this study, approximately 11,400 parcels were obtained.  
In July 2020, field surveys for supervised crop classification and accuracy assessments were conducted. To facilitate the field surveys, sample sites were distributed along the roads. In surveys, a handheld GPS device (with a precise point positioning precision level  
Figure 2: The Zhaosu study area is located in Xinjiang’s northwestern region. The center section provides an overview of the Sentinel-2 image acquired on the DOY 190 in 2020 (with the true-color composition). The top left corner presents local details of parcel geometry.  
of 3.0 m) was utilized to record geographic location (in the WGS84 geographic coordinate system). Approximately 1000 parcel samples were collected (200 rapeseed parcels and 800 parcels with other crops, proportional to the percentage of rapeseed-planted area). Therefore, this study designed a binary classification schema containing rapeseed and other types.  
Two Sentinel-2 images (with P/R of T44 TMN and T44 TNN) captured on the same day were mosaiced to cover the Zhaosu study area. And 36 observations between April and September 2020 were used to identify rapeseed. Also, images acquired on DOY 115, 145, 165, 185, 190, 195, 220, 235, 255, 260, and 265 in 2020 were totally clean.  
The datasets and crop growth periods are summarized in Table 1. The two study areas were distinguished by distinct climatic and topographical conditions. In addition, the cultivation status of crops varied considerably based on crop type and farming technique. These circumstances were sufficient for validating the proposed model.