2.1.1. Study Area

The study area was the North China Plain and the middle and lower reaches of the Yangtze River Valley (Figure 1). Major land-cover types were natural vegetation, croplands, water bodies and built-up areas. Forests and scrublands were synthesized to natural vegetation since they have similar phenology. Double-cropping and single-cropping coexist in the research area. The dominant crop patterns are single-cropping paddy rice, winter wheat-soybean, winter rapeseed-paddy rice, winter wheat-maize and double-cropping paddy rice.

**Figure 1.** The location, major land-cover types and reference samples of the study area (A and B are two test regions, corresponding to Sentinel-2 tiles 49RFP and 50SKC). The main land cover types are from the FROM-GLC10 datasets (data source: http://data.ess.tsinghua.edu.cn/, accessed on 1 March 2023) in 2017.
