From cropland to cropped field: A robust algorithm for national-scale mapping by fusing time series of Sentinel-1 and Sentinel-2

•Automatic method developed for mapping actively cropped fields without regional adjustments.•Combined use of Sentinel-1 and Sentinel-2 increases mapping accuracy.•High performances in correctly labelling sparse crops and separating grass from cropped fields.•The first 20-m national-scale map of cropped fields and abandoned cropland generated in China.•Around 77% cropland are cropped with field crops in China at national scale.