CropWatch: Cropped arable land fraction

Cropped arable land fraction (CALF) was introduced to demonstrate the proportion of cropped arable land to the total arable land over a certain geographic area (Major Production Zones (MPZs), countries or sub-national units). Monitoring the dynamic changes in arable land utilization, specifically the dynamic identification of cropped and uncropped arable land, is important. CALF can reflect the rotation pattern of different crops and the change of cultivated land planting intensity, especially for early warning of crop planting area. On the basis of an analysis of profiles of time series NDVI, Savitzky-Golay filters are used to smooth the noise in NDVI curves, and Lagrange polynomials are employed to extract the extreme points for the smoothed NDVI curves. A threshold method associated with NDVI curve analysis is used to identify dynamic changes in the distribution of cropped and uncropped arable land. CALF over those regions was then calculated based on cropped and uncropped map and zonal statistical analysis.