Spatio-temporal variations in cropland phenology in North China over the past 20 years

AVHRR NDVI time-series datasets were used to investigate the variations in the key phenology events in cropland of North China over the past 20 years. The method based on Savizky-Golay filter was used to reconstruct NDVI time-series data set, and reduce the effects time-series of cloud contamination and the Bidirectional Reflectance Distribution Function (BRDF). Based on NOAA / AVHRR NDVI 10-day time-series data, we estimated that the growing season duration of summer maturing crop has lengthened, primarily through an earlier onset date of the start of the growing season (SGS) and a later onset date of the end of the growing season (EGS) during period of 1982-2000 in north China. The autumn maturing crop has not showed the seminar characterization in area with double crop system. The onset date of SGS is earlier, and the onset date of EGS has slightly delayed in area with one crop system.