Study on Phenology Character of Winter Wheat by Modis-Evi Data in Hebei China

Phenology is widely used in field management and output forecasting during crop growing period. Winter wheat is one of the most important crops in Heibei China and its phenology is affected by not only climate but also farmers´ planting habit. In this paper, time series of MYD09A1 in 2005 provided by NASA were used to calculate enhanced vegetation index (EVI). Based on winter wheat´s whole growing stages, three key phenologies were defined from temporal series EVI. The 16th 8d EVI image was used to show different growing conditions. From the south part of winter wheat area to the north in Hebei China, five areas of interesting (AOI) with the same EVI level were analyzed, and greenup, heading stage and maturity were derived from the images. Results show that EVI could be used to estimate phenology successfully. From south to north, with the increasing of latitude, greenup, heading stage and maturity of winter wheat in Hebei China became later and later. Winter wheat in the south turned green at the 8th 8d (about the first ten days in March), the middle part of winter wheat turned green about in the second ten days in March, which was 8 days later than that in the south, and the north part of winter wheat´s greenup was deferred about 8 days than the middle part. Periods among the three key phenologies of winter wheat were almost stationary and phenology of wheat in the south could be 8-16 days earlier than that in the north.