Using NDVI and Air Temperature to Monitoring Winter-Wheat Phenology in Xingtai, Hebei, China

The Normalized Difference Vegetation Index can accurately reflect the phenology changes of a wide range of crop areas. This paper discusses the monitoring methods of returning green and heading stages of winter wheat. Xingtai in the southern Hebei in China is selected as the study area and it uses SPOT / VEGETATION Maximum Value Composite (MVC) NDVI data in period of ten days to analyze relevance of MVC NDVI and the highest temperature of the same period. Then it makes the MVC NDVI data to date with the highest air temperature, and reconstructs the NDVI time series data during the growing season of winter wheat. The NDVI curve is fitted by the asymmetric Gaussian model, and green-turning and heading stages of winter wheat are extracted by dynamic threshold method. At the same time, it makes the MVC NDVI to the middle and end of every period of ten days, and then follows the same method to extract the same phenology phases. Finally, the paper makes a comparative analysis about these methods referred above based on the field observation data. This analysis indicates that there is a significant correlation between MVC NDVI and the highest air temperature of the same period for the winter wheat in the research area. Monitoring accuracy of the starting day of returning green and heading stages can be improved by the NDVI curve combined with the highest air temperature.