Strategy to extract winter wheat and summer maize distribution based on time-serie MODIS NDVI data

Crop plantation map is a fundamental data in the research and production of agriculture. Remote sensing is a fast, economic and irreplaceable tool in this research and application area. By the analysis of the penology of winter wheat and summer maize using the data from agro-meteorological station and the characteristics analysis of the 8-day time-series MODIS NDVI of winter wheat and summer maize, this paper proposed a model to extract the distribution of winter wheat and summer maize based on NDVI apex and valley characters. The threshold of winter wheat at county level in the model was derived with the density cutting method using the agricultural statistical data of planting area and MODIS NDVI data. The relationship between threshold and latitude was proposed, which reflects the controlling role of latitude to temperature and crop growth. Then, the threshold of winter wheat at the pixel level was estimated using the above-mentioned relationship. Using this threshold, we get the distribution of winter wheat. The accuracy evaluation using 90 stations showed that the overall areal resolution is about 91.15% and the accuracy at county scale is averaged as 67.52%. The distribution of summer maize was extracted using the threshold at county level. The distribution map demonstrated that the coverage of winter wheat and summer maize were affected by the growing condition at local region. Most of them appeared at plain, but less of them distributed at the region with bad condition such as rugged and salt-affected seaside area. In the yanshan and taihangshan mountainous area, the land surface is rugged with high slope, thin soil and poor irrigation condition. So, the amount of crops is limited in this area. Otherwise, in the plain area before the mountain area and the lower plain the winter wheat and summer maize were widely planted with percentage more than 60%. Lastly, in the coastal area near bohai gulf which was affected by salt, the crops were rare in distribution.