REMOTE SENSING OF THE SEASONAL NAKED CROPLANDS USING SERIES OF NDVI IMAGES AND PHENOLOGICAL FEATURE

Naked cropland elimination is an important part of Beijing Olympic ecological project. In this paper, Multi-temporal satellite data were used to monitor and position the naked croplands. Three Landsat TM images and two "Beijing-1" Small-Satellite images were selected to calculate NDVI series according to crop phenological calendars and investigated information of agricultural cropping structures in Beijing suburb. Based on the phenological spectral characteristics of main agricultural land use types, a classification scheme was proposed to extract the naked croplands. Considering the structural characteristic hierarchical classification and various demands of feature selection in different periods, decision tree algorithm and a stepwise masking technology were employed to extract typical crops in each season, and hence the naked croplands were left. Accuracy assessment of the naked croplands in winter and spring were performed with comparison of the monitoring areas with statistical data. The results show that the area of the naked croplands in winter and spring was 170368.1ha in Beijing. The areas of the top five districts (Yanqing, Shunyi, Daxing, Miyun and Tongxian) were 17933.3ha, taking a percent of 69.2% of that of Beijing. The areas of the naked cropland were 25719.6 ha, 4485.4 ha and 3325 ha in summer, autumn and all the year round respectively. Experimental results demonstrated that our method would fast and simply monitor agricultural land use.