Spatial sampling design for monitoring the area of cultivated land
Updated information on cultivated land is important for Chinese central and local governments. The data can be acquired using aerial photographs and Thematic Mapper (TM) images. But an exhaustive annual survey covering all of China's territory by these remote sensing images is too expensive, therefore a sampling technique has to be employed. Spatial sampling takes the spatial distribution characteristics of the object to be monitored into account. We propose both direct and indirect spatial sampling models for monitoring spatially discrete distributed objects. For the indirect method, each sampling domain is equal to a specified region but is not directly linked with the reporting unit, consequently, the report unit estimates may have few or perhaps even no samples within the report units. Therefore the indirect sampling model can provide sampling estimates for a large number of report units with a limited number of sample units and a limited sampling budget. The zoning of the monitored object is based on prior knowledge about the controlling factors and the spatial homogeneity of the variable. The method is used to develop a sampling solution for monitoring cultivated land dynamics. The models were tested in Shandon province and Zhaozhuang county.