Land Cover Classification System Based on Spectrum in Poyang Lake Basin

In this paper, a new land cover classification system has been built according to the following ideas. Firstly, the formation of "Land Cover" has far-reaching geographic and biologic background, but global environmental change research and remote sensing give it new connotations. Land cover mainly represents morphological property and dynamic characteristics of the earth's surface. Vegetation is the primary component of land cover, but not only one. The functional properties of land cover, such as reflectivity, hydrothermal flux and net emissions of CO2 vary with different components and structures of covers. Secondly, spectral response and characteristics of seasonal variability are the fundamental characteristics of land cover. According to the difference in spectrum, it is easy to distinguish green land cover(mainly vegetation), blue land cover (mainly water), grey land cover (mainly urban or built-up land, and semi-desert), white land cover (mainly snow and ice), non-vegetated land cover(mainly desert), etc. Similarly, characteristics of land-cover's seasonal variability derived from remote sensing images can make some typical land cover easy to be distinguished further, such as evergreen land cover has high NDVI index and no remarkable change in a year, deciduous forest single peak of NDVI sliding curve in a year, annual double crops double peaks, and annual triple crops triple peaks. Therefore, we can make the classification criteria quantified with the characteristic values indicated by NDVI including greenness value, green-up period, green-end period, crest value, trough value and waveform of NDVI sliding curve in a year, etc. Moreover, mixed cover should be differentiated by its structural characteristics and functional properties.Based on these ideas, a two-level land cover classification system has been proposed for the clustering of Poyang lake basin's land cover by using multi-temporal SPOT4-VEGETATION sensor data. The primary types include Evergreen Cover, Seasonal Green Cover I (Woody), Seasonal Green Cover II (Herbaceous), Seasonal Green Cover III (Crops), Seasonal Green Cover IV (Mixed), Grey Cover and Blue Cover. The secondary level includes 20 types. According to area proportion, the main land-cover types in Poyang lake basin are evergreen cover (40.05%), crop-forest-grassland mixed cover (38.29%), and crops (16.63%) at present.