三江源区植被覆盖度的定量估算与动态变化研究

植被覆盖度是衡量地表植被状况的重要指标，其时空分布和变化对政府进行区域规划和决策起着重要作用。MODIS植被指数是区域植被覆盖度提取的重要数据源。利用2000年1月到2009年10月的MODIS 250 m归一化植被指数16 d合成产品（MODIS NDVI）和其他MODIS辅助数据估算三江源区的植被覆盖度并分析时空格局变化趋势。在混合像元二分模型的基础上改进了NDVI参数的确定方法，然后利用重构后的MODIS数据估算植被覆盖度。与2007年8月的野外采样点数据比较，估算精度是8772%，相关系数r为0889 7，表明该模型估算大面积植被覆盖度是可行的。将获得的植被覆盖度分为5个等级，从年最大化植被覆盖度Mfc的角度进行10 a里植被覆盖度的年际变化趋势分析和时空格局变化分析。趋势分析结果表明，2000~2009年三江源区植被覆盖波动式变化，东北部地区得到改善，西部地区在退化，总体呈现退化趋势；时空格局变化分析结果表明，植被覆盖破碎度降低，趋于集中化分布；不同等级覆盖度分布的复杂化程度降低

QUANTITATIVE ESTIMATION AND DYNAMIC CHANGES OF VEGETATION FRACTIONAL COVERAGE IN THE SANJIANGYUAN REGION

The Vegetation Fractional Coverage (VFC) is a fundamental parameter of climate and hydrologic models.The spatio temporal distribution and change of the VFC is important for future regional planning and governmental policy making.Moderate Resolution Imaging Spectroradiometer （MODIS） vegetation index (VI) is an important data to extract global and regional VFC.The objectives of this study are to explore the potential of quantitatively estimating the VFC using time series of MODIS 250 m Normalized Difference Vegetation Index (NDVI) 16 day data and other auxiliary MODIS data,and to monitor the spatio temporal patterns of the changes from 2000 to 2009 in the Sanjiangyuan Region.Under the assumption that each pixel of a MODIS image contains two NDVI end members:vegetation NDVI (NDVIveg) and bare soil NDVI (NDVIsoil),this paper improved the determination of parameters NDVIveg and NDVIsoil in the pixel unmixing model.Then based on the time series reconstruction of MODIS data,the VFC was quantitatively retrieved using different pixel unmixing models.The retrieval accuracy was assessed at 8872% and the correlation was 08897 for Aug.2007,which suggested this method might be generally useful for VFC estimation at broad spatial scales.The inter annual dynamic variability trends and the spatio temporal landscape patterns of change were characterized over the past ten years based on the year maximization vegetation fractional coverage (Mfc).The slope trend analysis and field investigation indicated that the change trend of vegetation was fluctuant and the VFC had been improved in the eastern part while worsened in the western part.The area of vegetation degradation was larger than that of vegetation improvement from 2000 to 2009.The patterns of change revealed that the coverage fragmentation had been decreasing and the complicated degree of the distribution of different grades had been reduced