中文摘要：

利用中亚北部额尔齐斯河流域2000—2008年的中分辨率成像光谱仪（Moderate Resolution Imaging Spectrometer，MODIS）数据，分析了额尔齐斯河中亚段不同区域的归一化植被指数（Normalized Difference Vegetation Index，NDVI）随季节变化的规律，并合成全年最大NDVI值代表当年植被最好时期的NDVI值，应用混合像元分解模型，计算研究区内的植被覆盖度并根据植被覆盖度的高低将研究区内的植被覆盖程度分为六个等级：无覆盖、极低覆盖度、低覆盖度、中覆盖度、中高覆盖度和高覆盖度。通过研究区内植被覆盖度的变化情况在一定程度上揭示研究区内植被变化情况。2000—2003年，研究区的植被覆盖水平有降低趋势，2003—2007年呈增加趋势，2007覆盖水平与2002年相近，2008年覆盖水平降低明显，为9a来最低，是由研究区当年降水量减少引起；植被覆盖水平高的区域主要分布在研究区东北部的山区和西北部的平原区，植被覆盖水平较低的区域集中在流域中西部的干旱草原；高覆盖区域的植被覆盖年际变化幅度较中低覆盖区域的小。

英文摘要：

In this paper, the MODIS 500 m data of the Irtysh River basin of Central Asia from 2000 to 2008 was used to analyze the NDVI＇s seasonal variation regularities of the regions with different vegetation cover degrees. The annually largest value of NDVI obtained with synthesis method was represented as the NDVI value of vegetation in the best period of the year. The mixed-pixel decomposition model was applied to calculate the vegetation cover grades of the study area. According to their magnitude, the vegetation cover grades were divided into five levels ： no vegetation cover, extremely low vegetation cover, low vegetation cover, media vegetation cover, superior vegetation cover and extremely high vegetation cover. The results show that the vegetation cover grades of the research area were reduced from 2000 to 2003, and became rising from 2003. The 2007 vegetation cover grade was nearly as the same as 2002 ＇s. The 2008 vegetation cover grade was reduced too much and it was the lowest in the nine years. The region with high vegetation cover grade distributed in the mountainous area with flourishing forest in its northeast and in the plain in its northwest, while the region with low vegetation cover grade distributed in the arid grassland in its middle. The inter-annual variation of the vegetation cover grade in the low vegetation grade area is more obvious than that in the high vegetation grade area.