利用2001--2009年5—10月EOS／MODIS数据，分析延安北部七县区退耕还林（草）生态建设工程实施以来植被指数变化。结论表明：延安北部归一化植被指数NDVI整体上呈上升趋势，线性趋势为0．0153，平均增加了0．16，最多的增加0．19，最低的也提高了0．14，增幅比较均匀。2009年与2001年NDVI差值在0．12以上的比例达88．6％，0．2以上所占比例为13．5％。延安植被覆盖度从2001年的35．3％增加到2009年的55．8％，增加了20个百分点，线性增长趋势为1．9917，变化极为显著。叶面积指数由2001年的0．66增加到2009年的1．18，增加了近一倍。遥感监测图上延安北部植被指数明显高于周边地区，行政边界轮廓明显凸现。退耕还林后延安植被发生了明显变化。%By using the EOS/MODIS temporal series data from May to October during the period of 2001-2009,this study examines the vegetation cover change in the seven counties/districts of northern Yan＇an since the implementation of ecological construction of returning the farmland to forestland/grassland. Form the above analysis,we can draw the conclusion that： （1）The NDVI in northern Yah＇an shows an upward trend generally with the linear trend of 0.0153,increasing by 0.16 in average, and ranging from 0.14 to 0.19,and the increase represents uniformity. The difference of NDVI between 2009 and 2001 is 0.12 above in the proportion of 88.61% ,and 0.2 above in the proportion of 13.51%.（2）The vegetation coverage in Yah＇an has increased by 20% from 2001 （35.3%） to 2009 （55.8%）,and the linear growth trend reaches 1.9917,representing a significant change; the LAI （leaf area index） has nearly doubled from 2001 （0.66） to 2009 （1.18）. （3）The NDVI in northern Yah＇an is obviously higher than surrounding areas in the remote sensing monitoring map, clearly highlighting the administrative boundary counter. Conclusively, the vegetation cover in northern Yan＇an has occurred significant changes after returning farmland to forestland.
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