In this paper, the normalized difference vegetation index (NDVI) was calculated based on the TM satellite image data taken in June, 1995 and June, 2009, and was in turn used to estimate vegetation coverage in Xi'an city. The vegetation change was quantitatively assessed with the NDVI when the vegetation coverage was more than 0. 1. The result showed that the vegetation situation was improved. In 1995, the average value of NDVI was 0.252 2, but in 2009, the value reached 0. 388 2. The highest NDVI was in mountain area and the ecotone region between the mountain and the plain, while the lowest NDVI was in plain region because the crops were just harvested by then. From 1995 to 2009, the area with extreme low, low and high vegetation coverage reduced by 1. 05, 22. 25 and 1. 81 percentage, respectively, and the area with the medium and extreme high coverage increased by 12. 68 and 12. 43 percentage. The difference value index of NDVI indicated that the moderate and extraordinary amelioration area were occupied 86. 81% of total area. The degraded area only occupied 5. 58% , and mainly distributed in the Xi' an districts, the highest peak in a Taibai mountain range and the northern part of ecotone area between Zhouzhi County and Huxian County. The amelioration area was mainly distributed in the ecotone area among Qinling Mountain and Guanzhong plain, Heihe river valley, Lishan mountain and the plain part of Zhouzhi County. The driving forces of the vegetation change would include the implementation of natural forest protection and grain for green in the mountain, orchard development, new village construction, as well as the greening in the city.%利用1995年6月和2009年6月的TM卫星影像数据,计算西安市同期的归一化植被指数(NDVI),并以此为基础,反演植被覆盖度,通过植被覆盖度大于0.1的归一化植被指数的差值分级,量化分析西安市1995-2009年的植被状况.结果表明:西安市NDVI均值从1995年的0.252 2提高到了2009年的0.388 2,山区与前山缓坡带NDVI高,平原区受夏收刚过的耕地裸露的影响,NDVI低;从1995年到2009年,极低覆盖度、低覆盖度和高覆盖度植被的面积均有所减少,占全市土地面积的比例分别降低了1.05％和22.25％和1.81％,而中覆盖度和极高覆盖度植被的土地面积分别增加了12.68％和12.43％;NDVI差值指数统计结果显示,无论是全市还是各地势分区,均以中度改善和极度改善的面积为主体,市域内二者合计面积占到了全市有植被覆盖土地面积的86.81％,而全市域植被退化面积仅占全市有植被覆盖土地面积的5.57％;生态退化区域主要分布在市区、户县与周至县行政边界交汇区的北部区域和山区太白山主峰一带,生态极度改善区域主要分布在山区与关中平原区的交错带一线、周至县的黑河河谷、地跨临潼区与蓝田县的骊山山区和周至县的平原区等地.
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