Based on the daily MODIS data under clear sky condition from March to November 2011 in Chongqing, authors computed the 10 -day (monthly,yearly) NDVI by using MVC method. The serial NDVI enlarged 100 times in different period of time were divided into 6 characteristic districts with different altitudes which were below 400m,400 -800m,800 - 1200m, 1200 - 1500m, 1500 -2000m and above 2000m and 5 characteristic districts with different slopes which were below 5 °, 5 ° -15 °, 15 ° - 25 °, 25 ° - 35 ° and above 35 °, and the NDVI of each district was analyzed . The results showed that (1) The NDVI augmented with the increase of altitude or lope. NDVI in districts below 1500m increased conspicuously and the added value was 3. 5 to 8. 7 between neighboring districts, but in districts above 1500m increased inconspicuously and the added value was < 1. 9 between neighboring districts. NDVI in districts below 25° increased conspicuously and the added value was 3. 0 to 8. 0,but in the districts above 25° increased inconspicuously and the added value was 0. 2 to 1.0. (2 ) According to analysis, in higher districts, the grid frequency of NDVI abovernthe average augmented with the increase of altitude. The correlation coefficient between NDVI and altitude was 0. 9552 ( P < 0. 01) while that between NDVI and slope was - 0. 3000. The results showed that the grid frequency of NDVI a-bove the average augmented with increase of altitude while there was no significant correlation between grid frequency of NDVI above the average and slope. (3 ) The difference of NDVI in different districts was reflected more conspicuously by altitude division than by slope division. The correlation coefficient was more than 0. 9541 between NDVI and altitude ( P < 0. 001) ,and was 0. 9457 -0. 9723 between NDVI and slope (P <0. 01). All the results above showed that in Chongqing city, the topographic factors had obvious effect on NDVI, and the effect of altitude on NDVI was more conspicuously than that of slope.%利用重庆市2011年3-11月晴空条件下逐日MODIS数据,采用最大值合成法合成逐旬(月、年)归一化植被指数,将各旬植被指数按高度和坡度分别分成6个高度特征区和5个坡度特征区,对各特征区植被指数进行对比分析.结果表明,(1)区域平均植被指数随特征区高度或坡度值增加呈增大的趋势.高程1500m以下相邻区域间NDVI值相差3.5 ～8.7,且植被指数随高度升高增加较快,1500m以上相邻区域间NDVI值相差在1.9以内,随高度升高增加缓慢；坡度25°以下相邻区域间NDVI值相差3.0 ～8.0,且植被指数随坡度增加增大较快,25°以上相邻区域间NDVI相差0.2 ～1.0,随坡度增大增加缓慢.(2)大于平均植被指数的频率与高度和坡度的相关分析表明,在海拔较高的特征区,植被指数高值格点的频率也较大,该频率与海拔高度间呈极显著正相关关系,相关系数为0.9552(P ＜0.01)；而植被指数与坡度无显著的相关性,相关系数为-0.3000.(3)按高度分区比按坡度分区更能体现植被指数的地区差异性.各高度特征区高程与植被指数的相关系数在0.9541～0.9871(P＜0.001),各坡度特征区坡度与植被指数的相关系数在0.9457 ～0.9723(P ＜0.01).研究结果说明,重庆市地形因素对植被指数有较大的影响,且高度因素对植被指数及其分布的影响较坡度更明显.
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