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为了明确太湖不同生态区水生植被长势的变化规律及其影响因子,利用MODIS传感器提供的NDVI数据,分析了太湖2000年—2015年NDVI的时间及空间变化特征。结果表明:太湖水生植被NDVI存在明显的季节变化和年际变化,NDVI每年最小值出现在冬季,最大值出现在植被生长旺盛的8月或9月,其值可达0.35;太湖全湖NDVI多年平均值为0.1,最大值为0.14,出现在2007年。太湖NDVI的空间差异可将太湖划分为不同的植被类型区,太湖西北部(竺山湾和梅梁湾)NDVI最大值可达0.2,植被类型主要以浮游藻类为主,东太湖区域最大值超过0.6,主要以沉水植被为主;太湖不同区域植被动态特征对气象因子的响应也不尽相同,沉水植物生长与平均气温有显著的正相关关系,而浮游植物区的生长状况受平均风速影响较大。
The temporal and spatial variations in the Normalized Difference Vegetation Index (NDVI) were analyzed and the factors that affect the growth condition of different types of vegetation in Lake Taihu were identified using MODIS NDVI data gathered from 2000 to 2015. MOD13Q1 data were obtained with 16-day temporal resolution and 250 m spatial resolution. Projection transformation and irregular cutting were implemented according to the vector diagram of Lake Taihu. Then, abnormal values were eliminated by the band math module of ENVI 4.7 software (The range of NDVI is between -0.2 and 1). We analyzed the corresponding NDVI values and imported the results to MATLAB R2015b software according to the latitude and longitude that determine corresponding pixel points. The result indicated seasonal and inter-annual variations in the NDVI of aquatic vegetation in Lake Taihu. Annual minimum NDVI occurred in winter, and the maximum in August or September, reaching 0.35 with flourishing vegetation growth. The multi-year mean NDVI was 0.1, and the annual mean NDVI was the largest in 2007 at 0.14. The spatial distribution of NDVI and the different types of vegetation can be distinguished in Lake Taihu. The northwestern area of the lake (Zhushan Bay and Meiliang Bay) was covered by planktonic algae; the maximum value was larger than 0.2 in this area. The east area was mainly covered by submerged vegetation; the maximum value exceeded 0.6 in this region. In the different ecological areas of Lake Taihu, the responses of vegetation growth to meteorological factors differed. The seasonal NDVI variation of Lake Taihu was of single-peak type. The growth season of aquatic vegetation was from April to November. The inter-annual variability of spatial distribution of NDVI in the planktonic algae area could reflect the dynamics of cyanobacteria distribution. Submerged vegetation growth was positively correlated with mean air temperature. However, wind speed affected the growth of the planktonic algae.