基于遥感影像的城市土地利用生态环境效应研究——以城市热环境和植被指数为例

城市化过程中,农村的土壤、水面以及植被等土地覆被类型逐渐减少,取而代之的是由沥青、水泥以及金属等组成的不透水表面,这个过程导致地表水分蒸腾减少、径流加速、显热的存储和传输增加以及水质降低等一系列生态环境效应,其中最明显的两个特征就是土地覆被的植被减少、城市热岛的出现.而城市土地利用类型及其空间结构的生态环境效应同时又是城市生态学中的关键问题,其研究对优化城市功能分区和城市规划管理以及城市可持续发展等都具有重要意义.以上海市为例,采用Landsat7的ETM＋为基本数据源,首先定量反演了每个像元内的陆地表面温度（LST）和植被指数（NDVI）,然后利用GIS中的空间分析功能,将由于城市土地覆被所形成的生态环境效应综合到土地利用的图斑中来,按照这个思路对城市土地利用的生态环境效应进行研究.分析LST、NDVI在不同土地利用类型之间的差异以及二者之间的定量关系,并引入多样性指数（SHDI）,讨论了不同土地利用的空间组合下,LST和NDVI的空间差异及相互关系.研究结果显示：LST和NDVI具有明显的相关性,LST大的区域对应NDVI一般都较小,反之亦然;中心城市LST表现出热岛效应,而NDVI则为低谷效应.通过Tamhance T2 post-hoc多重比较发现,LST以及NDVI在两两土地利用类型之间的差异不同.从土地利用斑块和类型两种尺度水平上建立了LST和NDVI的定量关系,二者具有明显负相关的线性关系,但在不同土地利用类型上二者关系并不同.其中工业仓储、交通用地与公园绿地、农业用地差异最为显著.它们和SHDI之间的关系揭示,LST与土地利用多样性具有正相关关系,而NDVI则与SHDI呈负相关关系,SHDI越大的地区,LST越大,而NDVI越小.由此,可以将LST、NDVI和SHDI作为三个基本指标,来定量评价城市土地利用类型、结构对生态环境的影响,以此作为城市功能分区中生态环境影响评价的参考.也为高性价比的中等分辨率遥感数据与GIS空间分析方法结合在城市规划中的应用提供了一种新的思路.

An analysis on eco-environmental effect of urban land use based on remote sensing images:a case study of urban thermal environment and NDVI

In urbanization process, greater consideration of the manner in which rural lands are developed for urban lands will become progressively more important. Removal of rural land cover types such as soil, water, and vegetation and their replacement with common urban materials such as asphalt, concrete, and metal have significant environmental implications including reduction in evapotranspiration, promotion of more rapid surface runoff, increased storage and transfer of sensible heat, and reduction of air and water quality. Thermal environment and vegetation cover are two important factors for urban eco-environment. Land Surface Temperature (LST) and Normalized Difference Vegetation Index (NDVI) associated with urban land use type and land use pattern are discussed in this paper, using the data collected by the Landsat7 Enhanced Thematic Mapper Plus (ETM ) and aerial photography remote sensing system in the city of Shanghai. Analysis of variance indicates statistically significant differences in mean LST and NDVI values. Mean LST and NDVI values associated with different land use types are significantly different. There is an apparent correlativity between LST and NDVI from the profile line values of the two factors. Multiple comparisons of mean LST and NDVI values associated with pairings of each land use type by Tamhane's T2 post-hoc tests are also shown to be significantly different. The result of a regressive analysis shows a significant inverse correlation relationship between LST and NDVI associated with all land use polygons, the same associated with each land type, but correlation coefficients associated with land use types are different. Then an analysis was performed about the relationship among LST, NDVI and Shannon Diversity Index (SHDI), which shows a positive correlation between LST and SHDI and a negative correlation between NDVI and SHDI. As the SHDI continue to increase, it's more sensitive of LST change on the influence of NDVI.According to the above results, LST, SHDI and NDVI can be considered to be three basic indices to reflect urban eco-environmental effect of urban land use/cover and to contribute to further validation of the applicability of relatively low cost, moderate spatial resolution satellite imagery (TM or ETM ) in evaluating environmental impacts of urban land function zoning, then to examine the impact of urban land use/cover on the urban eco-environment in the city of Shanghai, China. And this paper also provides an effective tool in evaluating environmental influences of zoning in urban ecosystems with remote sensing and geographic information system. As higher resolution remote sensing imagery becomes more commonly available, the methods presented in this research could be extended to more specific urban design considerations that impact the thermal and vegetation components of urban ecosystems at finer spatial scales.