城市热岛研究中地表温度与植被丰度的耦合关系

城市热岛遥感研究传统上应用归一化植被指数(Norm alized D ifference Vegetation Index,NDVI)作为植被丰度(vegetation abundance)的指示,并用于耦合地表温度与植被之间的关系.文章探讨了运用光谱混合模型获得的植被比例(vegetation fraction)作为植被丰度指标的一种选择,以2000年9月14日获得的122/44景ETM 截取的广州市海珠区作为验证影像,运用最小二乘法将变换的影像分解成三个分维影像,即绿色植被、非渗透性表面和水体.结合最大似然分类和决策树算法的混合分类处理,将比例影像进行土地覆盖分类.结果表明,地表温度与分解的植被比例的负相关关系比地表温度与NDVI的负相关关系要高出几分.由此说明,地表温度结构的空间变异无疑与归一化植被指数和植被比例相关,不同土地覆盖类型的热辐射与植被动态的相互影响导致地表温度在光谱辐射率和结构上的变化,这些变化在别的影像中也有表现,这是城市热岛空间格局形成的原因.

Coupling relationship of land surface temperature-vegetation abundance for urban heat island studies

Remote sensing of urban heat islands(UHIs) has traditionally used the Normalized Difference Vegetation Index(NDVI) as the indicator of vegetation abundance to estimate the land surface temperature(LST)-vegetation relationship.This study investigated the applicability of vegetation fraction derived from a spectral mixture model as an alternative indicator of vegetation abundance.This is based on examination of a Landsat Enhanced Thematic Mapper Plus(ETM ) image of Haizhu district,Guangzhou City,acquired on September 14,2000.The transformed ETM image was unmixed into three fraction images(green vegetation,impervious surface,and water) with a constrained least-square solution.These fraction images were then used for land cover classification based on a hybrid classification procedure that combined maximum likelihood and decision tree algorithms.The results showed that LST possessed a slightly stronger negative correlation with the unmixed vegetation fraction than with NDVI for all land cover types.The spatial variability of texture in LST was positively correlated with those in NDVI and in vegetation fraction.The interplay between thermal and vegetation dynamics in the context of different land cover types leads to the variations in spectral radiance and texture in LST.These variations are also present in the other imagery,and are responsible for the spatial patterns of urban heat islands.