利用Landsat ETM+分析城市热岛与下垫面的空间分布关系

采用数理统计与空间统计相结合的方法,利用Landsat ETM 数据对北京、上海、沈阳和武汉等4个大城市的夏季城市热岛相对强度与城市下垫面的空间分布关系进行对比研究。用混合像元线性光谱分解方法提取的城市植被覆盖度与不透水面表征城市下垫面;用城市地表亮温与水体亮温差值表征城市热岛相对强度。结果显示,4个城市的植被覆盖、不透水面与热岛强度的分布呈较强的空间正自相关,并且存在较为一致的自相关范围,该范围相当于城市街道与建筑组合特征尺度;自相关引起的结构性是导致3者空间分布异质性的主要因素。植被覆盖对城市热岛的缓解效果与不透水面对城市热岛的增强作用均呈分段线性特征,但区域差异较为明显;交叉相关系数曲线则显示出相关性的空间异质性与多尺度现象,同时存在一个约550 m的空间作用特征尺度。该研究结果有助于在城市规划实践中合理配置建筑与植被的间隔和比例,以缓解城市热岛效应。

A SPATIAL ANALYSIS OF URBAN HEAT ISLAND AND UNDERLYING SURFACE USING LANDSAT ETM+

The relationship between urban heat island and underlying surface was analyzed for the first time in Beijing,Shanghai,Shenyang and Wuhan in summer based on Landsat ETM data by combining mathematical statistics with spatial statistics.The urban underlying surface was represented by green vegetation and impervious surface generated by a linear spectral mixture analysis,while the relative urban heat island strength was represented by difference of radiant brightness temperature between surface and water.Radiant brightness temperature was retrieved from the thermal band.Results obtained in these cities suggest that a positive spatial autocorrelation exists in the distribution of green vegetation,impervious surface and heat island strength,with the existence of a similar autocorrelation range equivalent to the spatial pattern character of the combination of buildings and roads.As a result of spatial autocorrelation,the structural factor is more important than the random factor in contributing to spatial heterogeneity of urban green vegetation,impervious surface and heat island strength.Statistics show that the positive relationship between impervious surface and heat island strength exhibits different nonlinear characteristics in these four cities,which can be expressed by piecewise functions according to the quantity of impervious surface,and things are quite similar for the negative relationship between green vegetation and heat island strength.In these four cities,both the positive and the negative relationships demonstrate spatial heterogeneity and multi-scale character,along with an obvious spatial scale proximate to 550 meters detected by using cross-correlation.These conclusions may provide some ideas for civil planning,i.e.,through designing of reasonable intervals and proportions between green vegetation zones and buildings,the effect of urban heat island can be weakened.