城市热场剖面的分形维数计算及其意义研究——以上海中心城区为例

城市热环境是城市中建筑物的不断增加及人类活动、大气状况、地表热量传输等多种因素综合作用的结果，因此城市往往具有极为复杂的热表面。由于热量分配、传输具有一定的复杂性，传统的模型预测与定点观测方法在分析城市热表面空间结构及其形成机制方面存在一定的不足。随着空间信息科学的发展，卫星遥感技术为获取城市热场信息提供了可靠的手段。选用上海市2000年6月14日的Landsat ETM+热波段影像，首先反演城市地表温度，再引入剖面线分形的方法，在GIS的支持下，计算从人民广场出发的8个方向的分维数，并进一步探讨剖面线分形的意义，得到如下结论：城市热表面的剖面线具有明显的分形特征，8个方向的分维数为1.530 0～1.780 6，表征不同剖面线的复杂程度。热场表面剖面线的分维数揭示了3个方面的意义：首先不同的分维数反映热场不同方向上温度变化的复杂程度；其次，相对于城市中心，反映不同方向上城市边界形态的差异性；第三，进一步揭示不同方向上，下垫面土地利用类型空间组合变化的复杂程度。

CALCULATION OF PROFILE LINE FRACTAL DIMENSION FOR URBAN THERMAL SURFACE

The urban thermal environment is dependent strongly on human activities,atmospheric condition and heat transmission etc,which make the urban thermal surface rather complex.As the heat distribution and transmission differ in various land covers,the traditional method such as providing model for forecasting or setting spots to observe variations is not enough to describe the structural and potential factors of thermal environment.It is also found out that the radiation geometry and the properties of the surfaces contribute more to thermal phenomenon.With the development of the spatial geosciences,remote sensing technique is used well to study urban environment.In order to reveal the thermal properties of the surfaces and the urban heat island(UHI) in Shanghai,China,land surface temperature was derived from Landsat ETM thermal infrared image dated on 14th June 2000.Considering the spatial distribution of land surface temperature as "thermal surface",the fractal dimension was computed through profile line fractal method in eight directions.It is revealed that there is an evident fractal character for urban thermal surface profiles.The fractal dimensions in eight directions are between 1.530 0 and 1.780 6,which reveal the complexity of different thermal profiles.By analyzing the factors to UHI,thermal fractal characters are mainly due to the scope and shape of built-up area and land surface properties.