城市热岛是指城市化过程中城区高空以及近地面大气温度高于城区以外郊区的现象。城市热岛强度是城市热场分布的重要表达手段，目前，对专门研究城市热岛强度的计算方法讨论较少。本文利用Landsat 5数据，基于遥感相关理论，以合肥市为例，反演出城市地表亮温，同时引入城市形态分维理论，使用改进的半径法对合肥市的城市热场状况进行研究，发现亮温的水平分布在城市建成区与非城市建成区间有突变现象，并以此分析城市热力场的空间分布，得到热岛强度计算公式，从而得出城市热岛强度的表达方式。在城市热岛强度计算过程中，着重考虑了城市热场分布特征，克服了在研究城市热岛时寻找郊区气温值的困惑，这对于城市热岛强度的表达研究具有一定的指导意义。

Urban heat island is a phenomenon related with the fact that the urban upper air temperature is higher than the surrounding area. The intensity of the urban heat island is an important index for the urban heat environment. But there is few studies on the calculation of the urban heat island intensity at present. In this paper, the brightness temperature of the case image in Hefei city is calculated based on the theory of Remote Sensing. The urban construction land is considered at the same time. The spatial distribution of the urban heat environment is analyzed and a calculation formula is obtained by using the fractal theory and the improved radius method. It is shown that there is a jump in the horizontal distribution of the brightness temperature between the urban built-up area and non-built up area. Then the intensity of the urban heat island is computed. The attention is focused on the spatial distribution features of the urban heat environment. This method avoids the confusion of having to find the temperature in the suburban, and it is an important point in the studies on the intensity of the urban heat island.