The fast urban expansion has led to replacement of natural vegetation-dominated land surfaces by various impervious materials. This has a significant impact on the environment due to modification of heat energy balance. Timely understanding of spatiotemporal information of impervious surface has become more urgent as conventional methods for estimating impervious surface are very limited. In response to this need, this paper proposes a new index, normalized difference impervious surface index (NDISI), for estimating impervious surface. The application of the index to the Landsat ETM image of Fuzhou City and the ASTER image of Xiamen City in China has shown that the new index can efficiently enhance and extract impervious surfaces from satellite imagery, and the normalized NDISI can represent the real percentage of impervious surface. The index was further used as an indicator to investigate the impact of impervious surface on urban heat environment by examination of its quantitative relationship with land surface temperature (LST), vegetation, and water using multivariate statistical analysis. The result reveals that impervious surface has a positive exponential relationship with LST rather than a simple linear one. This suggests that the areas with high percent impervious surface will accelerate LST rise and urban heat island development.

城市空间的快速扩展已使得原来以植被为主的自然景观逐渐被人工不透水建筑物所取代，并对区域乃至全球的生态系统造成了明显的影响。因此，准确了解城市不透水面及其与植被、水体、城市热环境的相关关系对于城市的科学规划和城市生态系统的修复具有重要的意义。以福州市为例，采用遥感空间信息技术，获得了城市不透水面、地表温度、植被和水体的信息，并对它们的关系进行了定量分析。发现了城市不透水面与地表温度之间的关系并不是一种简单的线性关系，而是一种很显著的指数函数关系，说明高不透水面比例地区的升温效应要明显高于低不透水面比例地区。多元统计分析表明不透水面是引发城市热岛的最重要因子。

Urban spatial expansion in the Quanzhou region of southeastern China has been accelerated over the past 20 years. This has caused land cover changes and, thus, has significant impacts on the local ecosystem and climate. To study the urban expansion and heat island dynamics of the region over the past 20 years, multitemporal Landsat TM images of 1987, 1996, and 2006 were used. The estimation of the urban expansion was assisted by the index-based built-up index (IBI) through enhancing built-up land features in the images. The urban-heat-island (UHI) effect was assessed using the urban-heat-island ratio index (URI). Multitemporal analysis indicates that the great increase in urban area has resulted in the development of UHIs in the region. Regression statistics reveal that built-up land has a positive exponential relationship with land surface temperature (LST). Therefore, the increase in built-up land percentage can exponentially accelerate the rise of LST.

Landsat TM images were employed to characterize land-cover types and land-cover changes in Fuqing City and its adjacent areas in Fujian Province, southeast China. Three TM scenes from 1991, 1994 and 1996 were used to cover the city and the adjacent areas and a ®ve-year time period. Socio-economic data were also integrated with remotely sensed data for the study. Digital image processing with assistance of GIS has produced three classi®ed image maps. The comparison of the three maps reveals that the urban expansion was very rapid, a large number of arable lands have been lost, and deforestation has taken place in the study area during the ®ve study years. The main driving forces to the urbanization appeared to be the rapid economic development and trac infrastructure. The suggestion on the regional sustainable development for the county is also presented.

The normalized difference water index (NDWI) of McFeeters (1996) was modified by substitution of a middle infrared band such as Landsat TM band 5 for the near infrared band used in the NDWI. The modified NDWI (MNDWI) can enhance open water features while efficiently suppressing and even removing built-up land noise as well as vegetation and soil noise. The enhanced water information using the NDWI is often mixed with built-up land noise and the area of extracted water is thus overestimated. Accordingly, the MNDWI is more suitable for enhancing and extracting water information for a water region with a background dominated by built-up land areas because of its advantage in reducing and even removing built-up land noise over the NDWI.