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.

卫星遥感影像在接收的过程中由于受到许多因素的干扰, 使影像的质量受到一定程度的影响。而不同时相 的影像也会因为成像时光照和大气条件的不同而出现差异。因此, 在使用遥感影像之前往往需要进行必要的辐射校正。目前, 主要用于辐射校正的两种基于影像的正规化模型分别是Markham和Irish等人提出的校正日照差异的正规化模型(ICM) 和美国尤他州立大学遥感和地理信息系统实验室新近提出的日照大气综合校正模型(IACM/IACMt) 。本文以三对不同时相的Landsat TM/ETM +影像为例, 利用不变特征地物法求出各影像的相对噪音、RMSE和斜率, 并用这些指标来对模型进行定量对比和评价。结果表明, 当不同时相影像之间的季相、太阳天顶角和大气条件有较大差别时, 经过正规化处理的遥感影像的噪音和RMSE比未经正规化处理的影像得以明显降低,且斜率更接近于1, 镶嵌接缝淡化, 效果更好。但如果遥感影像之间的季相一致、成像时的太阳天顶角接近, 且影像晴空无云的话, 则经过正规化处理的影像和未经该处理的影像之间的区别并不大。就正规化模型之间的对比而言, 当影像无明显的大气影响时, ICM要好于IACM; 但当受到明显的大气影响时, 带有τ值的IACMt模型更好。

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.