A modified normalized difference water index（MNDWI） has been proposed in this paper based on the normalized difference water index（NDWI） of Mcfeeters （1966）

which uses MIR（TM5） instead of NIR（TM4） to construct the MNDWI. The MNDWI has been tested in the ocean

lake and river areas with the background of built-up lands and/or vegetated lands

and with both clean and polluted water bodies using Landsat TM/ETM+ imagery. This reveals that the MNDWI can significantly enhance the water information

especially in the area mainly with built-up land as background. The MNDWI can depress the built-up land information effectively while highlighting water information

and accurately extract the water body information from the study areas. While the enhanced water information using the NDWI always has been mixed with built-up land noise and the area of a water body extracted based on the index is thus overestimated. Therefore

the NDWI is not suitable for enhancing and extracting water information in built-up land-dominated areas. Furthermore

the MNDWI can reveal subtle features of water more efficiently than the NDWI or other visible spectral bands do due largely to its wider dynamic data range. The application of the MNDWI in the Xiamen image has achieved an excellent result. The MNDWI image successfully reveals significant non-point pollution of the water surrounding the Xiamen Island due to agricultural activities. In addition

taking the advantage of the ratio computation

the MNDWI can remove shadow noise from water information without using sophisticated procedures

which is otherwise difficult to be removed.