通过对归一化差异水体指数NDWI中的绿波段修正，提出了不依赖于中红外波段的伪归一化差异水体指数FNDWI（False NDWI）。使用NDWI和FNDWI分别在背景地物为城市、城郊、乡镇、村落和山区的遥感影像上进行河流水体提取，实验表明，FNDWI影像中城镇建筑用地与河流水体的可分离性较NDWI有所提升，提升率为116%~335%不等；相关性分析表明，河流宽度与可分离性提升率具有明显的负相关关系，相关系数为-0.82；分类结果显示，在城市和城郊区域，NDWI提取的水体中混杂有较多城镇建筑用地信息，而FNDWI提取的水体中基本未见混杂。总体上，FNDWI提高了2种地物的可分离性，剔除了NDWI影像混入的城镇建筑用地信息，较好地解决了NDWI城镇建筑用地与河流水体的混淆问题，尤其适用于城镇周边的细小河流。

The normalized difference water index (NDWI), (Green -NIR)/(Green+NIR), proposed by Mcfeeter, is widely used but easily to mix built-up land and water body due to the spectrum similarity on these two bands (green and near infrared reflection) between the two features (water body and built-up land). It is proposed by water indexes such as MNDWI, CIWI and NWI that importing mid-infrared (MIR) band could help solve the problem, as built-up lands have a higher value on MIR compared with NIR. However, more than half of the satellites have not a MIR band, such as Beijing-1 satellite, HJ-1A/B satellites, QuickBird, IKONOS, SPOT1-3 satellites and so on. A false normalized difference water index (FNDWI) has been proposed to fix the problem without access to MIR band. FNDWI replaces the green band in NDWI with a new FGreen (false green) band, which is created by adjusting the original green band with NIR band value. FNDWI has been tested with NDWI on five different typical regions, including urban, suburb, town, village, and non-built-up lands. The experiments reveal that FNDWI has depressed the value of built-up land, highlighted river water body, thus enhanced the differences between water and built-up land by 116% to 335% of NDWI, as well as remained the original NDWI difference between vegetation and water body. Also, it is found that there exits correlation between river width (measured by pixels) and difference enhancement from NDWI to FNDWI. Difference enhancement of thinner river areas is larger than that of wider river areas. Correlation coefficient between river width and difference enhancement reaches -0.82, indicating their apparent negative correlation. In urban, suburb and town regions, water extracting results using NDWI results are polluted by built-up land information while that using FNDWI is fairly clean. Above all, it is concluded that FNDWI is better than NDWI while extracting water bodies around built-up lands, especially on those thin rivers around urban areas.