Landsat ETM image of Lake Taihu acquired on Aug. 20, 2010 showed that there was black color water bloom (BCWB) near the shore of western part of the lake, the remotely sensed image was atmospherically corrected, several ROIs (Region Of Interest) were placed on BCWB area and other water bodies, the spectral reflectance statistics were extracted for these ROIs. Results showed that BCWB ROIs had very low reflectance at ETM visible bands 1 ,2 and 3 , hence had very dark to black water color, but at ETM reflective infrared band 4, they showed slightly high reflectance than band 3, hence the Difference Vegetation Index (DVI) had positive value. The cause was that despite the rapid degeneration of cyano-bacteria in BCWB, there still remain some live cyano-bacteria cells in the water bloom, the remnant chlorophylls and cell structure were able to reflect solar radiation at reflective infrared wavelengths. The criteria for identifying BCWB was proposed as p0. 485 < 0. 05 and po.56 <0.08 and p0.66 <0.065 and (p0. 83 -p066) >0 and p0. 83 <0. 1 .%2010年8月20日太湖地区Landsat ETM影像显示,太湖西部沿岸带存在湖泛黑水团现象,对该景遥感影像进行了大气校正,提取了湖泛样区、其他水体样区的ETM各波段光谱反射率数据统计特征.结果表明,湖泛样区在可见光波长的ETM波段1、2、3具有很低的反射率,水色暗黑,与人眼观察一致,而在反射红外波长的ETM波段4则有比波段3高的反射率,差异植被指数DVI＞0,其原因为湖泛黑水团中,虽然大量蓝藻死亡分解,然而水中还残留有一定数量的活体蓝藻,残余叶绿素及细胞造成了虽然较弱、但仍较为稳定的反射红外波长处的光谱反射能力.提出了识别湖泛现象的遥感判据为ρ0.485 ＜0.05 and ρ0.56＜0.08 andρ0.66＜0.065 and (ρ0.83-ρ0.66) ＞0 andρ0.83＜0.1.
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