21世纪以来,太湖地区蓝藻的爆发严重影响了当地水资源的开发与利用。以太湖蓝藻为研究对象,以快速提取含蓝藻水体为目标,基于Landsat8影像对比分析了非蓝藻水体与含蓝藻水体光谱反射特征。含蓝藻水体在近红外波段表现出强反射率特征,而在蓝光、绿光、红光、短波红外波段的反射特征与非蓝藻水体一致,据此提出了一种提取含蓝藻水体信息的方法——双红外水体指数(double infrared band water index, DIBWI)。基于太湖地区2014年和2017年的Landsat8影像,与归一化差异水体指数(normalized difference water index, NDWI)、改进的归一化差异水体指数(modified normalized difference water index, MNDWI)、新型水体指数(new water index, NWI)、多波段水体指数(multi-band water index, MBWI)和水体指数2015(water index 2015, WI2015)这5种水体指数提取结果进行了对比分析,并利用2013年、2016年和2018年3期数据进行验证。结果表明,DIBWI能够较完整地提取含蓝藻水体信息,有效消除蓝藻影响并能抑制背景地物,总体精度达到98%以上,Kappa系数大于0.95,可以为太湖地区水资源保护、合理开发利用提供技术支撑。
Since the 21st century, the outbreak of cyanobacteria in the Taihu Lake has seriously affected the development and utilization of local water resources. Based on Landsat8 imagery, this paper analyzes the spectral reflection characteristics of non-cyanobacteria water and cyanobacteria water. Cyanobacteria water shows strong reflectance characteristics in the near-infrared band, but the reflectance characteristics in the blue, green, red and shortwave-infrared bands are the same as those in non-cyanobacteria water. On such a basis, a method for extracting cyanobacteria water information, i.e., double infrared band water index (DIBWI), is proposed. On the basis of the Landsat8 imageries of 2014 and 2017 in Taihu Lake area, the comparison and analysis were made with the results of normalized difference water index (NDWI), modified normalized difference water index (MNDWI), new water index (NWI), multi-band water index (MBWI) and water index 2015 (WI2015), and the data of 2013, 2016 and 2018 were used for verification. The results show that DIBWI can extract the cyanobacteria water information, effectively eliminate the influence of cyanobacteria and better inhibit the background features. The overall accuracy is above 98%, and the Kappa coefficient is more than 0.95, which can provide technical support for the protection and reasonable development and utilization of water resources in Taihu Lake area.
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