| 从增强型水体指数分析遥感水体指数的创建 |
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| 引用本文： | 徐涵秋.从增强型水体指数分析遥感水体指数的创建[J].地球信息科学,2008,10(6):776-780. |
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| 作者姓名： | 徐涵秋 |
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| 作者单位： | 福州大学环境与资源学院, 福州 350108 |
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| 基金项目： | 福建省重大专项前期研究项目
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| 摘 要： | 本文对新近提出的增强型水体指数(EWI)进行了分析和讨论,分别用经过大气校正和未经大气校正的两种影像来对该指数作了验证,并与改进的归一化差值水体指数(MNDWI)进行比较。结果表明该指数在经过大气校正的影像中对水体的增强和提取效果不理想,许多水体影像特征不但未能得到增强,反而受到抑制而被漏提。显然,该指数在创建时忽略了大气因素的影响。另外,该指数在构建上重复选择近红外和中红外波段也是造成提取效果不理想的原因之一。因此,为了创建正确的水体指数,避免水体增强和提取结果的偶然性和不确定性,水体指数的创建必须用经过大气校正的影像进行验证,而构建指数的波段也要避免不合理的重复选择,这样才能使所创建的指数具有更广的适应性。
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| 关 键 词： | 水体指数 大气校正 遥感 |
| 收稿时间： | 2008-06-11 |
Comment on the Enhanced Water Index (EWI) : A Discussion on the Creation of a Water Index |
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| XU Hanqiu.Comment on the Enhanced Water Index (EWI) : A Discussion on the Creation of a Water Index[J].Geo-information Science,2008,10(6):776-780. |
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| Authors: | XU Hanqiu |
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| Institution: | College of Environment and Resources, Fuzhou University, Fuzhou 350108, China |
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| Abstract: | This paper analyzes a newly proposed remote sensing index-the Enhanced Water Index(EWI),by Yan et al.(2007) and discusses the creation of a water index.The EWI was constructed by the ratio of the green light band to the sum of the near infrared(NIR) band and midddle infrared(MIR) band,i.e.,EWI=(Green-(NIR+MIR))/(Green+(NIR+MIR)).The evaluation of the EWI was through the application of the index in two images,one without atmospheric correction and the other with the atmospheric correction,and then the comparison of the results of the two enhanced images.Furthermore,the EWI-enhanced water images were also compared with the MNDWI-enhanced water images.The evaluation shows that the EWI failed to effectively enhance and extract the water features in the atmospheric-corrected image,while the MNDWI can work effetely in either corrected or uncorrected images.Many small open water bodies,such as ponds,lakes and city inner rivers,were omitted in the EWI-enhanced/extracted image.Obviously,the neglect of the atmospheric effect on the image resulted in the failure.In addition,the construction of the index is not reasonable.The increase in the concentrations of the suspended solids and algal chlorophyll can notably raise the reflectance of the NIR and MIR bands by water.Therefore,the difference in the reflectance between the green bands and the sum of the NIR and MIR bands can be significantly reduced and the EWI values of many such water bodies can be close to zero or even can be negative.Consequently,instead of being enhanced,these water features were depressed and even removed from the EWI-enhanced image,and thus resulted in the omission of the water features in the extracted EWI-water images.Therefore,in order to avoid uncertainty,any new water index to be created should be tested using atmospherically-corrected image beforehand.Moreover,the water components have also to be taken into account when constructing a water index. |
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| Keywords: | water index atmospheric correction remote sensing |
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