联合应用归一化水体和植被指数提取鄱阳湖区钉螺孳生地的研究

Identification of snail habitats in the Poyang Lake region, based on the application of indices on joint normalized difference vegetation and water

目的应用LandsatTM遥感图像，联合应用归一化水体指数（MNDwI）和植被指数（NDVI）定量化确定鄱阳湖区的钉螺孳生地。方法利用鄱阳湖地区丰水期和枯水期TM卫星遥感图像，分别提取改进型MNDWI，获取“冬陆夏水”区域；同时提取枯水期归一化植被指数，获取有植被覆盖区域，将两者叠加确定钉螺孳生地，最后与现场调查资料进行空间叠加分析提取结果的灵敏度和特异度，并与传统经验提取法比较。结果在TM卫星遥感图像上，丰水期和枯水期的MNDWI阈值分别为0．34和0．58，枯水期NDVI的阈值为0．02。钉螺孳生地提取结果的灵敏度为95％，特异度为100％，远优于传统经验提取法（灵敏度为75％，特异度为100％）。结论联合应用MNDWI和NDVI，并以客观确定阈值提取钉螺孳生地的方法准确率高，可为血吸虫病的定量化自动监测提供技术支持。

Objective With Landsat TM remote sensing images, snail habitats in Poyang Lake region were identified, using two indices： the modified normalized difference water index （MNDWI） and the normalized difference vegetation index （NDVI）. Methods Two Remote sensing images of both wet and drought seasons in Poyang Lake region were obtained. MNDWI and NDVI were extracted from the images respectively, to present the regions of ＂water in summer and land in winter＂ and the coverage of vegetation. By overlaying those two regions, the areas of potential snail habitats were drawn. Finally, sensitivities and specificities of the recommended methods were assessed and compared to that of the traditional methods for the sake of extracting the areas of snail habitats. Results The threshold values of MNDWI for the wet and drought seasons were 0.34 and 0.58, respectively and the threshold value for NDVI of the drought season was 0.02. Sensitivity and specificity of our method were 95% and 100%, respectively, higher than the conventional approach （se.=75% , sp. = 100% ）. Conclusion Joint application of MNDWI and NDVI seemed a better method to detect the snail habitats and could be used for the quantitative and automatic surveillance program on snails.