Identification of snail habitats in the Poyang Lake region, based on the application of indices on joint normalized difference vegetation and water / 中华流行病学杂志

ABSTRACT

Objective With Landsat TM remote sensing images,snail habitats in Poyang Lake region were identified,using two indicesthe 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.