Study on the relationship between Terra-MODIS image and the snail distribution in marshland of Jiangning county, Jiangsu province / 中华流行病学杂志

<p><b>OBJECTIVE</b>To analyze the relationship between the normalized difference vegetation index (NDVI) and the snail distribution in marshland of Jiangning county in Jiangsu province, and to explore the utility of Terra-MODIS image map in the small scale snail habitats surveillance.</p><p><b>METHODS</b>NDVI were extracted from MODIS image by vector chart of the snail distribution using ArcView 8.1 and ERDAS 8.5 software. The relationship between NDVI and the snail distribution were Investigated using Bivariate correlations and stepwise linear regression.</p><p><b>RESULTS</b>The snail density on marshland was positively correlated with the mean NDVI in the first ten-day of May and the maximum NDVI (N(20max)) in the last ten-day of May. Incidence of pixel with the live snail on marshland was positively correlated with the mean NDVI (N(2mean)) in the first ten-day of May. An equation Y(1) = 0.009 47 x N(20max) (R(2) = 0.73), Y(2) = 0.018 6 x N(2mean) (R(2) = 0.906) was established.</p><p><b>CONCLUSION</b>This study showed that the Terra-MODIS satellite images reflecting the status of the vegetation on marshland in Jiangning county could be applied to the study to supervise the snail habitat. The results suggested that MODIS images could be used to survey the small scale snail habitats on marshland.</p>

Application of satellite image for surveillance of vegetation landscapes of Oncomelenia-snail habitats in marshland using unsupervised classification / 中华流行病学杂志

<p><b>OBJECTIVE</b>To explore the vegetation landscapes in marshland snail habitats using satellite image.</p><p><b>METHODS</b>The false-color composition image from band 2, 3 and 4 of LANDSAT ETM + images was classified in the ERDAS IMAGINE 8.5 to analyze the vegetation types in the marshland of Jiangning county, using the unsupervised classification. The efficiency of classification was evaluated by the transformed divergence. The overlaid layers of the classified vegetation image and the vector layer of snail habitats distribution were used to analyze the relationship between the snail distribution and the landscape types.</p><p><b>RESULTS</b>The land-cover of marshland in LANDSAT ETM234 image in Jiangning county could be classified into 10 types, including water, bare soil, sandy and other landscapes while the transformed divergence analysis showed that there were misclassified pixes between some types especially for the non-continuous types. The study indicated that through adding the NDVI image in the process of classification efficiency of classification and eliminate misclassification in the non-continuous type could be improved. Analysis on the overlaid layer of the vector of snail distribution and the classified image proved that the vegetation covers in marshland snail habitats in Jiangning mainly belonged to type 3, 5 and 6, that responded to the beach with sparse vegetation, exuberant weed and bulrush respectively. The density of snails in the bulrush was higher than that in other 2 landscapes.</p><p><b>CONCLUSION</b>The vegetation type in the marshland snail habitats could be distinguished from the satellite image, which was helpful for the surveillance of snail habitat in marshland and for the prevention of schistosomiasis.</p>