[The use of unsupervised classification of Landsat-5 TM images in analysing the types of vegetation in the areas of "breaking dikes or opening sluice for water store"].

Objective: To clarify the change of vegetation types and its relationship between the density of alive-snails in the areas of "breaking dikes or opening sluice for water store" in Jicheng.

Methods: Synthesized false color images of Jicheng before and after 1998 (1994 and 2003) were classified without supervision and results were compared. Vegetation types were identified on the spot.

Results: Normalized difference vegetation index (NDVI) of snail habitats before 1998 were between 126 and 183 in Jicheng, whose vegetation types were mainly paddy, cotton and cabbage. NDVI of snail habitats in Jicheng after 1998 were between 152 and 193 whose vegetation types were mainly poplar forest, bulrush and grass. Areas of snail habitats increased from 64.64% to 66.47%. Snail habitats were mostly composed of mixed vegetation types and mono-typed vegetation was hardly found. According to the density of alive-snails orders from high to low were poplar forest and bulrush, poplar forest and grass, bulrush.

Conclusion: Vegetation types would not be identified by unsupervised classification only. Poplar forest, bulrush and grass were closedly related to the density of alive-snails.