Dynamic Supervision and Reason Analysis of Vegetation Coverage Changes of Chengdu in the Past 20 years

Using 1992,2001 and 2009 TM remote sensing data,the authors estimated the vegetation coverage change status of Chengdu in the past 20 years objectively and quantitatively.The study has practical significance for adjusting the climate,resuming the vegetation and preventing the natural disasters.Normalized difference value vegetation index(NDVI) was used to estimate the vegetation coverage in different periods and draw the change grayness and change levels chart of Chengdu vegetation coverage.Data analysis results show that,from 1992 to 2009,the vegetation coverage in Chengdu was overall decreasing.The quantity of dense forest land,shrub land,high and middle grass and cultivated land was decreasing,in which the vegetation coverage decreased obviously from 1992 to 2001,the vegetation coverage remained reduced from 2001 to 2009,but the speed was slower than that from 1992 to 2001.In addition,the speckle distribution of artificial greenbelt appeared in the urban area,and the small-area climatic condition was improved continuously.