AN ANALYSIS OF URBAN EXPANSION AND ITS DYNAMICS BASED ON MULTI-TEMPORAL LANDSAT DATA

Based on multi-temporal Landsat imageries,the authors extracted the urban built-up areas in Changsha City,Hunan province on the basis of such methods as supervised classification,unsupervised classification and NDBI index.The spatio-temporal patterns of the urban expansion were analyzed quantitatively by using the entropy value and differential entropy value of sequential urban land use images.Overlay and buffer spatial analysis were used to establish the relationship between the urban expansion and the distance from the city center.On such a basis,the expansion rate map was drawn to show the dominant direction of urban expansion.The results show that the urban built-up areas have continued to increase, and the expansion was directed mostly southeastward from 1973 to 1986,westward from 1987 to 1993,and southward and southeastward from 1994 to 2001.The rapid increase of population is thought to be the most important driving force of urban expansion.