Abstract:

With rapid economic development ，urban sprawl becomes an important feature of urbanization in Chongqing However，population，environmental and social problems resulted from urban expansion has emerged In this paper we studied the characteristics and influencing factors of urban expansion in the metropolitan area of Chongqing Based on the multitemporal Landsat TM/ETM+ data of 1988，1995，2000，2002，2007 and 2009，we used normalized difference barren index （NDBI），renormalized difference vegetation index （RDVI） and improved normalized difference water index （revised NDWI），combined with threshold segmentation and mask processing to retrieve information of urban construction lands The combined use of the three indices has better performance than that of singleband or singleindex interpretation This method using automatic and semiautomatic extraction would be an effective way to identify urban construction lands with high accuracy Combined with socioeconomic data in the metropolitan area of Chongqing，we calculated an expansion speed index，an expansion intensity index，an expansion elastic index，a compactness index，an expansion index of urban construction land and an expanding direction analysis to study spatialtemporal dynamics of urban expansion The driving forces of urban expansion were analyzed by using Grey relational analysis The results showed that （1） the area of the urban construction lands expanded by 39332 km2 from 1988 to 2011，and the expansion presented an accelerated trend Especially during 2009-2011，the expansion area was 3667 km2，which accounted for 3812% of the total extension area during the whole study period （2） Fluctuations of expansion elastic index and expansion index of urban construction lands indicated a transformation from extensive to intensive expansion （3） Spatial characteristics of urban expansion showed that the urban areas in Chongqing developed from a noncompact to a compact form The extending direction showed obvious spatial differentiation，with  north and northwest as the main direction （4） Population growth，especially urban population growth is the main driving force of the expansion of urban construction lands Economic development and the transformation of the industrial structure also had a significant correlation with the expansion of urban construction land