Dynamics of Urban Expansion in Xi'an City Using Landsat TM/ETM+ Data
Received date: 2004-07-05
Revised date: 2004-11-09
Online published: 2005-01-25
Supported by
Sustainable Agroecosystem Management and Development of Rural-Urban Interaction in Regions and Cities of China (SUSDEV-CHINA), No.ICA4-CT-2002-10004; Knowledge Innovation Project of Chinese Academy of Sciences, No.KZCX3-SW-146
In this study, we extracted urban boundary of Xi'an with supervised classification and Normalized Difference Barren Index (NDBI), respectively. Supervised classification is the most common method in obtaining land use/cover information. In this study, after data pre-processing, training samples were selected according to spectral features. Unlike conventional classification of land use/cover, in this paper, only two classifications of land cover were chosen, which were urban areas and non-urban areas. This could avoid the urban areas from the effects of too many classes, so that the urban areas could avoid being divided into too many classes. Then maximum likelihood classification was used to map the land use/cover of Xi'an. NDBI is an index like NDVI (Normalized Difference Vegetation Index), which can reflect the information of barrens on the ground. As the spectrum of built-up area is similar to barrens, NDBI is used to obtain urban built-up information. Like NDVI, it is defined as NDBI = (band5-band4)/(band5+band4). By comparing the two different methods, we find that the urban boundary derived from TM image using supervised classification is more accurate than that using NDBI, because the image of NDBI contains not only urban information but also barrens. What's more, it is difficult to distinguish them. Thus, we achieved urban expansion of Xi'an from 2000 to 2003 using supervised classification. Through the analysis of urban boundary of Xi'an in 2000 and 2003, it shown that during the three years, urban expansion in Xi'an was very quick. The urban area of Xi'an in 2000 was 253.37 km2, but in 2003 it reached 358.60 km2, an annual average increase rate of 12.3%. By analyzing related statistics of Xi'an, we drew the conclusion that the rapid urban expansion in Xi'an has been closely related to the fast growth of social capital assets investment and economic development of the Xi'an city since great development of western China. The statistic data show that during the three years from 2000 to 2003, the social capital assets investment rose from 23.2 billion RMB to 47.9 billion RMB, and the GDP of the city of Xi'an grew to 94.0 billion RMB from 64.3 billion RMB. In addition, the increase of population and the development of infrastructure like traffics are also important factors to it.
Key words： urban expansion; supervised classification; NDBI; driving force; Xi’an
WU Hong'an, JIANG Jianjun, ZHOU Jie, ZHANG Hailong, ZHANG Li, AI Li . Dynamics of Urban Expansion in Xi'an City Using Landsat TM/ETM+ Data[J]. Acta Geographica Sinica, 2005 , 60(1) : 143 -150 . DOI: 10.11821/xb200501016
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