A study of urban expansion of prefectural-level cities in South China using night-time light images

Because of its rapid economic development, China has been undergoing a dramatic urbanization process in recent decades. Such a process can be reflected by urban expansion, which can be represented by the change in urban built-up areas. In the literature, very little has been discussed on the extraction of built-up areas with a high frequency of acquisition for a large region. This article introduces a methodology to extract built-up areas using night-time stable light data. An improved calibration method is formulated to first eliminate the discrepancies across different satellites and years. A thresholding technique utilizing the sudden jump method is then employed to extract built-up areas for each prefectural city in each year. This method selects the best threshold by scrutinizing the sudden jump in the natural logarithms of the areas under different digital number (DN) thresholds. Moreover, the urbanization process of South China is examined using the extracted time series of built-up areas. The results show that such extracted time series represent changes in urban areas rather well when compared with the Thematic Mapper (TM) images, and a significant linear relationship between the extracted built-up areas and those of the land-use map and the China City Statistical Yearbook (CCSY) has also been established. Moreover, the empirical analyses also reveal that urban expansion took place in all cities from 1992 to 2010, especially in coastal cities, capital cities, and cities in the special economic zones.