| As a product of the advanced stage of industrialization and urbanization,urban agglomeration is not only a spatial carrier leading the regional development,but also a strategic development highland for China to participate in global competition.The Hangzhou bay agglomeration is located in the Yangtze river delta with a high level of urbanization.To a certain extent,the development trajectory of the urban agglomeration around Hangzhou Bay can reflect the future development direction of Chinese cities.By using the night light data,the stable light source in urban areas could be captured,and the degree of human social and economic activities can be intuitively reflected.Because of some advantages such as easy access,long time series and large space span,so these data are often not only used to monitor the process of urbanization but also explore the evolution patterns and laws of urban agglomerations.Based on the night lighting data of DMSP/OLS and NPP/VIIRS,firstly,the spatial scopes of built-up areas of Hangzhou Bay urban agglomeration(HBUA)from 2002 to 2017 were extracted,and then the changes of scale,structure and morphological characteristics of HBUA during its development were analyzed by selecting various indicators and models,such as total amount of light,mean value,standard deviation ellipse,aggregation degree and primacy degree.Finally,the development trajectory of each city was analyzed by selecting some indicators and models,such as the expansion speed,the center of gravity of urban lighting,urban expansion wind rosette,etc.The main research contents and conclusions are as follows:(1)A methods of extracting built-up areas from two kinds of night-light data were established according to urban agglomerations.Because between two kinds of data of DMSP/OLS data and NPP/VIIRS data,there are the differences in spatial-temporal resolution,spectral response and so on.On the one hand,in this paper,to realize the matching of two kinds of data in spatial resolution,these data were re-sampled to 1 km*1 km grid unit.On the other hand,DMSP was corrected and desaturated,also noise filtering was performed for data of NPP/VIIRS.Therefore,the difference between these two types of data in boundary extraction and total amount of night light could be reduced,thus,the night light data set composed of two kinds of data with a long time series were obtained.On this basis,the error between the built-up area of urban agglomeration and the statistical data is 8.8%.Although there are some differences between the extraction results from these two data,it can basically satisfy the needs of spatial-temporal dynamic analysis of urban agglomeration.(2)Analysis of the development trajectory of HBUA.From 2002 to 2017,the total area of HBUA increased from 558 km2 to 4411 km2,the cumulative increase is 6.9 times,indicating that the development of HBUA has been rapid in the past 16 years.HBUA develops in the northeast direction along the Qiantang River and undergoes the process of transformation from"Hangzhou Unipolar Growth" to "Hang-Yong Dual?core Driving".Besides,there are some differences in the level of development among these cities,in which,Hangzhou and Ningbo are the fastest growing cities,and they are the main driving forces for the development of HBUA.Shaoxing,Jiaxing and Huzhou also maintain a relatively high speed of development,while the development of Zhoushan is relatively slow due to its limitation of island topography.Based on the data of night light,above results on the development trajectory of HBUA have certain reference value for future development planning and policy making of Greater Bay Area. |
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