Spatial Pattern Changes Of Yangtze River Delta Urban Agglomeration Using DMSP/NPP And Landsat Remote Sensing Data From 1992 To 2018

Cities are highly dense integrations of population,resources.environment and socio-economic factors.The central agglomeration of cities expands its scope to all sides.Urbanization is a process of increasing urban space,expanding urban scale and rural population centralization due to the development of social productive forces.Urbanization is the route that modernization must take.However,with the continuous expansion of cities,problems such as unbalanced regional development,inharmonious population,resources and environment have arisen.The urbanization level of urban agglomeration in the Yangtze River Delta is relatively high and its strategic significance is prominent,but there are outstanding contradictions such as development quality of urban agglomeration is rough,urban construction spreads disorderly,and the utilization rate of space is inefficient.It is of great significance to study the spatial pattern changes of urban agglomerations in the Yangtze River Delta for finding the regular pattern of urban expansion,evaluating urbanlization level,improving land utilization effiency and promoting the healthy and sustainable development of cities.In order to reveal the urban expansion pattern of the Yangtze River Delta urban agglomeration and explore the spatial and temporal pattern changes of the Yangtze River Delta urban agglomeration.In this paper,urban agglomeration in the Yangtze River Delta in 1992,1 995,2000,2005,2010,2015 and 2018 are taken as research objects.The urban districts of 121 cities above county level are extracted from Landsat images and nighttime light images.The results are compared with others urban area based on high and medium resolution.The characteristics of urban agglomeration are analyzed from the aspects of expansion area,expansion speed and expansion intensity.Finally,the standard of urban agglomeration is presented.The spatial pattern changes of urban system in the Yangtze River Delta urban agglomeration are analyzed from the aspects of standard deviation ellipse,rank-size distribution and spatial connection measure.The main conclusions of this paper are as follows:(1)The combination of Landsat and nighttime light data can effectively improve the accuracy and efficiency of urban area extraction.Compared with the only nighttime light data,the accuracy of extraction results can be improved.The extraction speed of urban area boundary can be effectively improved by taking the boundary automatically extracted based on Google Earth Engine cloud platform as the initial boundary and modifying it manually.Compared with the urban boundary results based on high resolution,the regression determinant coefficient of one-dimensional linear fitting is over than 0.97.(2)On the basis of extracting urban areas,the urban area change of the Yangtze River Delta urban agglomeration was analyzed.From 1992 to 2018,the urban area of the Yangtze River Delta urban agglomeration increased from 1773.56 km2 to 11757.63 km2,and the urban area in 2018 was 6.63 times as much as that in 1992.The urban area above prefecture level accounts for more than 70%of the urban area of the Yangtze River Delta urban agglomeration;although the urban area and expansion speed of county-level cities are far less than that of prefecture-level cities,the expansion intensity is 5.2 percentage points higher than that of prefecture-level cities;the urban area expansion speed varies from time to time,showing the characteristics of reducing first,then increasing to the maximum and then decreasing,and the urban expansion speed is the fastest in 2000-2005(3)Through analyzing the spatial pattern of urban agglomeration in the Yangtze River Delta by nightitme light images,the nighttime light spatial pattern of urban agglomeration in the Yangtze River Delta presents the characteristics of southeast-northwest direction,and the focus of nighttime light is always located in Taihu Lake;the urban scale of urban agglomeration in the Yangtze River Delta tends to be dispersed,the development of small and medium-sized cities continues to grow,and the urban system tends to be balanced,but it is still first-place distribution.The City gravitation of urban agglomeration is constantly increasing,and the regional development is obviously unbalanced.The Yangtze River estuary and the Taihu Lake Rim are the areas with large spatial connection.From the point of view of location,Shanghai has always maintained a high degree of location,and the cities with high degree of location are mostly located in Jiangsu,followed by Zhejiang and Anhui.However,in the north,west and south of the Yangtze River Delta urban agglomeration,the connection with the core cities is weak and the location is low.