Changes in Spatial Patterns of Urban Landscape in Bohai Rim from 1992 to 2010 Using DMSP-OLS Data

Abstract

The photoelectric amplification characteristics of Operational Linescan System(OLS) sensors on board of the Defense Meteorological Satellite Program's(DMSP) satellites make the instruments sensitive to low visible lights in the night which can distinguish the differences of light signals between urban and rural areas.Remotely sensed nighttime lights datasets derived from the DMSP-OLS sensors have been extensively applied to assess and monitor the process of urbanization and human activities,which has become an important data source for studies on regional urbanization and human activities.Methods used to extract urban built-up areas from DMSP-OLS data,such as empirical global thresholding-based methods and the sudden detection method,cannot avoid their own defects.The experience thresholding values are not universal in different regions and the sudden detection method cannot be applied in large scales.In this study,we corrected the experience thresholding values by introducing statistical data of some sample cities in the research area which combined with a calibration process to DMSP-OLS time serial data for extracting urban built-up area from satellite-based nighttime light data at large temporal and spatial scales.Nine landscape metrics: the number of patches(NP),the landscape total area(TA),the mean patch size(MPS),the largest patch index(LPI),the patches density of per hundred km2(PDh),the landscape shape index(LSI),the total edge length(TE),the edge density(ED) and the radius of gyration(GYRATE) are calculated by the FRAGSTATS3.3 software to analysis the spatial pattern change characteristics of urban area in Bohai Rim.The study showed that from 1992 to 2010,the urbanization in Bohai Rim experienced a continuing and rapid process.In this region,the total urban built-up areas expanded for 2.14 times,the average built-up area of cities increased for 76%,the gyrate of extracted urban patches expanded about 26.5% which suggested that the complexity of urban patch shapes were increased.The amount of detected urban patches got 82% increase but the number of isolate cities in each 100 km2 were decreased by about 76% which implied that the expansion of traditional cities was the dominant factor of the area increasing rather than continuously emerging towns.The expansions of metropolises were slower than small cities,and the overall landscape fragmentation degree was decreased gradually with the trend of urban area connection between core cities and their exurbs.