从DMSP-OLS数据提取城市区域的经验阈值法存在固有的缺陷, 经验阈值对不同的空间区域不具备通用性, 不适用的经验阈值, 将导致城区面积提取具有较大误差, 可采用统计数据对经验阈值进行修正以降低误差。本文在大时空尺度条件下以少量样本城市的统计数据对经验阈值方法进行了修正;另采用Elvidge二次多项式模型对DMSP-OLS时间序列数据进行了校正。在此基础上选取总斑块数量、景观总面积、平均斑块大小、最大斑块面积比、斑块密度、景观形状指数、总边界长度、平均边界密度和斑块平均回旋半径共9个景观生态学指标, 采用FRAGSTATS 3.3软件计算分析了1992-2010年环渤海区域城市发展的空间格局变化特征。结果表明:1992-2010年间, 环渤海区域城市化进程持续较快发展, 城市建成区总面积增加了2.14倍, 平均城市建成区面积增加了76%, 提取到的城市斑块平均回旋半径增加了约26.5%, 并且城市景观斑块的复杂度明显上升, 可检测到的城镇总个数增加了82%。但是, 每100km2内孤立的城市景观斑块数却降低了约76%;大城市持续扩张的相对速度慢于中小城市, 城市区域边界密度和整体城市分布景观格局破碎度逐渐降低, 核心城市与周围卫星城市的景观斑块的联通性逐步增加。
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.
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