基于长时间序列夜间灯光数据的京津冀城市群城市化过程

Urbanization in the Beijing-Tianjin-Hebei urban agglomeration in China based on long-term nighttime light data

近几十年来,随着全球城市化进程的加快,城市群成为一种区域主流空间形态。城市群的城市化时空格局是城市可持续发展与管理研究的重要内容。本文以京津冀城市群为例,基于2000—2018年长时序夜间灯光数据,计算并筛选适合于该地区的夜间灯光(NTL)强度指标和动态阈值,在NTL遥感影像基础上提取城市区域,综合利用景观指标和标准差椭圆参数研究城市群城市化演进过程。研究表明:(1)京津冀城市群的城市化进程发生了显著的阶段性变化,其进程可划分为3个阶段:第一阶段为2000—2010年核心城市快速城市化阶段;第二阶段为2010—2015年核心城市及其周边卫星城市的城市化波动发展阶段;第三阶段为2015年以后以中等城市为主的稳定城市化阶段。(2)京津冀城市群城市化的空间演化格局具有明显的的东北—西南方向性。(3)京津冀城市群的城市化以北京、天津两个核心城市为快速扩张区,辅之小城市的低速扩张,从而实现区域间的协同发展。本文证实了长时序NTL数据能有效且低成本地监测区域尺度上的城市化进程,可为城市化过程的动态时空格局研究提供方法借鉴。

In recent decades,as a result of the rapid urbanization globally,urban agglomerations have merged as an advanced spatial form of integrating cities.Investigating spatiotemporal patterns of urbanization in urban agglomerations is essential for urban sustainable development and management.In this study,remote sensing data,including extended time-series nighttime light(NTL)data and land-use images from 2000 to 2018,were used to examine the spatiotemporal patterns and evolution of urbanization over the last two decades in one of the most developed urban agglomerations in China:the Beijing-Tianjin-Hebei urban agglomeration.A multi-metric-based approach was synthetically used to facilitate the analysis.This study first calculated NTL intensity indices and dynamic NTL intensity thresholds.Then urban area was extracted from NTL images.Landscape metrics and the standard deviation ellipse were used to evaluate urban evolution in the study area.The results suggest that:(1)The urbanization process in the Beijing-Tianjin-Hebei urban agglomeration has undergone significant changes,and the process can be divided into three stages:rapid urbanization of the core cities from 2000 to 2010;fluctuating urbanization development of the core cities and their surrounding satellite cities from 2010 to 2015;and the stable urbanization stage with urbanization development mainly in medium-sized cities after 2015.(2)The spatial evolution of urbanization in the Beijing-Tianjin-Hebei urban agglomeration has an obvious northeast to southwest orientation.(3)The urbanization of the Beijing-Tianjin-Hebei urban agglomeration takes the two core cities of Beijing and Tianjin as the rapid expansion areas,complemented by the low-rate expansion of smaller cities,thus realizing a synergistic development of the region.This study confirmed that long time series NTL data can effectively and inexpensively monitor the urbanization process at the regional scale,and provides a methodological reference for the study of the dynamic spatial and temporal patterns of urbanization in the Beijing-Tianjin-Hebei urban agglomeration.