The continuous expansion of urban land has led to massive encroachment upon cropland. To examine the impacts of urban expansion on the loss and fragmentation of cropland in China’s nine major grain production areas (MGPAs), we used standard deviation ellipse, land use transfer matrix, land use dynamic degree, and landscape metric to explore the spatio-temporal evolutions, mutual transfer, and landscape patterns of cropland and urban land. The results show the following: (1) From 1995 to 2018, the areas of cropland in MGPAs showed a trend of “short-term increase—long-term decrease—short-term increase”, while that of urban land grew continuously; (2) Urban expansion is the main cause of cropland loss. The cropland area converted to urban land accounts for a large proportion (49.26%) of the total transfer of cropland to other land types, especially in the densely populated, rapidly urbanizing and industrializing Taihu Lake Plain, Jianghuai Region, and Pearl River Delta; (3) In most MGPAs, urban expansion has led to fragmentation of cropland, especially in the Pearl River Delta, as indicated by the significant change of patch density. However, in the Sanjiang Plain and Songnen Plain, a less pronounced or even reduced cropland fragmentation was observed due to the significant conversion of other land types to cropland under specific land policies. From these results, we suggest that the government should regulate the encroachment of urban land on cropland and the transfer of natural land to it, and encourage the rural land consolidation to increase the cropland.

研究黄河流域建成区扩展特征有助于透视用地开发效果和践行中心城市高质量发展规划。基于1992、1997、2002、2007、2012、2018年6期夜间灯光影像与统计数据，提取建成区范围，采用扩展强度指数、紧凑度指数、协调发展系数与灰色关联分析，探究1992—2018年黄河流域8个中心城市扩展的时空格局、质量及动力因子。结果表明：（1）黄河流域中心城市建成区面积分化明显，中下游城市扩展规模和强度大，扩展形态呈紧凑度普遍下降趋势。（2）夜间灯光影像数据刻画的西安建成区综合水平高、西宁水平低，银川综合发展快、兰州慢；除西宁、呼和浩特与太原外，其他中心城市平均夜间灯光指数在1997—2018年呈下降趋势，反映城市扩展水平降低。（3）中心城市人口-土地协调发展系数均呈波动下降趋势，除呼和浩特、太原和济南外，人口-土地由基本协调型向土地过快扩展型转变；中心城市经济-土地协调发展系数呈波动下降趋势，经济年均增长率降低，建成区面积年均扩展率增加，基本由经济过快增长型向经济-土地协调发展型转变。（4）中心城市空间扩展主要受经济发展（地区生产总值）影响；从中心城市整体看，全时段（1996—2018年）行政力（固定资产投资）和内源力（人口规模）影响作用较大，分时段（1996—2002年、2002—2012年与2012—2018年）行政力影响系数亦较高，市场力（社会消费品零售总额）与外向力（实际利用外资额）影响作用程度随时间增加明显。新时期黄河流域中心城市空间扩展应注重内部提质增效，提高建设用地利用效率，促进城市高质量发展。

Africa has been experiencing a rapid urbanization process, which may lead to an increase in unsustainable land use and urban poverty. Assessing the spatiotemporal characteristics of urbanization dynamics is especially important and needed for the sustainable development of Africa. Satellite-based nighttime light (NTL) data are widely used to monitor the dynamics of urban growth from global to local scales. In this study, urban growth patterns across Africa were analyzed and discussed using stable nighttime light datasets obtained from DMSP/OLS (the Defense Meteorological Satellite Program’s Operational Line-scan System) spanning from 1992 to 2013. We partitioned the nighttime lighting areas into three types (low, medium, and high) using thresholds derived from the Brightness Gradient (BG) method. Our results indicated that built-up areas in Africa have increased rapidly, particularly those areas with low nighttime lighting types. Countries with higher urbanization levels in Africa, like South Africa, Algeria, Egypt, Nigeria, and Libya, were leading the brightening trend. The distribution of nighttime lighting types was consistent with the characteristics of urban development, with high nighttime lighting types showed up at the urban center, whereas medium and low nighttime lighting types appeared in the urban-rural transition zone and rural areas respectively. The impacts of these findings on the future of African cities will be further proposed.

Urbanization has an abundant connotation in dimensions such as population, economy, land, and society and is an important sign to measure regional economic development and social progress. The use of Night Light Data from remote sensing satellites as a proxy variable can significantly improve the accuracy and comprehensiveness of the measurement of urbanization development dynamics. Based on the Night Light Data and statistical data from 2015 to 2019, this paper quantitatively analyzes the spatio-temporal evolution pattern of urbanization in Guangxi and its driving mechanism using exploratory time-space data analysis, GeoDetector and Matrix: Boston Consulting Group, providing an important basis for sustainable urban development planning and scientific decision-making by the government. The findings show that (1) there is a high level of spatial heterogeneity and spatial autocorrelation of urbanization in Guangxi, with the Gini index of urban night light index and urban night light expansion vitality index always greater than 0.5, the global Moran’s I greater than 0.17, the spatial differentiation converging but the spatial correlation increasing. (2) The spatial pattern of urbanization in Guangxi has long been solidified, but there is a differentiation in urban development trend, with the coexistence of urban expansion and shrinkage, requiring differentiated policy design for urban governance. (3) The development and evolution of urbanization in Guangxi present a complex intertwined dynamic mechanism of action, with interaction effects of bifactor enhancement and non-linear enhancement among factors. It should be noted that the influence of factors varies greatly, with the added value of the tertiary industry, gross domestic product, total retail sales of social consumer goods having the strongest direct effect on the urban night light index, while the added value of secondary industry, per capita GDP, gross domestic product having the strongest direct effect on the urban night light expansion vitality index. All of them are key factors, followed by some significant influence factors such as government revenue, population urbanization rate, per government revenue, population urbanization rate, per capita disposable income of urban and rural residents that should not be ignored, and the rest that play indirect roles mainly by interaction.

In recent years, much attention has been given to the current situation and trend regarding economic development in the Democratic People’s Republic of Korea (DPRK), of which urbanization is an important indicator. In the present study, (i) the urbanized area is estimated using DMSP/OLS and NPP/VIIRS, (ii) the current spatial pattern and the change characteristics of typical cities are revealed, and (iii) the scale and developmental stage of major cities in the DPRK are judged through comparison. Although the DPRK is relatively closed, the financial crisis in 2008 indirectly affected its economic development, and a large gap remains between the urbanization level of the DPRK and that of China and the Republic of Korea. The large cities in the DPRK are located mainly in its eastern coastal areas and western plains, and there has been no significant expansion in Pyongyang, Chungjin, and Hamhung in the past 28 years. Although economic construction has begun again recently in the DPRK, further reform and opening are required. As the DPRK’s relations with its neighbors and countries around the world improve, its economic development and urban construction will present a new pattern.

夜间灯光影像容易受到道路灯光、水面散射等影响而产生背景噪声,这一定程度上影响了利用夜间灯光数据提取建成区的精度。本文基于夜间灯光影像的DN（Digital Number）值与路网密度正相关、与EVI指数（Enhanced Vegetation Index,增强型植被指数）呈负相关的规律,提出了2种可用于建成区提取的夜间灯光亮度修正指数：EVI夜间灯光亮度修正指数EANI (EVI Adjusted Nighttime Light(NTL) Index)和基于道路网密度与EVI指数的夜间灯光亮度修正指数REANI (Road Density & EVI Adjusted NTL Index),并利用珞珈1号卫星（LJ1-01,分辨率约130 m）影像和NPP-VIIRS影像（分辨率约 500 m） 2种不同空间分辨率夜间灯光遥感影像进行验证。以2018年徐州市建成区为研究对象,分区域（主城区、外围区）利用阈值法对2种原始夜间灯光影像、经EANI指数和REANI指数处理后的影像进行建成区提取,得到6种建成区提取的结果。研究表明： ① EANI指数和REANI指数能够有效抑制夜间灯光影像的背景噪声,建成区提取的结果均优于直接利用原始影像的结果,特别是对于城市化水平较低地区的建成区提取效果更佳;② 相较于NPP-VIIRS影像,利用LJ1-01影像提取建成区的效果提高6%左右,说明我国的LJ1-01夜间灯光影像在建成区提取方面有广阔的应用前景。EANI和REANI为建成区提取提供了有效工具,并可应用于城市规划和城市扩张等研究领域。

在遥感应用研究中,夜间灯光遥感作为发展活跃的一个重要分支,近年来受到越来越多来自自然科学领域和社会经济领域的关注。与传统的光学遥感卫星获取地物辐射信息不同,夜间灯光遥感是获取夜间无云条件下地表发射的可见光-近红外电磁波信息。相比于普通的遥感卫星影像,夜间灯光遥感所使用的夜间灯光影像记录的地表灯光强度信息更直接反映人类活动差异,因而被广泛应用于城市化进程研究、不透水面提取、社会经济指标空间化估算、重大事件评估、生态环境评估等领域。目前,虽然基于夜间灯光数据的应用研究成果正在不断积累,但对成果的系统性总结、整理的研究目前存在着覆盖面不全、时效性不强等不足。基于此,论文通过对近几十年来有关夜间灯光数据的研究成果的详细梳理,从数据处理与技术方法、应用研究等方面进行归纳总结。最后,文章从多源数据融合、应用领域拓展和短周期地表灯光监测3个方面指出了未来的研究热点。

In remote sensing research, night light remote sensing as an important branch of active development has attracted increasingly more attention from the fields of natural and social science research in recent decades. Different from traditional daytime optical satellite remote sensing that obtains ground object radiation information, nighttime light remote sensing is the acquisition of visible-near-infrared electromagnetic information transmitted from the Earth's surface under cloud-free conditions at night. Compared to the ordinary satellite remote sensing images, ground light intensity information recorded by the night light images directly reflects the difference of human activity. Therefore, it is widely used in urbanization research, extraction of impervious surfaces, estimation of socioeconomic indicators, major events assessment, ecological environment assessment, and other fields. At present, although research results based on nighttime light data are continuously accumulating, there is a general lack of systematic review of these results and the current reviews suffer from incomplete coverage and poor timeliness. Therefore, this article summarizes the research results of nighttime light data in recent decades and examines them from the aspects of data processing and technical approaches, urbanization application research, and parameterization. Finally, we identify the following three research hotspots: multi-source data fusion, application expansion, and short-period surface light monitoring.

A consistently processed annual global nighttime lights time series (2012–2019) was produced using monthly cloud-free radiance averages made from low light imaging day/night band (DNB) data collected by the NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS). The processing steps are modified from the original methods developed to produce annual nighttime lights products from nightly data. Only two years of VIIRS nighttime lights (VNL) were produced with the V.1 methods: 2015 and 2016. Here we report on methods used to produce a V.2 VNL time series from the monthly averages with filtering to remove extraneous features such as biomass burning, aurora, and background. In this case, outlier removal is achieved with a twelve-month median, which discards high and low radiance outliers, thus isolating the background to a narrow range of radiances under 1 nW/cm2/sr. Background areas with no detectable lighting are further isolated using a statistical measure of texture, 3 × 3 data range (DR). The DR threshold for zeroing out background rises as the number of cloud-free observations falls. The V.2 method extends the temporal leverage in the noise filtering by developing the DR threshold from a multiyear maximum DR and a multiyear percent cloud-free grid. Additional noise filtering is achieved by zeroing out grid cells that have low average radiances (<0.6 nW/cm2/sr) and detection in only one or two years out of eight. The spatial extent and average radiance levels are compared for the V.1 and V.2 2015 VNL. For the vast majority of grid cells, the average radiances are nearly the same in the two products. However, the V.2 product has more areas of dim lighting detected. The key advantages of the V.2 time series include consistent processing and threshold levels across all years, thus optimizing the set for change detection analyses.

夜光遥感影像数据可有效反映城市空间格局变化。本文基于1992—2012年的DSMP-OLS夜光遥感影像和2018年的珞珈一号遥感影像,利用分层阈值法提取粤港澳大湾区内各城市建成区;通过计算平均灯光强度、平均灯光增长速率、城市建成区面积、城市建成区增长速率、城市重心、城市重心偏移距离等一系列指数,揭示区内各城市的空间格局演变过程。研究结果表明:①1992—2018年,粤港澳大湾区的城市规模大幅增长,沿珠江口两侧形成了以澳门、广州、深圳和香港为核心的倒“U”形城市群,并呈辐射状向周边扩张。②以珠江口为界,粤港澳大湾区东部各个城市的发展水平整体高于西部各个城市,广州、深圳、香港等核心城市发展水平明显高于江门、肇庆、惠州等外围城市。③1992—2018年,粤港澳大湾区建成区的增长速率由小变大,最后逐渐趋于稳定,2002—2007年是城市扩张最迅猛时期。④1992—2018年,粤港澳大湾区的各城市重心迁移方式表现为3种类型:持续向区域中心迁移;持续向相邻城市邻接区迁移;持续向海洋方向迁移。大部分城市的重心迁移方向呈“震荡”特征。

Nighttime light remote sensing images can be effectively used to extract evolution of urban spatial pattern. In this paper, the DSMP-OLS nighttime light (NTL) images from 1992 to 2012 and the LJ-1 NTL images in 2018 are used to extract urban built-up areas of Guangdong-Hong Kong-Macao greater bay area (GBA) by applying dynamic threshold method. On this basis, in order to reveal the spatial pattern and urban expansion process of each city in GBA, a number of indicators are used, including average light brightness, growth rate of average light brightness, urban built-up area, growth rate of urban built-up area, urban center of gravity coordinates, and offset distance of urban center of gravity. Finally, we analyze the main driving factors of urban expansion in GBA combined with the national economic statistics. The results show that:① From 1992 to 2018, the urban scale of GBA increased significantly. It forms an inverted "U" shaped urban agglomeration, with Guangzhou, Shenzhen and Hong Kong as the center, expanding outward in a radial manner. ② Taking the Pearl River Estuary as the boundary, the development level of eastern cities is significantly higher than that of western cities. The development level of core cities such as Guangzhou, Shenzhen and Hong Kong were significantly higher than that of peripheral cities such as Jiangmen, Zhaoqing and Huizhou. ③ From 1992 to 2018, the expansion speed of the built-up area in GBA increases from small to large, and then decreased gradually. 2002-2007 was the fastest period of urban expansion. ④ From 1992 to 2018, there were three types of urban center of gravity migration:the center of gravity of periphery cities continued to move to the center of GBA, the center of gravity of central cities moved to the junction of neighboring cities, the center of gravity of special administrative cities is moving towards the ocean. Most cities have "vibration" in their directions of urban gravity movement.

土地开发已成为当前研究的一个焦点，但是对“土地财政”现象的研究仍集中在其形成机制方面，而很少证实土地是否及如何推动了地方财政收入的增长。为此，本文基于《城市统计年鉴》（1985-2011） 的面板数据，构建面板误差修正模型和随机效应模型，运用格兰杰因果检验探讨城市建设用地扩张与城市财政收入增长之间的因果关系，并对“土地财政”的影响机制、区域差异和开发效率进行初步探讨。结果显示，从1995 年开始，中国城市的土地开发是推动其地方财政收入增长的格兰杰原因。但是这种效应主要为即期的影响，而对房地产开发和工业增值税的长期推动效果不太显著，这暗示了土地财政在中国有过度的倾向。从区域差异来看，土地开发对地方财政收入的推动幅度在中西部地区或在100 万人口以上的超大城市更大，且随城市规模的增加其影响效果更为显著。