Investigating urban expansion patterns aids in the management of urbanization and in ameliorating the socioeconomic and environmental issues associated with economic transformation and sustainable development.Applying...Investigating urban expansion patterns aids in the management of urbanization and in ameliorating the socioeconomic and environmental issues associated with economic transformation and sustainable development.Applying Harmonized Defense Meteorological Satellite Program-Operational Line-scan System(DMSP-OLS)and the Suomi National Polar-Orbiting Partnership-Visible Infrared Imagery Radiometer Suite(NPP-VIIRS)Nighttime Light(NTL)data,this paper investigated the characteristics of urban landscape in West Africa.Using the harmonized NTL data,spatial comparison and empirical threshold methods were employed to detect urban changes from 1993 to 2018.We examined the rate of urban change and calculated the direction of the urban expansion of West Africa using the center-of-gravity method for urban areas.In addition,we used the landscape expansion index method to assess the processes and stages of urban growth in West Africa.The accuracy of urban area extraction based on NTL data were R^(2)=0.8314 in 2000,R^(2)=0.8809 in 2006,R^(2)=0.9051 in 2012 for the DMSP-OLS and the simulated NPP-VIIRS was R^(2)=0.8426 in 2018,by using Google Earth images as validation.The results indicated that there was a high rate and acceleration of urban landscapes in West Africa,with rates of 0.0160,0.0173,0.0189,and 0.0686,and accelerations of 0.31,0.42,0.54,and 0.90 for the periods of 1998–2003,2003–2008,2008–2013,and 2013–2018,respectively.The expansion direction of urban agglomeration in West Africa during 1993–2018 was mainly from the coast to inland.However,cities located in the Sahel Region of Africa and in the middle zone expanded from north to south.Finally,the results showed that the urban landscape of West Africa was mainly in a scattered and disordered’diffusion’process,whereas only a few cities located in coastal areas experiencing the process of’coalescence’according to urban growth phase theory.This study provides urban planners with relevant insights for the urban expansion characteristics of West Africa.展开更多
Human activities modulate the impact of environmental forcing in general and of climate in particular.Information on the spatial and temporal patterns of human activities is in high demand,but scarce in sparsely popul...Human activities modulate the impact of environmental forcing in general and of climate in particular.Information on the spatial and temporal patterns of human activities is in high demand,but scarce in sparsely populated and data-poor regions such as Northern Africa.The intensity and spatial distribution of nighttime lights provide useful information on human activities and can be observed by space-borne imaging radiometers.Our study helps to bridge the gap between the DMSP-OLS data available until 2013 and the NPP-VIIRS data available since 2013.The approach to calibrate the OLS data includes three steps:a)inter-calibrate the OLS DN data acquired by different sensors in 1992-2013;b)cali-brate the OLS DN data using VIIRS data in 2013;c)generate syn-thetic OLS radiance data by degrading the VIIRS data in 2013-2020.We generated a)a time series of calibrated OLS nighttime light radiance data(1992-2013);b)mean annual VIIRS radiance on stable lights at the OLS spatial resolution for 2013-2020;c)synthetic OLS radiance data generated using VIIRS radiance data degraded to match the radiometric specifications of OLS for 2013-2020.The evaluation of these data products in 2013 documented their accu-racy and consistency.展开更多
在全球变暖和人类活动的背景下,降水在年内分布上发生了比较大的变化,对人民生产生活产生了巨大的影响,这一影响在城市化较高的地区尤为明显。基于多源降水数据(降水产品数据和气象站点数据)和夜间灯光数据,选定中国的长三角城市群作为...在全球变暖和人类活动的背景下,降水在年内分布上发生了比较大的变化,对人民生产生活产生了巨大的影响,这一影响在城市化较高的地区尤为明显。基于多源降水数据(降水产品数据和气象站点数据)和夜间灯光数据,选定中国的长三角城市群作为研究区域,将基尼系数(Gini Index,GI)作为降水集中度的指标,利用Theil-Sen Median斜率估计和Mann-Kendall显著性检验进行趋势分析,最后通过相关性分析探究城市化程度与降水集中度的关系。研究结果表明:(1)CHIRPS(Climate Hazards Group InfraRed Precipitation with Station Data)数据计算得到的GI与站点数据结果的均方根误差为0.036,远小于CMFD数据(0.067)和MSWEP数据(0.083)的结果,表明CHIRPS数据具有最佳的适用性;(2)长三角城市群的降水不均匀性从南向北逐渐增加,并在城市群中部和西部呈现出显著上升的趋势,研究区域内的降水年内分布将会朝着集中分布的方向发展,极端降水事件出现的可能性增加;(3)城市化对降水集中度主要起到促进作用,城市的快速发展使得降水不均匀性增强,并且在城市群内的南京市、无锡市和镇江市等地区更为显著,更有可能发生城市内涝等灾害。研究对于城市的防洪设计、城市道路排水管道的设计和城市防洪应急响应预案的编制具有参考意义。展开更多
基金Under the auspices of National Natural Science Foundation of China(No.41971202)。
文摘Investigating urban expansion patterns aids in the management of urbanization and in ameliorating the socioeconomic and environmental issues associated with economic transformation and sustainable development.Applying Harmonized Defense Meteorological Satellite Program-Operational Line-scan System(DMSP-OLS)and the Suomi National Polar-Orbiting Partnership-Visible Infrared Imagery Radiometer Suite(NPP-VIIRS)Nighttime Light(NTL)data,this paper investigated the characteristics of urban landscape in West Africa.Using the harmonized NTL data,spatial comparison and empirical threshold methods were employed to detect urban changes from 1993 to 2018.We examined the rate of urban change and calculated the direction of the urban expansion of West Africa using the center-of-gravity method for urban areas.In addition,we used the landscape expansion index method to assess the processes and stages of urban growth in West Africa.The accuracy of urban area extraction based on NTL data were R^(2)=0.8314 in 2000,R^(2)=0.8809 in 2006,R^(2)=0.9051 in 2012 for the DMSP-OLS and the simulated NPP-VIIRS was R^(2)=0.8426 in 2018,by using Google Earth images as validation.The results indicated that there was a high rate and acceleration of urban landscapes in West Africa,with rates of 0.0160,0.0173,0.0189,and 0.0686,and accelerations of 0.31,0.42,0.54,and 0.90 for the periods of 1998–2003,2003–2008,2008–2013,and 2013–2018,respectively.The expansion direction of urban agglomeration in West Africa during 1993–2018 was mainly from the coast to inland.However,cities located in the Sahel Region of Africa and in the middle zone expanded from north to south.Finally,the results showed that the urban landscape of West Africa was mainly in a scattered and disordered’diffusion’process,whereas only a few cities located in coastal areas experiencing the process of’coalescence’according to urban growth phase theory.This study provides urban planners with relevant insights for the urban expansion characteristics of West Africa.
基金supported by the National Natural Science Foundation of China project(Grant No.41661144022)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA19030203),the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2020VTA0001),and the MOST High-Level Foreign Expert program(Grant No.GL20200161002).
文摘Human activities modulate the impact of environmental forcing in general and of climate in particular.Information on the spatial and temporal patterns of human activities is in high demand,but scarce in sparsely populated and data-poor regions such as Northern Africa.The intensity and spatial distribution of nighttime lights provide useful information on human activities and can be observed by space-borne imaging radiometers.Our study helps to bridge the gap between the DMSP-OLS data available until 2013 and the NPP-VIIRS data available since 2013.The approach to calibrate the OLS data includes three steps:a)inter-calibrate the OLS DN data acquired by different sensors in 1992-2013;b)cali-brate the OLS DN data using VIIRS data in 2013;c)generate syn-thetic OLS radiance data by degrading the VIIRS data in 2013-2020.We generated a)a time series of calibrated OLS nighttime light radiance data(1992-2013);b)mean annual VIIRS radiance on stable lights at the OLS spatial resolution for 2013-2020;c)synthetic OLS radiance data generated using VIIRS radiance data degraded to match the radiometric specifications of OLS for 2013-2020.The evaluation of these data products in 2013 documented their accu-racy and consistency.
文摘在全球变暖和人类活动的背景下,降水在年内分布上发生了比较大的变化,对人民生产生活产生了巨大的影响,这一影响在城市化较高的地区尤为明显。基于多源降水数据(降水产品数据和气象站点数据)和夜间灯光数据,选定中国的长三角城市群作为研究区域,将基尼系数(Gini Index,GI)作为降水集中度的指标,利用Theil-Sen Median斜率估计和Mann-Kendall显著性检验进行趋势分析,最后通过相关性分析探究城市化程度与降水集中度的关系。研究结果表明:(1)CHIRPS(Climate Hazards Group InfraRed Precipitation with Station Data)数据计算得到的GI与站点数据结果的均方根误差为0.036,远小于CMFD数据(0.067)和MSWEP数据(0.083)的结果,表明CHIRPS数据具有最佳的适用性;(2)长三角城市群的降水不均匀性从南向北逐渐增加,并在城市群中部和西部呈现出显著上升的趋势,研究区域内的降水年内分布将会朝着集中分布的方向发展,极端降水事件出现的可能性增加;(3)城市化对降水集中度主要起到促进作用,城市的快速发展使得降水不均匀性增强,并且在城市群内的南京市、无锡市和镇江市等地区更为显著,更有可能发生城市内涝等灾害。研究对于城市的防洪设计、城市道路排水管道的设计和城市防洪应急响应预案的编制具有参考意义。
