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This article aims to evaluate impact of image saturation on radiometric intercalibration of Defense Meteorological Satellite Program's Operational Linescan System (DMSP/OLS) stable nighttime light (NTL) images. We simulated two sets of stable NTL images, one with saturation and the other without saturation, by using DMSP/OLS radiance calibrated images without saturation. For each dataset, we intercalibrated the simulated images of seven years using a quadratic regression model. We found that the saturation-derived difference of the radiometric intercalibration is more obvious in areas where the digital number value is higher than a certain value (e.g., ∼30). By comparing the calibrated images of the two datasets, we found that the absolute value of the saturation-derived relative bias of the intercalibration tends to be positively correlated to the ratio of saturated pixels in the calibration field, with Pearson correlation of 0.4610 (
Hanrui Cao; Xi Li; Zhe Tong. Impact of Image Saturation on Radiometric Intercalibration of DMSP/OLS Nighttime Light Images. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2021, 14, 7948 -7960.
AMA StyleHanrui Cao, Xi Li, Zhe Tong. Impact of Image Saturation on Radiometric Intercalibration of DMSP/OLS Nighttime Light Images. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2021; 14 ():7948-7960.
Chicago/Turabian StyleHanrui Cao; Xi Li; Zhe Tong. 2021. "Impact of Image Saturation on Radiometric Intercalibration of DMSP/OLS Nighttime Light Images." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 14, no. : 7948-7960.
The lockdown of cities against the COVID-19 epidemic directly decreases urban socioeconomic activities. Remotely sensed night-time light (NTL) provides a macro perspective to capture these variations. Here, taking 20 global megacities as examples, we adopted the NASA’s Black Marble NTL data with a daily resolution to investigate their spatio-temporal changes. We collected daily NTL products for four weeks (one month) before and after the date of lockdown in each city, which were then summarized as weekly and monthly averaged NTL images after pre-processing (cloud removing, outlier detection, etc.). Results show that NTL overall decreased after the lockdown of cities, but with regional disparities and varying spatial patterns. Asian cities experienced the most obvious reduction of NTL. Particularly, the monthly averaged NTL in Mumbai, India, decreased by nearly 20% compared to one month before. However, there was no significant decline in NTL in European cities. African cities also experienced stable changes of NTL. Spatially, city centers darkened more obviously than the urban periphery. Facing emergencies, NTL data has broad applications in monitoring socioeconomic dynamics and assessing public policies in a near real-time manner.
Gang Xu; Tianyu Xiu; Xi Li; Xinlian Liang; Limin Jiao. Lockdown Induced Night-Time Light Dynamics during the COVID-19 Epidemic in Global Megacities. International Journal of Applied Earth Observation and Geoinformation 2021, 102, 102421 -102421.
AMA StyleGang Xu, Tianyu Xiu, Xi Li, Xinlian Liang, Limin Jiao. Lockdown Induced Night-Time Light Dynamics during the COVID-19 Epidemic in Global Megacities. International Journal of Applied Earth Observation and Geoinformation. 2021; 102 ():102421-102421.
Chicago/Turabian StyleGang Xu; Tianyu Xiu; Xi Li; Xinlian Liang; Limin Jiao. 2021. "Lockdown Induced Night-Time Light Dynamics during the COVID-19 Epidemic in Global Megacities." International Journal of Applied Earth Observation and Geoinformation 102, no. : 102421-102421.
High spatiotemporal population data are critical for a wide range of applications (e.g. urban planning and management, risk assessment, and epidemic control). However, such data are still not widely available due to the limited knowledge of complex human activities. Here we proposed a spatiotemporal downscaling framework for estimating hourly population dynamics in Beijing by integrating remote sensing and social sensing data. First, we generated two baseline maps of population during sleep and work times using a dasymetric method. Second, we generated urban functional zones using a random forest model and derived human activity patterns from social sensing data. Finally, we estimated the hourly population dynamics at a 500-meter resolution using a temporal downscaling method. Results show the significant spatial difference of the population over time, especially between working hours (9:00 − 18:00) and sleeping hours (after 0:00). The spatial pattern of population is more homogenous within the sixth ring area in Beijing during work time compared to sleep time when there are more clusters of high population. The comparison of spatiotemporal patterns with the referenced real-time heat maps from Baidu indicates that our population data are reliable. The framework presented in this paper is transferable in other regions. The resulting dataset of hourly population dynamics is of great help for governments of emergency responses as well as for studies about human risks to environmental issues.
Xia Zhao; Yuyu Zhou; Wei Chen; Xi Li; Xuecao Li; Deren Li. Mapping hourly population dynamics using remotely sensed and geospatial data: a case study in Beijing, China. GIScience & Remote Sensing 2021, 58, 717 -732.
AMA StyleXia Zhao, Yuyu Zhou, Wei Chen, Xi Li, Xuecao Li, Deren Li. Mapping hourly population dynamics using remotely sensed and geospatial data: a case study in Beijing, China. GIScience & Remote Sensing. 2021; 58 (5):717-732.
Chicago/Turabian StyleXia Zhao; Yuyu Zhou; Wei Chen; Xi Li; Xuecao Li; Deren Li. 2021. "Mapping hourly population dynamics using remotely sensed and geospatial data: a case study in Beijing, China." GIScience & Remote Sensing 58, no. 5: 717-732.
The further scientific applications of DMSP-OLS night-time light (NTL) imagery have been being limited by the accuracy, automation and speed of radiometric intercalibration. In order to solve the aforementioned problems, this paper is the first to propose a new least-median-of-squares (LMedS)-based power regression (LBPR) for automatically radiometric intercalibration, and investigate the reasons of the optimal model of radiometric intercalibration, especially those based on the Taylor expansion and probability principle. NTL data in six different global regions, from 1998 to 2007, were used as the test datasets. When the five kinds of LMedS-based radiometric intercalibration models (i.e., linear, quadratic, power, exponential and logarithmic regression) are synthetically compared in absolute accuracy (adjusted RMSE) and running speed, it is concluded that the LBPR, which has the highest accuracy and preferable running speed, is recommended as the optimal method, which can also be used as a reference for other types of imagery pre-processing.
Chang Li; Xi Li; Tian Li; Qi Meng; Wenjie Yu. LMedS-Based Power Regression: An Optimal and Automatic Method of Radiometric Intercalibration for DMSP-OLS NTL Imagery. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2021, 14, 2046 -2057.
AMA StyleChang Li, Xi Li, Tian Li, Qi Meng, Wenjie Yu. LMedS-Based Power Regression: An Optimal and Automatic Method of Radiometric Intercalibration for DMSP-OLS NTL Imagery. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2021; 14 (99):2046-2057.
Chicago/Turabian StyleChang Li; Xi Li; Tian Li; Qi Meng; Wenjie Yu. 2021. "LMedS-Based Power Regression: An Optimal and Automatic Method of Radiometric Intercalibration for DMSP-OLS NTL Imagery." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 14, no. 99: 2046-2057.
Current automatic shadow compensation methods often suffer because their contrast improvement processes are not self-adaptive and, consequently, the results they produce do not adequately represent the real objects. The study presented in this paper designed a new automatic shadow compensation framework based on improvements to the Wallis principle, which included an intensity coefficient and a stretching coefficient to enhance contrast and brightness more efficiently. An automatic parameter calculation strategy also is a part of this framework, which is based on searching for and matching similar feature points around shadow boundaries. Finally, a final compensation combination strategy combines the regional compensation with the local window compensation of the pixels in each shadow to improve the shaded information in a balanced way. All these strategies in our method work together to provide a better measurement for customizing suitable compensation depending on the condition of each region and pixel. The intensity component I also is automatically strengthened through the customized compensation model. Color correction is executed in a way that avoids the color bias caused by over-compensated component values, thereby better reflecting shaded information. Images with clouds shadows and ground objects shadows were utilized to test our method and six other state-of-the-art methods. The comparison results indicate that our method compensated for shaded information more effectively, accurately, and evenly than the other methods for customizing suitable models for each shadow and pixel with reasonable time-cost. Its brightness, contrast, and object color in shaded areas were approximately equalized with non-shaded regions to present a shadow-free image.
Yuanwei Yang; Shuhao Ran; Xianjun Gao; Mingwei Wang; Xi Li. An Automatic Shadow Compensation Method via a New Model Combined Wallis Filter with LCC Model in High Resolution Remote Sensing Images. Applied Sciences 2020, 10, 5799 .
AMA StyleYuanwei Yang, Shuhao Ran, Xianjun Gao, Mingwei Wang, Xi Li. An Automatic Shadow Compensation Method via a New Model Combined Wallis Filter with LCC Model in High Resolution Remote Sensing Images. Applied Sciences. 2020; 10 (17):5799.
Chicago/Turabian StyleYuanwei Yang; Shuhao Ran; Xianjun Gao; Mingwei Wang; Xi Li. 2020. "An Automatic Shadow Compensation Method via a New Model Combined Wallis Filter with LCC Model in High Resolution Remote Sensing Images." Applied Sciences 10, no. 17: 5799.
Luojia-1 satellite is a new launched night-time light satellite providing 130 m resolution images. To evaluate the additional spatial details of Luojia-1 compared to VIIRS images, we employed road network analysis to compare the two kinds of images in Los Angeles, United States. In the road network analysis, we calculated the correlation coefficients between the distance to the primary road and the image radiance in 228 neighborhood areas, and we found that the average Spearman correlation coefficient is −0.3843 for Luojia-1 and −0.0974 for VIIRS, while those of the Pearson correlation coefficients are −0.3129 and −0.1370, respectively. In addition, we also calculated the Pearson correlation coefficients between the distance to the road intersections and the image radiance, and the average coefficient for Luojia-1 is −0.2967 and that of the VIIRS is −0.1100. The road network analysis suggests that the night-time light radiance in Luojia-1 is stronger correlated to the road network than VIIRS. All these findings show that Luojia-1 images provide richer information to reflect urban structures than VIIRS, indicating that Luojia-1 images have potential for studying urban socioeconomic parameters at a fine resolution.
Huimin Xu; Xi Li. Evaluating Spatial Details of Luojia-1 Night-Time Images Using Road Network Analysis. Communications in Computer and Information Science 2020, 122 -131.
AMA StyleHuimin Xu, Xi Li. Evaluating Spatial Details of Luojia-1 Night-Time Images Using Road Network Analysis. Communications in Computer and Information Science. 2020; ():122-131.
Chicago/Turabian StyleHuimin Xu; Xi Li. 2020. "Evaluating Spatial Details of Luojia-1 Night-Time Images Using Road Network Analysis." Communications in Computer and Information Science , no. : 122-131.
Satellite-observed night-time light in urban areas has been widely used as an indicator for socioeconomic development and light pollution. Up to present, the diurnal dynamics of city light during the night, which are important to understand the nature of human activity and the underlying variables explaining night-time brightness, have hardly been investigated by remote sensing techniques due to limitation of the revisit time and spatial resolution of available satellites. In this study, we employed a consumer-grade unmanned aerial vehicle (UAV) to monitor city light in a study area located in Wuhan City, China, from 8:08 PM, April 15, 2019 to 5:08 AM, April 16, 2019, with an hourly temporal resolution. By using three ground-based Sky Quality Meters (SQMs), we found that the UAV-recorded light brightness was consistent with the ground luminous intensity measured by the SQMs in both the spatial (R2 = 0.72) and temporal dimensions (R2 > 0.94), and that the average city light brightness was consistent with the sky brightness in the temporal dimension (R2 = 0.98), indicating that UAV images can reliably monitor the city's night-time brightness. The temporal analysis showed that different locations had different patterns of temporal changes in their night-time brightness, implying that inter-calibration of two kinds of satellite images with different overpass times would be a challenge. Combining an urban function map of 18 classes and the hourly UAV images, we found that urban functions differed in their temporal light dynamics. For example, the outdoor sports field lost 97.28% of its measured brightness between 8: 08 PM – 4:05 AM, while an administrative building only lost 4.56%, and the entire study area lost 61.86% of its total brightness. Within our study area, the period between 9:06 PM and 10:05 PM was the period with largest amount of light loss. The spectral analysis we conducted showed that city light colors were different in some urban functions, with the major road being the reddest region at 8:08 PM and becoming even redder at 4:05 AM. This preliminary study indicates that UAVs are a good tool to investigate city light at night, and that city light is very complex in both of the temporal and spatial dimensions, requiring comprehensive investigation using more advanced UAV techniques, and emphasizing the need for geostationary platforms for night-time light sensors.
Xi Li; Noam Levin; Jinlong Xie; Deren Li. Monitoring hourly night-time light by an unmanned aerial vehicle and its implications to satellite remote sensing. Remote Sensing of Environment 2020, 247, 111942 .
AMA StyleXi Li, Noam Levin, Jinlong Xie, Deren Li. Monitoring hourly night-time light by an unmanned aerial vehicle and its implications to satellite remote sensing. Remote Sensing of Environment. 2020; 247 ():111942.
Chicago/Turabian StyleXi Li; Noam Levin; Jinlong Xie; Deren Li. 2020. "Monitoring hourly night-time light by an unmanned aerial vehicle and its implications to satellite remote sensing." Remote Sensing of Environment 247, no. : 111942.
The lack of official statistics makes it difficult to assess Venezuela's economic situation during the socioeconomic crisis. In this study, we used Visible Infrared Imaging Radiometer Suite (VIIRS) nighttime light images to evaluate Venezuela's crisis. The Hodrick—Prescott filter was used to decompose the sum of urban light (SUL) into two components, the sum of urban light trend (SULT) and the sum of urban light cycle. Then we proposed an index of nighttime light change ratio (NLCR) to estimate Venezuelan nighttime light dynamics. We found that Venezuela has lost 30.37% of its SULT from April 2012 to December 2018. The regression analysis shows that Venezuelan SULT had a strong relationship to a number of socioeconomic indicators: the SULT is positively correlated to crude oil production with R $^2$ of 0.9159, and negatively correlated to dollar exchange rate with R $^2$ of 0.9516, and negatively correlated to the number of asylum seekers with R2 of 0.8384. We also found that among the three states with largest nighttime light decrease, economy of two states was dominated by agriculture and that of one state was dominated by the oil industry. In the pixel analysis, compared with the urban cores, the suburbs of urban cores of 12 main cities have a higher percentage of SULT-increased areas. Around the Venezuela-Colombia border, the SULT decreased in the Venezuelan side but increased in the Colombian side. Our analysis suggests that nighttime light imagery can help to assess Venezuela's situation during the crisis.
Lin Zhang; Xi Li; Fengrui Chen. Spatiotemporal Analysis of Venezuela's Nighttime Light During the Socioeconomic Crisis. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2020, 13, 2396 -2408.
AMA StyleLin Zhang, Xi Li, Fengrui Chen. Spatiotemporal Analysis of Venezuela's Nighttime Light During the Socioeconomic Crisis. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2020; 13 (99):2396-2408.
Chicago/Turabian StyleLin Zhang; Xi Li; Fengrui Chen. 2020. "Spatiotemporal Analysis of Venezuela's Nighttime Light During the Socioeconomic Crisis." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 13, no. 99: 2396-2408.
Urban connectivity information is important for regional planning of sustainable development goals. However, there are still challenges in deriving the spatial connectivity relationship among urban areas. The nighttime light data measures anthropogenic phenomenon remotely and can be seen as a unique source for monitoring urban spatial expansion and human activities. This study presents an object-based approach for investigating spatial connectivity among urban patches by incorporating Suomi National Polar-orbiting Partnership Visible Infrared Imaging Radiometer Suite Day/Night Band (NPP-VIIRS) and land use data collected in 2015. A graph-based method is used to construct connectivity networks, and explore spatial patterns considering both quantity and quality of connections in three vibrant urban agglomerations in China, namely, Jing-Jin-Ji (JJJ), Yangtze River Delta (YRD), and Pearl River Delta (PRD) megaregions. Results indicate that networks follow a power law distribution according to cumulative degree distributions. A closer connectivity relationship exists among urban patches in PRD, with a relatively high intensity connection ratio and a mean degree of 4.5, compared with YRD and JJJ. Block-like connections are observed in core areas of all UAs, and single-tree connections are found in peripheral areas. This study implies a significant inequality in the regional development and hub-spoke structures with hubs of provincial capitals and municipalities. Our proposed framework is transferrable for the analysis of connectivity relationship in other regions and the outcome can contribute to the study of evolution of urban agglomerations, and bring insights to policymakers for sustainable development at regional level.
Xia Zhao; Xi Li; Yuyu Zhou; Deren Li. Analyzing Urban Spatial Connectivity Using Night Light Observations: A Case Study of Three Representative Urban Agglomerations in China. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2020, 13, 1097 -1108.
AMA StyleXia Zhao, Xi Li, Yuyu Zhou, Deren Li. Analyzing Urban Spatial Connectivity Using Night Light Observations: A Case Study of Three Representative Urban Agglomerations in China. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2020; 13 (99):1097-1108.
Chicago/Turabian StyleXia Zhao; Xi Li; Yuyu Zhou; Deren Li. 2020. "Analyzing Urban Spatial Connectivity Using Night Light Observations: A Case Study of Three Representative Urban Agglomerations in China." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 13, no. 99: 1097-1108.
Night-time light (NTL) images have been proved as a type of reliable data source to map urban expansion. In this paper, to investigate the potential of using multi-source NTL images at near 100 m resolution to detect urban expansion, we use a Luojia1-01 (LJ1-01) image in 2018 and an International Space Station (ISS) night-time image in 2010 in Wuhan city as experiment images. Based on the multiple linear robust regression model, a process of intercalibration between LJ1-01 imagery and ISS imagery is proposed to build a comparable dataset. To detect urban expansion, using the above images at 130 m resolution, Jeffries-Matusita distance is used as an indicator to select the feature combination with the largest class separability. Among all the candidate combinations, the combination of the LJ1-01 image, the simulated LJ1-01 image, and their ratio best meets our requirements for classification. With this feature combination, a multi-temporal classification method based on Support Vector Machines and Back Propagating (BP) – Neural Network, respectively, is utilized to classify the study area into stable non-urban class, stable urban class, and expanding the urban class. The results of the multi-temporal classification show that the overall accuracy is around 90%, and the Kappa coefficients are larger than 0.84. For each class, the user’s accuracy is larger than 87%, and the producer’s accuracy is larger than 83%. The results of this study indicate that it is feasible to detect urban expansion by using multi-source NTL images at near 100 m resolution.
Zimin Yin; Xi Li; Fei Tong; Zhibiao Li; Michael Jendryke. Mapping urban expansion using night-time light images from Luojia1-01 and International Space Station. International Journal of Remote Sensing 2019, 41, 2603 -2623.
AMA StyleZimin Yin, Xi Li, Fei Tong, Zhibiao Li, Michael Jendryke. Mapping urban expansion using night-time light images from Luojia1-01 and International Space Station. International Journal of Remote Sensing. 2019; 41 (7):2603-2623.
Chicago/Turabian StyleZimin Yin; Xi Li; Fei Tong; Zhibiao Li; Michael Jendryke. 2019. "Mapping urban expansion using night-time light images from Luojia1-01 and International Space Station." International Journal of Remote Sensing 41, no. 7: 2603-2623.
Night-time light (NTL) data shows a high correspondence with human activities. Recent studies also found that the NTL responds to holidays, and that light values often peak at festival times. However, there are few studies on the different patterns of light change caused by different cultural events. Here, we examined the impacts of festivals on NTL, examining both the seasonal changes in NTL, and the spatial patterns of NTL changes during festivals. The monthly Visual Near-Infrared band composites on Suomi National Polar-orbiting Partnership (Suomi NPP VIIRS) from January 2014 to December 2017 were used. Firstly, we studied two religious events, Ramadan in Mecca, Saudi Arabia, and Ashura in Najaf, Iraq. We extracted the seasonal changes using a Seasonal-Trend decomposition procedure based on Loess and a proposed Information Ratio (IR) index, and found two completely different light change patterns, which corresponded to two Islamic factions, Shia and Sunni. Secondly, we studied two kinds of celebrations, Carnival and a catholic religious event (Day of the Virgin of Guadalupe), in Cancún and Puebla City in Mexico and found the distribution of light change during festivals is clearly distinguished between carnival and the religious event. The NTL during Carnival increases uniformly throughout the city, while the NTL during religious event presented an aggregate increase centring on the central cathedral. Thirdly, we calculated the Information Ratio (IR) values at the pixel scale and analysed the spatial distribution of seasonality in the four regions, Mecca and Najaf showing different patterns of light change during the event months compared to Mexico areas. The analysis shows that different characteristics of different cultures can be distinguished through the spatio-temporal analysis of NTL data. Given the responses of NTL to cultural context, local knowledge should be incorporated to better understand how people modify the nightscape.
Shanshan Liu; Xi Li; Noam Levin; Michael Jendryke. Tracing cultural festival patterns using time-series of VIIRS monthly products. Remote Sensing Letters 2019, 10, 1172 -1181.
AMA StyleShanshan Liu, Xi Li, Noam Levin, Michael Jendryke. Tracing cultural festival patterns using time-series of VIIRS monthly products. Remote Sensing Letters. 2019; 10 (12):1172-1181.
Chicago/Turabian StyleShanshan Liu; Xi Li; Noam Levin; Michael Jendryke. 2019. "Tracing cultural festival patterns using time-series of VIIRS monthly products." Remote Sensing Letters 10, no. 12: 1172-1181.
Luojia 1-01 satellite, launched on 2 June 2018, provides a new data source of nighttime light at 130 m resolution and shows potential for mapping urban extent. In this paper, using Luojia 1-01 and VIIRS nighttime light imagery, we compared several methods for extracting urban areas, including Human Settlement Index (HSI), Simple Thresholding Segmentation (STS) and SVM supervised classification. According to the accuracy assessment, the HSI method using LJ1-01 data had the best performance in urban extent extraction, which presented the largest Kappa Coefficient value, 0.834, among all the results. For the urban areas extracted by VIIRS based HSI method, the largest Kappa Coefficient value was 0.772. In contrast, the largest Kappa Coefficient values obtained by STS method were 0.79 and 0.7512 respectively when using LJ1-01 and VIIRS data, while for SVM method the values were 0.7829 and 0.7486 when using Landsat-LJ and Landsat-VIIRS composite data respectively. The experimented results demonstrated that the utilization of nighttime light imagery can largely improve the accuracy of urban extent extraction and LJ1-01 data, with a higher resolution and more abundant spatial information, can lead to better identification results than its predecessors.
Xi Li; Lixian Zhao; Deren Li; Huimin Xu. Mapping Urban Extent Using Luojia 1-01 Nighttime Light Imagery. Sensors 2018, 18, 3665 .
AMA StyleXi Li, Lixian Zhao, Deren Li, Huimin Xu. Mapping Urban Extent Using Luojia 1-01 Nighttime Light Imagery. Sensors. 2018; 18 (11):3665.
Chicago/Turabian StyleXi Li; Lixian Zhao; Deren Li; Huimin Xu. 2018. "Mapping Urban Extent Using Luojia 1-01 Nighttime Light Imagery." Sensors 18, no. 11: 3665.
In this study, we analyzed the night-time light dynamics in Iraq over the period 2012–2017 by using Visible Infrared Imaging Radiometer Suite (VIIRS) monthly composites. The data quality of VIIRS images was improved by repairing the missing data, and the Night-time Light Ratio Indices (NLRIs), derived from urban extent map and night-time light images, were calculated for different provinces and cities. We found that when the Islamic State of Iraq and Syria (ISIS) attacked or occupied a region, the region lost its light rapidly, with the provinces of Al-Anbar, At-Ta’min, Ninawa, and Sala Ad-din losing 63%, 73%, 88%, and 56%, of their night-time light, respectively, between December 2013 and December 2014. Moreover, the light returned after the Iraqi Security Forces (ISF) recaptured the region. In addition, we also found that the night-time light in the Kurdish Autonomous Region showed a steady decline after 2014, with the Arbil, Dihok, and As-Sulaymaniyah provinces losing 47%, 18%, and 31% of their night-time light between December 2013 and December 2016 as a result of the economic crisis in the region. The night-time light in Southern Iraq, the region controlled by Iraqi central government, has grown continuously; for example, the night-time light in Al Basrah increased by 75% between December 2013 and December 2017. Regions formerly controlled by ISIS experienced a return of night-time light during 2017 as the ISF retook almost all this territory in 2017. This indicates that as reconstruction began, electricity was re-supplied in these regions. Our analysis shows the night-time light in Iraq is directly linked to the socioeconomic dynamics of Iraq, and demonstrates that the VIIRS monthly night-time light images are an effective data source for tracking humanitarian disasters in that country.
Xi Li; Shanshan Liu; Michael Jendryke; Deren Li; Chuanqing Wu. Night-Time Light Dynamics during the Iraqi Civil War. Remote Sensing 2018, 10, 858 .
AMA StyleXi Li, Shanshan Liu, Michael Jendryke, Deren Li, Chuanqing Wu. Night-Time Light Dynamics during the Iraqi Civil War. Remote Sensing. 2018; 10 (6):858.
Chicago/Turabian StyleXi Li; Shanshan Liu; Michael Jendryke; Deren Li; Chuanqing Wu. 2018. "Night-Time Light Dynamics during the Iraqi Civil War." Remote Sensing 10, no. 6: 858.
In this paper, we conducted a scientometric analysis based on the Night-Time Light (NTL) remote sensing related literature datasets retrieved from Science Citation Index Expanded and Social Science Citation Index in Web of Science core collection database. Using the methods of bibliometric and Social Network Analysis (SNA), we drew several conclusions: (1) NTL related studies have become a research hotspot, especially after 2011 when the second generation of NTL satellites, the Suomi National Polar-orbiting Partnership (S-NPP) Satellite with the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor was on board. In the same period, the open-access policy of the long historical dataset of the first generation satellite Defense Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS) started. (2) Most related studies are conducted by authors from USA and China, and the USA takes the lead in the field. We identified the biggest research communities constructed by co-authorships and the related important authors and topics by SNA. (3) By the visualization and analysis of the topic evolution using the co-word and co-cited reference networks, we can clearly see that: the research topics change from hardware oriented studies to more real-world applications; and from the first generation of the satellite DMSP/OLS to the second generation of satellite S-NPP. Although the Day Night Band (DNB) of the S-NPP exhibits higher spatial and radiometric resolution and better calibration conditions than the first generation DMSP/OLS, the longer historical datasets in DMSP/OLS are still important in long-term and large-scale human activity analysis. (4) In line with the intuitive knowledge, the NTL remote sensing related studies display stronger connections (such as interpretive frame, context, and academic purpose) to the social sciences than the general remote sensing discipline. The citation trajectories are visualized based on the dual-maps, thus the research preferences for combining the environmental, ecological, economic, and political science disciplines are clearly exhibited. Overall, the picture of the NTL remote sensing research is presented from the scientist-level, topic-level, and discipline-level interactions. Based on these analyses, we also discuss the possible trends in the future work, such as combining NTL studies with social science research and social media data.
Kai Hu; Kunlun Qi; Qingfeng Guan; Chuanqing Wu; Jingmin Yu; Yaxian Qing; Jie Zheng; Huayi Wu; Xi Li. A Scientometric Visualization Analysis for Night-Time Light Remote Sensing Research from 1991 to 2016. Remote Sensing 2017, 9, 802 .
AMA StyleKai Hu, Kunlun Qi, Qingfeng Guan, Chuanqing Wu, Jingmin Yu, Yaxian Qing, Jie Zheng, Huayi Wu, Xi Li. A Scientometric Visualization Analysis for Night-Time Light Remote Sensing Research from 1991 to 2016. Remote Sensing. 2017; 9 (8):802.
Chicago/Turabian StyleKai Hu; Kunlun Qi; Qingfeng Guan; Chuanqing Wu; Jingmin Yu; Yaxian Qing; Jie Zheng; Huayi Wu; Xi Li. 2017. "A Scientometric Visualization Analysis for Night-Time Light Remote Sensing Research from 1991 to 2016." Remote Sensing 9, no. 8: 802.
Xi Li; Christopher Elvidge; Yuyu Zhou; Changyong Cao; Timothy Warner. Remote sensing of night-time light. International Journal of Remote Sensing 2017, 38, 5855 -5859.
AMA StyleXi Li, Christopher Elvidge, Yuyu Zhou, Changyong Cao, Timothy Warner. Remote sensing of night-time light. International Journal of Remote Sensing. 2017; 38 (21):5855-5859.
Chicago/Turabian StyleXi Li; Christopher Elvidge; Yuyu Zhou; Changyong Cao; Timothy Warner. 2017. "Remote sensing of night-time light." International Journal of Remote Sensing 38, no. 21: 5855-5859.
Monthly composites of night-time light acquired from the Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS) had been used to evaluate socio-economic dynamics and human rights during the Syrian Civil War, which started in March 2011. However, DMSP/OLS monthly composites are not available subsequent to February 2014, and the only available night-time light composites for that period were acquired from the Suomi National Polar-orbiting Partnership satellite’s Visible Infrared Imaging Radiometer Suite (Suomi NPP/VIIRS). This article proposes an intercalibration model to simulate DMSP/OLS composites from the VIIRS day-and-night band (DNB) composites, by using a power function for radiometric degradation and a Gaussian low pass filter for spatial degradation. The DMSP/OLS data and the simulated DMSP/OLS data were combined to estimate the city light dynamics in Syria’s major human settlement between March 2011 and January 2017. Our analysis shows that Syria’s major human settlement lost about 79% of its city light by January 2017, with Aleppo, Daraa, Deir ez-Zor, and Idlib provinces losing 89%, 90%, 96%, and 99% of their light, respectively, indicating that these four provinces were most affected by the war. We also found that the city light in Syria and 12 provinces rebounded from early 2016 to January 2017, possibly as a result of the peace negotiation signed in Geneva.
Xi Li; Deren Li; Huimin Xu; Chuanqing Wu. Intercalibration between DMSP/OLS and VIIRS night-time light images to evaluate city light dynamics of Syria’s major human settlement during Syrian Civil War. International Journal of Remote Sensing 2017, 38, 5934 -5951.
AMA StyleXi Li, Deren Li, Huimin Xu, Chuanqing Wu. Intercalibration between DMSP/OLS and VIIRS night-time light images to evaluate city light dynamics of Syria’s major human settlement during Syrian Civil War. International Journal of Remote Sensing. 2017; 38 (21):5934-5951.
Chicago/Turabian StyleXi Li; Deren Li; Huimin Xu; Chuanqing Wu. 2017. "Intercalibration between DMSP/OLS and VIIRS night-time light images to evaluate city light dynamics of Syria’s major human settlement during Syrian Civil War." International Journal of Remote Sensing 38, no. 21: 5934-5951.
As the successor of the Tropical Rainfall Measuring Mission (TRMM), the Global Precipitation Measurement (GPM) mission significantly improves the spatial resolution of precipitation estimates from 0.25° to 0.1°. The present study analyzed the error structures of Integrated Multisatellite Retrievals for GPM (IMERG) monthly precipitation products over Mainland China from March 2014 to February 2015 using gauge measurements at multiple spatiotemporal scales. Moreover, IMERG products were also compared with TRMM 3B43 products. The results show that: (1) overall, IMERG can capture the spatial patterns of precipitation over China well. It performs a little better than TRMM 3B43 at seasonal and monthly scales; (2) the performance of IMERG varies greatly spatially and temporally. IMERG performs better at low latitudes than at middle latitudes, and shows worse performance in winter than at other times; (3) compared with TRMM 3B43, IMERG significantly improves the estimation accuracy of precipitation over the Xinjiang region and the Qinghai-Tibetan Plateau, especially over the former where IMERG increases Pearson correlation coefficient by 0.18 and decreases root-mean-square error by 54.47 mm for annual precipitation estimates. However, most IMERG products over these areas are unreliable; and (4) IMERG shows poor performance in winter as TRMM 3B43 even if GPM improved its ability to sense frozen precipitation. Most of them over North China are unreliable during this period.
Fengrui Chen; Xi Li. Evaluation of IMERG and TRMM 3B43 Monthly Precipitation Products over Mainland China. Remote Sensing 2016, 8, 472 .
AMA StyleFengrui Chen, Xi Li. Evaluation of IMERG and TRMM 3B43 Monthly Precipitation Products over Mainland China. Remote Sensing. 2016; 8 (6):472.
Chicago/Turabian StyleFengrui Chen; Xi Li. 2016. "Evaluation of IMERG and TRMM 3B43 Monthly Precipitation Products over Mainland China." Remote Sensing 8, no. 6: 472.
City lights, fishing boats, and oil fields are the major sources of nighttime lights, therefore the nighttime light images provide a unique source to map human beings and their activities from outer space. While most of the scholars focused on application of nighttime light remote sensing in urbanization and regional development, the actual fields are much wider. This paper summarized the applications of nighttime light remote sensing into fields such as the estimation of socioeconomic parameters, monitoring urbanization, evaluation of important events, analyzing light pollution, fishery, etc. For estimation of socioeconomic parameters, the most promising progress is that Gross Domestic Product and its growth rate have been estimated with statistical data and nighttime light data using econometric models. For monitoring urbanization, urban area and its dynamics can be extracted using different classification methods, and spatial analysis has been employed to map urban agglomeration. As sharp changes of nighttime light are associated with important socioeconomic events, the images have been used to evaluate humanitarian disasters, especially in the current Syrian and Iraqi wars. Light pollution is another hotspot of nighttime light application, as the night light is related to some diseases and abnormal behavior of animals, and the nighttime light images can provide light pollution information on large scales so that it is much easier to analyze the effects of light pollutions. In each field, we listed typical cases of the applications. At last, future studies of nighttime light remote sensing have been predicted.
Deren Li; Xia Zhao; Xi Li. Remote sensing of human beings – a perspective from nighttime light. Geo-spatial Information Science 2016, 19, 69 -79.
AMA StyleDeren Li, Xia Zhao, Xi Li. Remote sensing of human beings – a perspective from nighttime light. Geo-spatial Information Science. 2016; 19 (1):69-79.
Chicago/Turabian StyleDeren Li; Xia Zhao; Xi Li. 2016. "Remote sensing of human beings – a perspective from nighttime light." Geo-spatial Information Science 19, no. 1: 69-79.
This study used the Night Light Development Index (NLDI) to measure the regional inequality of public services in Mainland China at multiple scales. The NLDI was extracted based on a Gini Coefficient approach to measure the spatial differences of population distribution and night light distribution. Population data were derived from the dataset of China’s population density grid, and night light data were acquired from satellite imagery. In the multi-scale analysis, we calculated the NLDI for China as a whole, eight economic regions, 31 provincial regions, and 354 prefectural cities for the two years of 2005 and 2010. The results indicate that Southwest China and Northwest China are the regions with the most unequal public services, with NLDI values of 0.7116 and 0.7251 for 2005, respectively, and 0.6678 and 0.6304 for 2010, respectively. In contrast, Northern Coastal China had the lowest NLDI values of 0.4775 and 0.4312 for 2005 and 2010, respectively, indicating that this region had the most equal public services. Also, the regional inequality of Mainland China in terms of NLDI has been reduced from 0.6161 to 0.5743 during 2005–2010. The same pattern was observed from the provincial and prefectural analysis, suggesting that public services in Mainland China became more equal within the five-year period. A regression analysis indicated that provincial and prefectural regions with more public services per capita and higher population density had more equal public services.
Huimin Xu; Hutao Yang; Xi Li; Huiran Jin; Deren Li. Multi-Scale Measurement of Regional Inequality in Mainland China during 2005–2010 Using DMSP/OLS Night Light Imagery and Population Density Grid Data. Sustainability 2015, 7, 13469 -13499.
AMA StyleHuimin Xu, Hutao Yang, Xi Li, Huiran Jin, Deren Li. Multi-Scale Measurement of Regional Inequality in Mainland China during 2005–2010 Using DMSP/OLS Night Light Imagery and Population Density Grid Data. Sustainability. 2015; 7 (10):13469-13499.
Chicago/Turabian StyleHuimin Xu; Hutao Yang; Xi Li; Huiran Jin; Deren Li. 2015. "Multi-Scale Measurement of Regional Inequality in Mainland China during 2005–2010 Using DMSP/OLS Night Light Imagery and Population Density Grid Data." Sustainability 7, no. 10: 13469-13499.
This study investigates whether night-time light images acquired from the Defense Meteorological Satellite Program’s Operational Linescan System provide spatial and temporal insight with regard to the humanitarian aspects of the Syrian crisis. Evaluating the ongoing crisis in Syria is challenging since reliable witness reports are hard to gather in a war zone. Therefore satellite images, as one of the few sources of objective information, are potentially of great importance. We used 38 monthly Defense Meteorological Satellite Program’s Operational Linescan System composites covering the period between January 2008 and February 2014. The results indicate that night-time light and lit area in Syria declined by about 74% and 73%, respectively, between March 2011 and February 2014. In 12 of 14 provinces, night-time light declined by >60%. Damascus and Quneitra are the exceptions, with night-time light having declined only by about 35%. Notably, the number of internally displaced persons (IDPs) of each province shows a linear correlation with night-time light loss, with an R2 value of 0.52. Through clustering the time series images, we found that the international border of Syria represents a distinct boundary between regions of differing night-time light spatiotemporal patterns. The contrast across the border increases as the region studied encompasses a wider zone on either side of the border. These findings lend support to the hypothesis that night-time light can be a useful source for monitoring humanitarian crises such as that unfolding in Syria.
Xi Li; Deren Li. Can night-time light images play a role in evaluating the Syrian Crisis? International Journal of Remote Sensing 2014, 35, 6648 -6661.
AMA StyleXi Li, Deren Li. Can night-time light images play a role in evaluating the Syrian Crisis? International Journal of Remote Sensing. 2014; 35 (18):6648-6661.
Chicago/Turabian StyleXi Li; Deren Li. 2014. "Can night-time light images play a role in evaluating the Syrian Crisis?" International Journal of Remote Sensing 35, no. 18: 6648-6661.