Geolocating social media users aims to discover the real geographical locations of users from their publicly available data,which can support online location-based applications such as disaster alerts and local conten...Geolocating social media users aims to discover the real geographical locations of users from their publicly available data,which can support online location-based applications such as disaster alerts and local content recommen-dations.Social relationship-based methods represent a classical approach for geolocating social media.However,geographically proximate relationships are sparse and challenging to discern within social networks,thereby affecting the accuracy of user geolocation.To address this challenge,we propose user geolocation methods that integrate neighborhood geographical distribution and social structure influence(NGSI)to improve geolocation accuracy.Firstly,we propose a method for evaluating the homophily of locations based on the k-order neighbor-hood geographic distribution(k-NGD)similarity among users.There are notable differences in the distribution of k-NGD similarity between location-proximate and non-location-proximate users.Exploiting this distinction,we filter out non-location-proximate social relationships to enhance location homophily in the social network.To better utilize the location-proximate relationships in social networks,we propose a graph neural network algorithm based on the social structure influence.The algorithm enables us to perform a weighted aggregation of the information of users’multi-hop neighborhood,thereby mitigating the over-smoothing problem of user features and improving user geolocation performance.Experimental results on real social media dataset demonstrate that the neighborhood geographical distribution similarity metric can effectively filter out non-location-proximate social relationships.Moreover,compared with 7 existing social relationship-based user positioning methods,our proposed method can achieve multi-granularity user geolocation and improve the accuracy by 4.84%to 13.28%.展开更多
Stereo synthetic aperture radar （SAR） geolocation model is an important geolocation model for spaceborne SAR. However, the error of stereo SAR geolocation model has not been analyzed in detail. This paper deduced th...Stereo synthetic aperture radar （SAR） geolocation model is an important geolocation model for spaceborne SAR. However, the error of stereo SAR geolocation model has not been analyzed in detail. This paper deduced the geolocation error formulas of the stereo SAR geolocation model and then compared the geolocation error with range Doppler （RD） geolocation model. Through computer simulation, we could get the advantages and disadvantages of the stereo SAR geolocation model.展开更多
Existing IP geolocation algorithms based on delay similarity often rely on the principle that geographically adjacent IPs have similar delays.However,this principle is often invalid in real Internet environment,which ...Existing IP geolocation algorithms based on delay similarity often rely on the principle that geographically adjacent IPs have similar delays.However,this principle is often invalid in real Internet environment,which leads to unreliable geolocation results.To improve the accuracy and reliability of locating IP in real Internet,a street-level IP geolocation algorithm based on landmarks clustering is proposed.Firstly,we use the probes to measure the known landmarks to obtain their delay vectors,and cluster landmarks using them.Secondly,the landmarks are clustered again by their latitude and longitude,and the intersection of these two clustering results is taken to form training sets.Thirdly,we train multiple neural networks to get the mapping relationship between delay and location in each training set.Finally,we determine one of the neural networks for the target by the delay similarity and relative hop counts,and then geolocate the target by this network.As it brings together the delay and geographical coordinates clustering,the proposed algorithm largely improves the inconsistency between them and enhances the mapping relationship between them.We evaluate the algorithm by a series of experiments in Hong Kong,Shanghai,Zhengzhou and New York.The experimental results show that the proposed algorithm achieves street-level IP geolocation,and comparing with existing typical streetlevel geolocation algorithms,the proposed algorithm improves the geolocation reliability significantly.展开更多
The Beijing Swift(Apus apus pekinensis)is a typical cavity-nesting bird that often nests inside holes and crevices in old architectures.Direct observation of their breeding behaviour is challenging and their breeding ...The Beijing Swift(Apus apus pekinensis)is a typical cavity-nesting bird that often nests inside holes and crevices in old architectures.Direct observation of their breeding behaviour is challenging and their breeding ecology is thus poorly studied.In this study,we analysed light-level geolocation data collected from six Beijing Swifts for the first time.Our results showed that geolocators can make comprehensive inference of their incubation period and behaviour.As a cost-effective and non-invasive method,geolocators can not only facilitate discovering migration routes,but also can be widely applied in the study of avian reproductive behaviour,especially in cavity-nesting bird species.We further discussed the characteristics and merits of this method and compared with other conventional nest-monitoring methods in recording birds.展开更多
A novel statistical angle-of-arrival (AOA) model for indoor geolocation applications is presented. The modeling approach focuses on the arrivals of the multipath components with respect to the line-of-sight (LOS) path...A novel statistical angle-of-arrival (AOA) model for indoor geolocation applications is presented. The modeling approach focuses on the arrivals of the multipath components with respect to the line-of-sight (LOS) path which is an important component especially when indoor geolocation applications are considered. The model is particularly important for indoor applications where AOA information could be utilized for tracking indirect paths to aid in precise ranging in harsh and dense multipath environments where LOS path might be blocked due to obstructions. The results have been obtained by a measurement calibrated ray-tracing (RT) tool.展开更多
Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of fact...Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of factors, such as errors in the measurement of signal parameters, uncertainties regarding the position of satellites, and errors in the location of calibration sources, are known to degrade the accuracy of target localization in satellite geolocation systems. We systematically analyze the performance of multi-satellite joint geolocation based on time difference of arrival （TDOA） measurements. The theoretical analysis starts with Cramer Rao bound （CRB） derivations for four localization scenarios under an altitude constraint and Gaussian noise assumption. In scenario 1, only the TDOA measurement errors of the emitting source are considered and the satellite positions are assumed to be perfectly estimated. In scenario 2, both the TDOA measurement errors and satellite position uncertainties are taken into account. Scenario 3 assumes that some calibration sources with accurate position information are used to mitigate the influence of satellite position perturbations. In scenario 4, several calibration sources at inaccurate locations are used to alleviate satellite position errors in target localization. Through comparing the CRBs of the four localization scenarios, some valuable＇s insights are gained into the effects of various error sources on the estimation performance. Two kinds of location mean-square errors （MSE） expressions under the altitude constraint are derived through first-order perturbation analysis and the Lagrange method. The first location MSE provides the theoretical prediction when an estimator assumes that the satellite locations are accurate but in fact have errors. The second location MSE provides the localization accuracy if an estimator assumes that the known calibration source locations are precise while in fact erroneous. Simulation results are included to verify the theoretical analysis.展开更多
The Moon is a potential new platform for Earth observation.The advantages of its large-scale observational scope,long temporal duration,and multi-layer detecting of the Earth will undoubtedly advance our understanding...The Moon is a potential new platform for Earth observation.The advantages of its large-scale observational scope,long temporal duration,and multi-layer detecting of the Earth will undoubtedly advance our understanding of the Earth system.To carry out the observations from a Moon-based optical sensor,the geolocation error caused by exterior orientation elements need to be investigated.This paper analyses the error effects of exterior orientation elements on geolocation for an optical sensor.To estimate the error,we present a geometric image model and utilise some parameters to measure the image offsets.Through a large number of numerical simulations,the results demonstrate that the image offsets are not obvious influenced by the distance and observation angle at mid-high latitude of the Moon and have linear correlation with the increasing errors of the exterior orientation elements.Further,the relationship between the spatial resolution and errors of exterior orientation elements are revealed.Finally,the error characteristics for Moon-based Earth observation are discussed.It is expected that the conclusion drawn in this paper could support the study of a Moon-based Earth observation optical sensor.展开更多
One of the greatest feats of avian migration is the non-stop crossing of extensive areas of inhospitable habitat such as deserts and seas. Differences in spring and autumn migration routes have been reported in specie...One of the greatest feats of avian migration is the non-stop crossing of extensive areas of inhospitable habitat such as deserts and seas. Differences in spring and autumn migration routes have been reported in species that cross such barriers, and are thought to have evolved in response to seasonal variation in prevailing wind direction. We tested the hypothesis that migration routes vary seasonally with respect to the Gulf of Mexico in the tree swallow Tachycineta bicolor using solar geolocators attached and retrieved at 4 breeding sites in central North America. We found that 100 % of birds （n = 10） made a trans-Gulf flight of 〉850 km from Louisiana south to their wintering grounds in the Yucatan Peninsula in 12-36 hours, achieving minimum ground speeds as high as 32 m/s. Although most days during autumn migration were characterized by unfavorable headwinds blowing to the northwest, migration over the Gulf mostly occurred on days with strong winds blowing to the south. In contrast, in 8 of 9 （88 %） birds on spring migration returned from the wintering grounds towards Louisiana following a clockwise loop pat- tern flying over land to the west around the Gulf. During this spring period there were few days with prevailing winds from the south to assist northward migration. Results suggest that, despite being up to three times further （ca. 2,700 kin）, a coastal circum-Gulf spring migration represents the less risky route when wind conditions are not favorable. These findings also help to resolve a long-standing dispute in the literature concerning migration patterns between the US Gulf coast and Mexico, and provide insight into the factors shaping migration strategies of small songbirds migrating across large bodies of water [Current Zoology 60（5）： 653-559, 2014].展开更多
Although many classical IP geolocation algorithms are suitable to rich-connected networks, their performances are seriously affected in poor-connected networks with weak delay-distance correlation. This paper tries to...Although many classical IP geolocation algorithms are suitable to rich-connected networks, their performances are seriously affected in poor-connected networks with weak delay-distance correlation. This paper tries to improve the performances of classical IP geolocation algorithms by finding rich-connected sub-networks inside poor-connected networks. First, a new delay-distance correlation model （RTD-Corr model） is proposed. It builds the relationship between delay-distance correlation and actual network factors such as the tortuosity of the network path and the ratio of propagation delay. Second, based on the RTD-Corr model and actual network characteristics, this paper discusses about how to find rich-connected networks inside China Intemet which is a typical actual poor-connected network. Then we find rich-connected sub-networks of China Intemet through a large-scale network measurement which covers three major ISPs and thirty provinces. At last, based on the founded rich-connected sub-networks, we modify two classical IP geolocation algorithms and the experiments in China Intemet show that their accuracy is significantly increased.展开更多
TerraSAR-X(TSX)can acquire high-resolution SAR images and due to its high orbit precision as well as its ability to acquire data from different off-nadir viewing angles,the high-precision stereo geolocation can be obt...TerraSAR-X(TSX)can acquire high-resolution SAR images and due to its high orbit precision as well as its ability to acquire data from different off-nadir viewing angles,the high-precision stereo geolocation can be obtained.In this study,we investigate the absolute geolocation accuracy of TSX high-resolution images in Wuhan,China.We present a direct stereo SAR geolocation method and analyze the 2D and 3D geoposition accuracy of two corner reflectors.The sub-meter localization accuracy was achieved using only atmospheric correction information available in the TSX metadata.展开更多
Location based services(LBS)are widely utilized,and determining the location of users’IP is the foundation for LBS.Constrained by unstable delay and insufficient landmarks,the existing geolocation algorithms have pro...Location based services(LBS)are widely utilized,and determining the location of users’IP is the foundation for LBS.Constrained by unstable delay and insufficient landmarks,the existing geolocation algorithms have problems such as low geolocation accuracy and uncertain geolocation error,difficult to meet the requirements of LBS for accuracy and reliability.A new IP geolocation algorithm based on router error training is proposed in this manuscript to improve the accuracy of geolocation results and obtain the current geolocation error range.Firstly,bootstrapping is utilized to divide the landmark data into training set and verification set,and/24 subnet distribution is utilized to extend the training set.Secondly,the path detection is performed on nodes in the three data sets respectively to extract the metropolitan area network(MAN)of the target city,and the geolocation result and error of each router in MAN are obtained by training the detection results.Finally,the MAN is utilized to get the target’s location.Based on China’s 24,254 IP geolocation experiments,the proposed algorithm has higher geolocation accuracy and lower median error than existing typical geolocation algorithms LBG,SLG,NNG and RNBG,and in most cases the difference is less than 10km between estimated error and actual error.展开更多
Birds exhibit a high degree of migratory diversity,which is influenced by various ecological factors and life history strategies.Conducting studies on tropical bird migration,of which research is scarce,and comparing ...Birds exhibit a high degree of migratory diversity,which is influenced by various ecological factors and life history strategies.Conducting studies on tropical bird migration,of which research is scarce,and comparing it with temperate birds can enhance our understanding of bird migration behaviour and its underlying mecha-nisms.In this study,we explored the migration behaviour of a breeding population of the Barn Swallow(Hirundo rustica)in Zhanjiang,southern China,a region located in the northern tropics,using light-level geolocators.From 2021 to 2023,we deployed geolocators on 92 breeding swallows and retrieved geolocators successfully from 23 individuals.These swallows all exhibited migratory behaviour,and wintering on various islands in Southeast Asia.They displayed sex differences in their wintering locations.All males concentrated in Borneo,while females primarily chose Borneo but also dispersed to the Philippines,South China Sea,and Vietnam for wintering.The studied swallow population adopted a seasonal migration pattern of“indirect in autumn,direct in spring”,bypassing the ecological barrier of the South China Sea in autumn and tending to directly cross it in spring migration.Moreover,the distance and duration of autumn migration was significantly longer than those of the spring migration.Compared to temperate Barn Swallows,the Barn Swallow population breeding in Zhanjiang adopts a pattern of“intra-tropical migration”and initiates autumn migration earlier.The formation of their migration pattern may be limited by ecological and physiological factors.展开更多
High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to ana...High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to analyze it in a 3D environment and understand its intricate role as the Water Tower of Asia.The science teams of NASA realized an 8-m DEM using satellite stereo imagery for HMA,termed HMA 8-m DEM.In this research,we assessed the vertical accuracy of HMA 8-m DEM using reference elevations from ICESat-2 geolocated photons at three test sites of varied topography and land covers.Inferences were made from statistical quantifiers and elevation profiles.For the world’s highest mountain,Mount Everest,and its surroundings,Root Mean Squared Error(RMSE)and Mean Absolute Error(MAE)resulted in 1.94 m and 1.66 m,respectively;however,a uniform positive bias observed in the elevation profiles indicates the seasonal snow cover change will dent the accurate estimation of the elevation in this sort of test sites.The second test site containing gentle slopes with forest patches has exhibited the Digital Surface Model(DSM)features with RMSE and MAE of 0.58 m and 0.52 m,respectively.The third test site,situated in the Zanda County of the Qinghai-Tibet,is a relatively flat terrain bed,mostly bare earth with sudden river cuts,and has minimal errors with RMSE and MAE of 0.32 m and 0.29 m,respectively,and with a negligible bias.Additionally,in one more test site,the feasibility of detecting the glacial lakes was tested,which resulted in exhibiting a flat surface over the surface of the lakes,indicating the potential of HMA 8-m DEM for deriving the hydrological parameters.The results accrued in this investigation confirm that the HMA 8-m DEM has the best vertical accuracy and should be of high use for analyzing natural hazards and monitoring glacier surfaces.展开更多
For the high-resolution airborne synthetic aperture radar （SAR） stereo geolocation application, the final geolocation ac- curacy is influenced by various error parameter sources. In this paper, an airborne SAR stere...For the high-resolution airborne synthetic aperture radar （SAR） stereo geolocation application, the final geolocation ac- curacy is influenced by various error parameter sources. In this paper, an airborne SAR stereo geolocation parameter error model, involving the parameter errors derived from the navigation system on the flight platform, has been put forward. Moreover, a kind of near-direct method for modeling and sensitivity analysis of navigation parameter errors is also given. This method directly uses the ground reference to calculate the covariance matrix relationship between the parameter errors and the eventual geoloeation errors for ground target points. In addition, utilizing true flight track parameters＇ errors, this paper gave a verification of the method and a corresponding sensitivity analysis for airborne SAR stereo geolocation model and proved its efficiency.展开更多
IP geolocation determines geographical location by the IP address of Internet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much mor...IP geolocation determines geographical location by the IP address of Internet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much more attentions in these years since more and more physical devices are connected to cyberspace.Most geolocation methods cannot resolve the geolocation accuracy for those devices with few landmarks around.In this paper,we propose a novel geolocation approach that is based on common routers as secondary landmarks(Common Routers-based Geolocation,CRG).We search plenty of common routers by topology discovery among web server landmarks.We use statistical learning to study localized(delay,hop)-distance correlation and locate these common routers.We locate the accurate positions of common routers and convert them as secondary landmarks to help improve the feasibility of our geolocation system in areas that landmarks are sparsely distributed.We manage to improve the geolocation accuracy and decrease the maximum geolocation error compared to one of the state-of-the-art geolocation methods.At the end of this paper,we discuss the reason of the efficiency of our method and our future research.展开更多
IP geolocation determines geographical location by the IP address of Internet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much mor...IP geolocation determines geographical location by the IP address of Internet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much more attentions in these years since more and more physical devices are connected to cyberspace.Most geolocation methods cannot resolve the geolocation accuracy for those devices with few landmarks around.In this paper,we propose a novel geolocation approach that is based on common routers as secondary landmarks(Common Routers-based Geolocation,CRG).We search plenty of common routers by topology discovery among web server landmarks.We use statistical learning to study localized(delay,hop)-distance correlation and locate these common routers.We locate the accurate positions of common routers and convert them as secondary landmarks to help improve the feasibility of our geolocation system in areas that landmarks are sparsely distributed.We manage to improve the geolocation accuracy and decrease the maximum geolocation error compared to one of the state-of-the-art geolocation methods.At the end of this paper,we discuss the reason of the efficiency of our method and our future research.展开更多
基金This work was supported by the National Key R&D Program of China(No.2022YFB3102904)the National Natural Science Foundation of China(No.62172435,U23A20305)Key Research and Development Project of Henan Province(No.221111321200).
文摘Geolocating social media users aims to discover the real geographical locations of users from their publicly available data,which can support online location-based applications such as disaster alerts and local content recommen-dations.Social relationship-based methods represent a classical approach for geolocating social media.However,geographically proximate relationships are sparse and challenging to discern within social networks,thereby affecting the accuracy of user geolocation.To address this challenge,we propose user geolocation methods that integrate neighborhood geographical distribution and social structure influence(NGSI)to improve geolocation accuracy.Firstly,we propose a method for evaluating the homophily of locations based on the k-order neighbor-hood geographic distribution(k-NGD)similarity among users.There are notable differences in the distribution of k-NGD similarity between location-proximate and non-location-proximate users.Exploiting this distinction,we filter out non-location-proximate social relationships to enhance location homophily in the social network.To better utilize the location-proximate relationships in social networks,we propose a graph neural network algorithm based on the social structure influence.The algorithm enables us to perform a weighted aggregation of the information of users’multi-hop neighborhood,thereby mitigating the over-smoothing problem of user features and improving user geolocation performance.Experimental results on real social media dataset demonstrate that the neighborhood geographical distribution similarity metric can effectively filter out non-location-proximate social relationships.Moreover,compared with 7 existing social relationship-based user positioning methods,our proposed method can achieve multi-granularity user geolocation and improve the accuracy by 4.84%to 13.28%.
基金Project supported by the Shanghai Leading Academic Discipline Project (Grant No.S30108)the National Natural Science Foundation of China (Grant No.61071185)+1 种基金the Key Technology Research and Development Program of Science and Technology Commission of Shanghai Municipality (Grant No.10511501702)the Science and Technology Commission of Shanghai Municipality (Grant Nos.08590700500, 08DZ2231100)
文摘Stereo synthetic aperture radar （SAR） geolocation model is an important geolocation model for spaceborne SAR. However, the error of stereo SAR geolocation model has not been analyzed in detail. This paper deduced the geolocation error formulas of the stereo SAR geolocation model and then compared the geolocation error with range Doppler （RD） geolocation model. Through computer simulation, we could get the advantages and disadvantages of the stereo SAR geolocation model.
基金the National Key R&D Program of China 2016YFB0801303(F.L.received the grant,the sponsors’website is https://service.most.gov.cn/)by the National Key R&D Program of China 2016QY01W0105(X.L.received the grant,the sponsors’website is https://service.most.gov.cn/)+5 种基金by the National Natural Science Foundation of China U1636219(X.L.received the grant,the sponsors’website is http://www.nsfc.gov.cn/)by the National Natural Science Foundation of China 61602508(J.L.received the grant,the sponsors’website is http://www.nsfc.gov.cn/)by the National Natural Science Foundation of China 61772549(F.L.received the grant,the sponsors’website is http://www.nsfc.gov.cn/)by the National Natural Science Foundation of China U1736214(F.L.received the grant,the sponsors’website is http://www.nsfc.gov.cn/)by the National Natural Science Foundation of China U1804263(X.L.received the grant,the sponsors’website is http://www.nsfc.gov.cn/)by the Science and Technology Innovation Talent Project of Henan Province 184200510018(X.L.received the grant,the sponsors’website is http://www.hnkjt.gov.cn/).
文摘Existing IP geolocation algorithms based on delay similarity often rely on the principle that geographically adjacent IPs have similar delays.However,this principle is often invalid in real Internet environment,which leads to unreliable geolocation results.To improve the accuracy and reliability of locating IP in real Internet,a street-level IP geolocation algorithm based on landmarks clustering is proposed.Firstly,we use the probes to measure the known landmarks to obtain their delay vectors,and cluster landmarks using them.Secondly,the landmarks are clustered again by their latitude and longitude,and the intersection of these two clustering results is taken to form training sets.Thirdly,we train multiple neural networks to get the mapping relationship between delay and location in each training set.Finally,we determine one of the neural networks for the target by the delay similarity and relative hop counts,and then geolocate the target by this network.As it brings together the delay and geographical coordinates clustering,the proposed algorithm largely improves the inconsistency between them and enhances the mapping relationship between them.We evaluate the algorithm by a series of experiments in Hong Kong,Shanghai,Zhengzhou and New York.The experimental results show that the proposed algorithm achieves street-level IP geolocation,and comparing with existing typical streetlevel geolocation algorithms,the proposed algorithm improves the geolocation reliability significantly.
基金funded by SHAN SHUI Conservation Centre,Beijing。
文摘The Beijing Swift(Apus apus pekinensis)is a typical cavity-nesting bird that often nests inside holes and crevices in old architectures.Direct observation of their breeding behaviour is challenging and their breeding ecology is thus poorly studied.In this study,we analysed light-level geolocation data collected from six Beijing Swifts for the first time.Our results showed that geolocators can make comprehensive inference of their incubation period and behaviour.As a cost-effective and non-invasive method,geolocators can not only facilitate discovering migration routes,but also can be widely applied in the study of avian reproductive behaviour,especially in cavity-nesting bird species.We further discussed the characteristics and merits of this method and compared with other conventional nest-monitoring methods in recording birds.
文摘A novel statistical angle-of-arrival (AOA) model for indoor geolocation applications is presented. The modeling approach focuses on the arrivals of the multipath components with respect to the line-of-sight (LOS) path which is an important component especially when indoor geolocation applications are considered. The model is particularly important for indoor applications where AOA information could be utilized for tracking indirect paths to aid in precise ranging in harsh and dense multipath environments where LOS path might be blocked due to obstructions. The results have been obtained by a measurement calibrated ray-tracing (RT) tool.
基金Project supported by the National Natural Science Foundation of China （No. 61201381）, the Future Development Foundation of Zhengzhou Information Science and Technology Institute （No. YPI2JJ202057）, China Postdoctoral Science Foundation （No. 2016M592989）, and the Outstanding Youth Foundation of Information Engineering University （No. 2016603201）
文摘Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of factors, such as errors in the measurement of signal parameters, uncertainties regarding the position of satellites, and errors in the location of calibration sources, are known to degrade the accuracy of target localization in satellite geolocation systems. We systematically analyze the performance of multi-satellite joint geolocation based on time difference of arrival （TDOA） measurements. The theoretical analysis starts with Cramer Rao bound （CRB） derivations for four localization scenarios under an altitude constraint and Gaussian noise assumption. In scenario 1, only the TDOA measurement errors of the emitting source are considered and the satellite positions are assumed to be perfectly estimated. In scenario 2, both the TDOA measurement errors and satellite position uncertainties are taken into account. Scenario 3 assumes that some calibration sources with accurate position information are used to mitigate the influence of satellite position perturbations. In scenario 4, several calibration sources at inaccurate locations are used to alleviate satellite position errors in target localization. Through comparing the CRBs of the four localization scenarios, some valuable＇s insights are gained into the effects of various error sources on the estimation performance. Two kinds of location mean-square errors （MSE） expressions under the altitude constraint are derived through first-order perturbation analysis and the Lagrange method. The first location MSE provides the theoretical prediction when an estimator assumes that the satellite locations are accurate but in fact have errors. The second location MSE provides the localization accuracy if an estimator assumes that the known calibration source locations are precise while in fact erroneous. Simulation results are included to verify the theoretical analysis.
基金supported by the National Natural Science Foundation of China[Grant No.41590852]the Key Research Program of Frontier Sciences,CAS[Grant No.QYZDY-SSW-DQC026]the Director Graduate Student Foundation of Institute of Remote Sensing and Digital Earth,Chinese Academy of Sciences[Grant No.Y7SY1400CX].
文摘The Moon is a potential new platform for Earth observation.The advantages of its large-scale observational scope,long temporal duration,and multi-layer detecting of the Earth will undoubtedly advance our understanding of the Earth system.To carry out the observations from a Moon-based optical sensor,the geolocation error caused by exterior orientation elements need to be investigated.This paper analyses the error effects of exterior orientation elements on geolocation for an optical sensor.To estimate the error,we present a geometric image model and utilise some parameters to measure the image offsets.Through a large number of numerical simulations,the results demonstrate that the image offsets are not obvious influenced by the distance and observation angle at mid-high latitude of the Moon and have linear correlation with the increasing errors of the exterior orientation elements.Further,the relationship between the spatial resolution and errors of exterior orientation elements are revealed.Finally,the error characteristics for Moon-based Earth observation are discussed.It is expected that the conclusion drawn in this paper could support the study of a Moon-based Earth observation optical sensor.
文摘One of the greatest feats of avian migration is the non-stop crossing of extensive areas of inhospitable habitat such as deserts and seas. Differences in spring and autumn migration routes have been reported in species that cross such barriers, and are thought to have evolved in response to seasonal variation in prevailing wind direction. We tested the hypothesis that migration routes vary seasonally with respect to the Gulf of Mexico in the tree swallow Tachycineta bicolor using solar geolocators attached and retrieved at 4 breeding sites in central North America. We found that 100 % of birds （n = 10） made a trans-Gulf flight of 〉850 km from Louisiana south to their wintering grounds in the Yucatan Peninsula in 12-36 hours, achieving minimum ground speeds as high as 32 m/s. Although most days during autumn migration were characterized by unfavorable headwinds blowing to the northwest, migration over the Gulf mostly occurred on days with strong winds blowing to the south. In contrast, in 8 of 9 （88 %） birds on spring migration returned from the wintering grounds towards Louisiana following a clockwise loop pat- tern flying over land to the west around the Gulf. During this spring period there were few days with prevailing winds from the south to assist northward migration. Results suggest that, despite being up to three times further （ca. 2,700 kin）, a coastal circum-Gulf spring migration represents the less risky route when wind conditions are not favorable. These findings also help to resolve a long-standing dispute in the literature concerning migration patterns between the US Gulf coast and Mexico, and provide insight into the factors shaping migration strategies of small songbirds migrating across large bodies of water [Current Zoology 60（5）： 653-559, 2014].
基金Supported by the National Natural Science Foundation of China(61379151,61274189,61302159 and 61401512)the Excellent Youth Foundation of Henan Province of China(144100510001)Foundation of Science and Technology on Information Assurance Laboratory(KJ-14-108)
文摘Although many classical IP geolocation algorithms are suitable to rich-connected networks, their performances are seriously affected in poor-connected networks with weak delay-distance correlation. This paper tries to improve the performances of classical IP geolocation algorithms by finding rich-connected sub-networks inside poor-connected networks. First, a new delay-distance correlation model （RTD-Corr model） is proposed. It builds the relationship between delay-distance correlation and actual network factors such as the tortuosity of the network path and the ratio of propagation delay. Second, based on the RTD-Corr model and actual network characteristics, this paper discusses about how to find rich-connected networks inside China Intemet which is a typical actual poor-connected network. Then we find rich-connected sub-networks of China Intemet through a large-scale network measurement which covers three major ISPs and thirty provinces. At last, based on the founded rich-connected sub-networks, we modify two classical IP geolocation algorithms and the experiments in China Intemet show that their accuracy is significantly increased.
基金This work was supported by the National Natural Science Foundation of China[grant number 61331016]and[grant number 41174120].The TerraSAR-X data were provided by DLR via the LAN2245 Project.
文摘TerraSAR-X(TSX)can acquire high-resolution SAR images and due to its high orbit precision as well as its ability to acquire data from different off-nadir viewing angles,the high-precision stereo geolocation can be obtained.In this study,we investigate the absolute geolocation accuracy of TSX high-resolution images in Wuhan,China.We present a direct stereo SAR geolocation method and analyze the 2D and 3D geoposition accuracy of two corner reflectors.The sub-meter localization accuracy was achieved using only atmospheric correction information available in the TSX metadata.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.U1804263,U1636219)the Science and Technology Innovation Talent Project of Henan Province(184200510018)Zhongyuan Science and Technology Innovation Leading Talent Project(214200510019).
文摘Location based services(LBS)are widely utilized,and determining the location of users’IP is the foundation for LBS.Constrained by unstable delay and insufficient landmarks,the existing geolocation algorithms have problems such as low geolocation accuracy and uncertain geolocation error,difficult to meet the requirements of LBS for accuracy and reliability.A new IP geolocation algorithm based on router error training is proposed in this manuscript to improve the accuracy of geolocation results and obtain the current geolocation error range.Firstly,bootstrapping is utilized to divide the landmark data into training set and verification set,and/24 subnet distribution is utilized to extend the training set.Secondly,the path detection is performed on nodes in the three data sets respectively to extract the metropolitan area network(MAN)of the target city,and the geolocation result and error of each router in MAN are obtained by training the detection results.Finally,the MAN is utilized to get the target’s location.Based on China’s 24,254 IP geolocation experiments,the proposed algorithm has higher geolocation accuracy and lower median error than existing typical geolocation algorithms LBG,SLG,NNG and RNBG,and in most cases the difference is less than 10km between estimated error and actual error.
基金supported by the National Natural Science Foundation of China(32101236,32270518)National Key R&D Program of China(2022YFF0802400).
文摘Birds exhibit a high degree of migratory diversity,which is influenced by various ecological factors and life history strategies.Conducting studies on tropical bird migration,of which research is scarce,and comparing it with temperate birds can enhance our understanding of bird migration behaviour and its underlying mecha-nisms.In this study,we explored the migration behaviour of a breeding population of the Barn Swallow(Hirundo rustica)in Zhanjiang,southern China,a region located in the northern tropics,using light-level geolocators.From 2021 to 2023,we deployed geolocators on 92 breeding swallows and retrieved geolocators successfully from 23 individuals.These swallows all exhibited migratory behaviour,and wintering on various islands in Southeast Asia.They displayed sex differences in their wintering locations.All males concentrated in Borneo,while females primarily chose Borneo but also dispersed to the Philippines,South China Sea,and Vietnam for wintering.The studied swallow population adopted a seasonal migration pattern of“indirect in autumn,direct in spring”,bypassing the ecological barrier of the South China Sea in autumn and tending to directly cross it in spring migration.Moreover,the distance and duration of autumn migration was significantly longer than those of the spring migration.Compared to temperate Barn Swallows,the Barn Swallow population breeding in Zhanjiang adopts a pattern of“intra-tropical migration”and initiates autumn migration earlier.The formation of their migration pattern may be limited by ecological and physiological factors.
基金The authors gratefully acknowledge the science teams of NASA High Mountain Asia 8-meter DEM and NASA ICESat-2 for providing access to the data.This work was conducted with the infrastructure provided by the National Remote Sensing Centre(NRSC),for which the authors were indebted to the Director,NRSC,Hyderabad.We acknowledge the continued support and scientific insights from Mr.Rakesh Fararoda,Mr.Sagar S Salunkhe,Mr.Hansraj Meena,Mr.Ashish K.Jain and other staff members of Regional Remote Sensing Centre-West,NRSC/ISRO,Jodhpur.The authors want to acknowledge Dr.Kamal Pandey,Scientist,IIRS,Dehradun,for sharing field-level information about the Auli-Joshimath.This research did not receive any specific grant from funding agencies in the public,commercial,or not-for-profit sectors.
文摘High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to analyze it in a 3D environment and understand its intricate role as the Water Tower of Asia.The science teams of NASA realized an 8-m DEM using satellite stereo imagery for HMA,termed HMA 8-m DEM.In this research,we assessed the vertical accuracy of HMA 8-m DEM using reference elevations from ICESat-2 geolocated photons at three test sites of varied topography and land covers.Inferences were made from statistical quantifiers and elevation profiles.For the world’s highest mountain,Mount Everest,and its surroundings,Root Mean Squared Error(RMSE)and Mean Absolute Error(MAE)resulted in 1.94 m and 1.66 m,respectively;however,a uniform positive bias observed in the elevation profiles indicates the seasonal snow cover change will dent the accurate estimation of the elevation in this sort of test sites.The second test site containing gentle slopes with forest patches has exhibited the Digital Surface Model(DSM)features with RMSE and MAE of 0.58 m and 0.52 m,respectively.The third test site,situated in the Zanda County of the Qinghai-Tibet,is a relatively flat terrain bed,mostly bare earth with sudden river cuts,and has minimal errors with RMSE and MAE of 0.32 m and 0.29 m,respectively,and with a negligible bias.Additionally,in one more test site,the feasibility of detecting the glacial lakes was tested,which resulted in exhibiting a flat surface over the surface of the lakes,indicating the potential of HMA 8-m DEM for deriving the hydrological parameters.The results accrued in this investigation confirm that the HMA 8-m DEM has the best vertical accuracy and should be of high use for analyzing natural hazards and monitoring glacier surfaces.
基金Supported by the National Basic Research Program of China (No. 2006CB701303)
文摘For the high-resolution airborne synthetic aperture radar （SAR） stereo geolocation application, the final geolocation ac- curacy is influenced by various error parameter sources. In this paper, an airborne SAR stereo geolocation parameter error model, involving the parameter errors derived from the navigation system on the flight platform, has been put forward. Moreover, a kind of near-direct method for modeling and sensitivity analysis of navigation parameter errors is also given. This method directly uses the ground reference to calculate the covariance matrix relationship between the parameter errors and the eventual geoloeation errors for ground target points. In addition, utilizing true flight track parameters＇ errors, this paper gave a verification of the method and a corresponding sensitivity analysis for airborne SAR stereo geolocation model and proved its efficiency.
文摘IP geolocation determines geographical location by the IP address of Internet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much more attentions in these years since more and more physical devices are connected to cyberspace.Most geolocation methods cannot resolve the geolocation accuracy for those devices with few landmarks around.In this paper,we propose a novel geolocation approach that is based on common routers as secondary landmarks(Common Routers-based Geolocation,CRG).We search plenty of common routers by topology discovery among web server landmarks.We use statistical learning to study localized(delay,hop)-distance correlation and locate these common routers.We locate the accurate positions of common routers and convert them as secondary landmarks to help improve the feasibility of our geolocation system in areas that landmarks are sparsely distributed.We manage to improve the geolocation accuracy and decrease the maximum geolocation error compared to one of the state-of-the-art geolocation methods.At the end of this paper,we discuss the reason of the efficiency of our method and our future research.
文摘IP geolocation determines geographical location by the IP address of Internet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much more attentions in these years since more and more physical devices are connected to cyberspace.Most geolocation methods cannot resolve the geolocation accuracy for those devices with few landmarks around.In this paper,we propose a novel geolocation approach that is based on common routers as secondary landmarks(Common Routers-based Geolocation,CRG).We search plenty of common routers by topology discovery among web server landmarks.We use statistical learning to study localized(delay,hop)-distance correlation and locate these common routers.We locate the accurate positions of common routers and convert them as secondary landmarks to help improve the feasibility of our geolocation system in areas that landmarks are sparsely distributed.We manage to improve the geolocation accuracy and decrease the maximum geolocation error compared to one of the state-of-the-art geolocation methods.At the end of this paper,we discuss the reason of the efficiency of our method and our future research.
