Multi-dimensional, long-term time series displacement monitoring is crucial for generating early warnings for active landslides and for mitigating geohazards. The synthetic aperture radar(SAR) interferometry method ha...Multi-dimensional, long-term time series displacement monitoring is crucial for generating early warnings for active landslides and for mitigating geohazards. The synthetic aperture radar(SAR) interferometry method has been widely applied to achieve small-gradient landslide displacement monitoring;however, measuring the landslide displacement with a steep gradient has posed certain challenges. In comparison, the SAR offset tracking method is a powerful tool for mapping large-gradient landslide displacement in both the slant-range and azimuth directions. Nevertheless, there are some limitations in the existing SAR offset tracking approaches:(i) the measurement accuracy is greatly reduced by the extreme topography relief in high mountain areas,(ii) a fixed matching window from expert experience is usually adopted in the calculation of cross-correlation,(iii) estimating the long-term displacements between the SAR images from cross-platforms and with longer spatiotemporal baselines is a challenging task, and(iv) it is difficult to calculate the three-dimensional(3D) landslide displacements using a single SAR dataset.Additionally, only a few studies have focused on how to realize early warning of landslide deformation using SAR measurements.To address these issues, this paper presents an improved cross-platform SAR offset tracking method, which can not only estimate high-precision landslide displacements in two and three dimensions but also calculate long-term time series displacements over a decade using cross-platform SAR offset tracking measurements. Initially, we optimize the traditional SAR offset tracking workflow to estimate high-precision ground displacements, in which three improvements are highlighted:(i) an“ortho-rectification” operation is applied to restrain the effect of topography relief,(ii) an “adaptive matching window” is adopted in the cross-correlation computation, and(iii) a new strategy is proposed to combine all the possible offset pairs and optimally design the displacement inversion network based on the “optimization theory” of geodetic inversion. Next, robust mathematical equations are built to estimate the two-dimensional(2D) and 3D long-term time series landslide displacements using cross-platform SAR observations. The M-estimator is introduced into the 2D displacement inversion equation to restrain the outliers, and the total least squares criterion is adopted to estimate the 3D displacements considering the random errors in both the design matrix and observations. We take the Laojingbian landslide, Wudongde Reservoir Area(China), as an example to demonstrate the proposed method using ALOS/PALSAR-1 and ALOS/PALSAR-2 images. The results reveal that the proposed method significantly outperforms traditional methods. We also retrieve the movement direction of each pixel of the Laojingbian landslide using the proposed method, thus allowing us to understand the fine-scale landslide kinematics. Finally, we capture and analyze the acceleration characteristics of the landslide, perform an early warning of hazard, and forecast the future displacement evolution based on the 3D displacement time series coupled with the physical models of the rocks.展开更多
COSMO-SkyMed is a constellation of four X-band high-resolution radar satellites with a minimum revisit period of 12 hours.These satellites can obtain ascending and descending synthetic aperture radar(SAR)images with v...COSMO-SkyMed is a constellation of four X-band high-resolution radar satellites with a minimum revisit period of 12 hours.These satellites can obtain ascending and descending synthetic aperture radar(SAR)images with very similar periods for use in the three-dimensional(3D)inversion of glacier velocities.In this paper,based on ascending and descending COSMO-SkyMed data acquired at nearly the same time,the surface velocity of the Yiga Glacier,located in the Jiali County,Tibet,China,is estimated in four directions using an offset tracking technique during the periods of 16 January to 3 February 2017 and 1 February to 19 February 2017.Through the geometrical relationships between the measurements and the SAR images,the least square method is used to retrieve the 3D components of the glacier surface velocity in the eastward,northward and upward directions.The results show that applying the offset tracking technique to COSMO-SkyMed images can be used to derive the true 3D velocity of a glacier’s surface.During the two periods,the Yiga Glacier had a stable velocity,and the maximum surface velocity,2.4 m/d,was observed in the middle portion of the glacier,which corresponds to the location of the steepest slope.展开更多
In this paper,the crack process of the A74 iceberg is carefully monitored in different aspects by using synthetic aperture radar(SAR)images.First,a offset tracking strategy is designed to retrieve the temporal evoluti...In this paper,the crack process of the A74 iceberg is carefully monitored in different aspects by using synthetic aperture radar(SAR)images.First,a offset tracking strategy is designed to retrieve the temporal evolution of the glacier velocity field.Secondly,a signal coherence factor(SCF)is proposed to analyze the interferometric signals.The resulting SCF maps can present a more distinct rupture pattern than the SAR magnitude images,which enables the development of rift to be tracked more precisely.Thirdly,a new approach is proposed to explore the temporal change of the ice flow.Since this approach is based on interferometric phase signals,it is more sensitive than the offset tracking technique.Consequently,the abnormal variation signals associated with the rupture process can be discovered from the experimental results in an earlier stage.The results also show that the area with abnormal signals is almost identical to the region of the calved ice,which demonstrates that the scale of the iceberg might be predicted at least two months before the rupture event.Furthermore,such a consistent pattern may indicate a total alteration of ice characteristics,implying that the complete separation between A74 and BIS is inevitable.展开更多
The mining subsidence in the mining area is fast, large in magnitude and long in duration, which easily leads to serious incoherence of SAR interference and makes the conventional D-InSAR technology unable to obtain e...The mining subsidence in the mining area is fast, large in magnitude and long in duration, which easily leads to serious incoherence of SAR interference and makes the conventional D-InSAR technology unable to obtain effective measurement values. The Offset-Tracking method does not require phase unwrapping and does not require the coherence of SAR data, but its accuracy depends on the resolution of SAR images used, which is lower than that of D-InSAR. In this paper, a mining area surface subsidence field extraction method combining D-InSAR and Offset-Tracking technology is proposed. Through the effective fusion of D-InSAR and Offset-Tracking observation results, comprehensive, objective and accurate surface deformation can be obtained.展开更多
The surface velocity is one of the most important characteristics of glaciers.Monitoring and mapping glacier movements are of great significance for the studies of sea-level rise,glacier mass balance and dynamics,glob...The surface velocity is one of the most important characteristics of glaciers.Monitoring and mapping glacier movements are of great significance for the studies of sea-level rise,glacier mass balance and dynamics,global warming,and the management of freshwater resources.It is also essential for the early warnings of hazards caused by ice avalanches.SAR imaging geodesy has been developed for measuring glacier velocity,especially the pixel-offset tracking method.This paper introduces some basic concepts of glaciology and principles of various SAR imaging geodesy methods,with a detailed presentation about the developments in the applications of the pixel-offset tracking method.Finally,the challenges and future prospects of SAR imaging geodesy in glacier monitoring are discussed.展开更多
The 2016 MW7.8 Kaikoura earthquake struck the northern part of south Island,New Zealand,within the active and complex Australia-Pacific plate boundary system.Firstly,we used the InSAR method to obtain coseismic LOS de...The 2016 MW7.8 Kaikoura earthquake struck the northern part of south Island,New Zealand,within the active and complex Australia-Pacific plate boundary system.Firstly,we used the InSAR method to obtain coseismic LOS deformation fields based on SAR images and applied offset tracking methods to obtain offset measurements based on optical satellite images.The maximum displacement of about 6 m is detected in the direction away from the satellite on the south-west side and also towards the satellite on the north-east side.The 3D deformation field is then resolved by the combination of these measurements with a least-square solve method,and comparisons with 3 components of GPS stations show good consistency.Despite complex features demonstrated in the 3D deformation field,there are still clear spatial correlations between surface deformation and faults distribution.It reveals that more than ten faults were ruptured during the earthquake,including some faults were previously understudies for their tectonic activities.The maximum horizontal deformation of about 10 m occurs along the Kekerengu fault with the vertical deformation up to 2 m.The 3D deformation shows that the mainshock is a multisegments faulting with a rupture process of strike-slip,compression,transpressional rupture and strike-slip in space along the NE direction.展开更多
Landslides are destructive geohazards to people and infrastructure,resulting in hundreds of deaths and billions of dollars of damage every year.Therefore,mapping the rate of deformation of such geohazards and understa...Landslides are destructive geohazards to people and infrastructure,resulting in hundreds of deaths and billions of dollars of damage every year.Therefore,mapping the rate of deformation of such geohazards and understanding their mechanics is of paramount importance to mitigate the resulting impacts and properly manage the associated risks.In this paper,the main outcomes relevant to the joint European Space Agency(ESA)and the Chinese Ministry of Science and Technology(MOST)Dragon-5 initiative cooperation project ID 59,339“Earth observation for seismic hazard assessment and landslide early warning system”are reported.The primary goals of the project are to further develop advanced SAR/InSAR and optical techniques to investigate seismic hazards and risks,detect potential landslides in wide regions,and demonstrate EO-based landslide early warning system over selected landslides.This work only focuses on the landslide hazard content of the project,and thus,in order to achieve these objectives,the following tasks were developed up to now:a)a procedure for phase unwrapping errors and tropospheric delay correction;b)an improvement of a cross-platform SAR offset tracking method for the retrieval of long-term ground displacements;c)the application of polarimetric SAR interferometry(PolInSAR)to increase the number and quality of monitoring points in landslide-prone areas;d)the semiautomatic mapping and preliminary classification of active displacement areas on wide regions;e)the modeling and identification of landslides in order to identify triggering factors or predict future displacements;and f)the application of an InSAR-based landslide early warning system on a selected site.The achieved results,which mainly focus on specific sensitive regions,provide essential assets for planning present and future scientific activities devoted to identifying,mapping,characterizing,monitoring and predicting landslides,as well as for the implementation of early warning systems.展开更多
To achieve the track following and collision avoidance of underactuated unmanned surface vehicle(USV),autonomous navigation model based on model predictive control is established by including the track offset,speed va...To achieve the track following and collision avoidance of underactuated unmanned surface vehicle(USV),autonomous navigation model based on model predictive control is established by including the track offset,speed variation and rule compliance as the evaluation functions and including the ship domain of dynamic/static navigation obstacles and the mechanical characteristics limitation as constraints.The effectiveness of the model for autonomous navigation of USV in the situation of multi-ship encounters and in the complex waters with both dynamic and static obstructions is verified by several groups of simulation work.The simulation results show that the proposed model can realize the autonomous navigation of the underactuated USV under the complex waters.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 41874005 and 41929001)the Fundamental Research Funds for the Central Universities,CHD (Grant Nos. 300102269712 and 300102269303)+1 种基金by the China Geological Survey Projects (Grant Nos. DD20190637 and DD20190647)supported by a Chinese Scholarship Council studentship awarded to Xiaojie Liu (Grant No. 202006560031)。
文摘Multi-dimensional, long-term time series displacement monitoring is crucial for generating early warnings for active landslides and for mitigating geohazards. The synthetic aperture radar(SAR) interferometry method has been widely applied to achieve small-gradient landslide displacement monitoring;however, measuring the landslide displacement with a steep gradient has posed certain challenges. In comparison, the SAR offset tracking method is a powerful tool for mapping large-gradient landslide displacement in both the slant-range and azimuth directions. Nevertheless, there are some limitations in the existing SAR offset tracking approaches:(i) the measurement accuracy is greatly reduced by the extreme topography relief in high mountain areas,(ii) a fixed matching window from expert experience is usually adopted in the calculation of cross-correlation,(iii) estimating the long-term displacements between the SAR images from cross-platforms and with longer spatiotemporal baselines is a challenging task, and(iv) it is difficult to calculate the three-dimensional(3D) landslide displacements using a single SAR dataset.Additionally, only a few studies have focused on how to realize early warning of landslide deformation using SAR measurements.To address these issues, this paper presents an improved cross-platform SAR offset tracking method, which can not only estimate high-precision landslide displacements in two and three dimensions but also calculate long-term time series displacements over a decade using cross-platform SAR offset tracking measurements. Initially, we optimize the traditional SAR offset tracking workflow to estimate high-precision ground displacements, in which three improvements are highlighted:(i) an“ortho-rectification” operation is applied to restrain the effect of topography relief,(ii) an “adaptive matching window” is adopted in the cross-correlation computation, and(iii) a new strategy is proposed to combine all the possible offset pairs and optimally design the displacement inversion network based on the “optimization theory” of geodetic inversion. Next, robust mathematical equations are built to estimate the two-dimensional(2D) and 3D long-term time series landslide displacements using cross-platform SAR observations. The M-estimator is introduced into the 2D displacement inversion equation to restrain the outliers, and the total least squares criterion is adopted to estimate the 3D displacements considering the random errors in both the design matrix and observations. We take the Laojingbian landslide, Wudongde Reservoir Area(China), as an example to demonstrate the proposed method using ALOS/PALSAR-1 and ALOS/PALSAR-2 images. The results reveal that the proposed method significantly outperforms traditional methods. We also retrieve the movement direction of each pixel of the Laojingbian landslide using the proposed method, thus allowing us to understand the fine-scale landslide kinematics. Finally, we capture and analyze the acceleration characteristics of the landslide, perform an early warning of hazard, and forecast the future displacement evolution based on the 3D displacement time series coupled with the physical models of the rocks.
基金supported by the China Geological Survey under grant number[DD20160342]the China MOST-ESA Dragon Project-4 under grant number[32365]the National Science Foundation of China(NSFC)under grant number[41590852,41001264].
文摘COSMO-SkyMed is a constellation of four X-band high-resolution radar satellites with a minimum revisit period of 12 hours.These satellites can obtain ascending and descending synthetic aperture radar(SAR)images with very similar periods for use in the three-dimensional(3D)inversion of glacier velocities.In this paper,based on ascending and descending COSMO-SkyMed data acquired at nearly the same time,the surface velocity of the Yiga Glacier,located in the Jiali County,Tibet,China,is estimated in four directions using an offset tracking technique during the periods of 16 January to 3 February 2017 and 1 February to 19 February 2017.Through the geometrical relationships between the measurements and the SAR images,the least square method is used to retrieve the 3D components of the glacier surface velocity in the eastward,northward and upward directions.The results show that applying the offset tracking technique to COSMO-SkyMed images can be used to derive the true 3D velocity of a glacier’s surface.During the two periods,the Yiga Glacier had a stable velocity,and the maximum surface velocity,2.4 m/d,was observed in the middle portion of the glacier,which corresponds to the location of the steepest slope.
基金funded by Chongqing Basic Science And Frontier Technology Research Project[grant number 2017jcyjAX0229]China Postdoctoral Science Foundation[grant number 2019M660022XB].
文摘In this paper,the crack process of the A74 iceberg is carefully monitored in different aspects by using synthetic aperture radar(SAR)images.First,a offset tracking strategy is designed to retrieve the temporal evolution of the glacier velocity field.Secondly,a signal coherence factor(SCF)is proposed to analyze the interferometric signals.The resulting SCF maps can present a more distinct rupture pattern than the SAR magnitude images,which enables the development of rift to be tracked more precisely.Thirdly,a new approach is proposed to explore the temporal change of the ice flow.Since this approach is based on interferometric phase signals,it is more sensitive than the offset tracking technique.Consequently,the abnormal variation signals associated with the rupture process can be discovered from the experimental results in an earlier stage.The results also show that the area with abnormal signals is almost identical to the region of the calved ice,which demonstrates that the scale of the iceberg might be predicted at least two months before the rupture event.Furthermore,such a consistent pattern may indicate a total alteration of ice characteristics,implying that the complete separation between A74 and BIS is inevitable.
文摘The mining subsidence in the mining area is fast, large in magnitude and long in duration, which easily leads to serious incoherence of SAR interference and makes the conventional D-InSAR technology unable to obtain effective measurement values. The Offset-Tracking method does not require phase unwrapping and does not require the coherence of SAR data, but its accuracy depends on the resolution of SAR images used, which is lower than that of D-InSAR. In this paper, a mining area surface subsidence field extraction method combining D-InSAR and Offset-Tracking technology is proposed. Through the effective fusion of D-InSAR and Offset-Tracking observation results, comprehensive, objective and accurate surface deformation can be obtained.
文摘The surface velocity is one of the most important characteristics of glaciers.Monitoring and mapping glacier movements are of great significance for the studies of sea-level rise,glacier mass balance and dynamics,global warming,and the management of freshwater resources.It is also essential for the early warnings of hazards caused by ice avalanches.SAR imaging geodesy has been developed for measuring glacier velocity,especially the pixel-offset tracking method.This paper introduces some basic concepts of glaciology and principles of various SAR imaging geodesy methods,with a detailed presentation about the developments in the applications of the pixel-offset tracking method.Finally,the challenges and future prospects of SAR imaging geodesy in glacier monitoring are discussed.
基金co-supported by the National Key Research and Development Program of China(Grant No.2019YFC1509204)the National Nonprofit Fundamental Research Grant of China,Institute of Geology,China Earthquake Administration(Grant No.IGCEA2005 and No.IGCEA2014)the National Science Foundation of China(Grant No.41631073)
文摘The 2016 MW7.8 Kaikoura earthquake struck the northern part of south Island,New Zealand,within the active and complex Australia-Pacific plate boundary system.Firstly,we used the InSAR method to obtain coseismic LOS deformation fields based on SAR images and applied offset tracking methods to obtain offset measurements based on optical satellite images.The maximum displacement of about 6 m is detected in the direction away from the satellite on the south-west side and also towards the satellite on the north-east side.The 3D deformation field is then resolved by the combination of these measurements with a least-square solve method,and comparisons with 3 components of GPS stations show good consistency.Despite complex features demonstrated in the 3D deformation field,there are still clear spatial correlations between surface deformation and faults distribution.It reveals that more than ten faults were ruptured during the earthquake,including some faults were previously understudies for their tectonic activities.The maximum horizontal deformation of about 10 m occurs along the Kekerengu fault with the vertical deformation up to 2 m.The 3D deformation shows that the mainshock is a multisegments faulting with a rupture process of strike-slip,compression,transpressional rupture and strike-slip in space along the NE direction.
基金supported by the ESA-MOST China DRAGON-5 project with ref.59339,by the Spanish Ministry of Science and Innovation,the State Agency of Research(AEI)the European Funds for Regional Development under grant[grant number PID2020-117303GB-C22]+5 种基金by the Conselleria de Innovación,Universidades,Ciencia y Sociedad Digital in the framework of the project CIAICO/2021/335by the Natural Science Foundation of China[grant numbers 41874005 and 41929001]the Fundamental Research Funds for the Central University[grant numbers 300102269712 and 300102269303]China Geological Survey Project[grant numbers DD20190637 and DD20190647]Xiaojie Liu and Liuru Hu have been funded by Chinese Scholarship Council Grants Ref.[grant number 202006560031][grant number 202004180062],respectively.
文摘Landslides are destructive geohazards to people and infrastructure,resulting in hundreds of deaths and billions of dollars of damage every year.Therefore,mapping the rate of deformation of such geohazards and understanding their mechanics is of paramount importance to mitigate the resulting impacts and properly manage the associated risks.In this paper,the main outcomes relevant to the joint European Space Agency(ESA)and the Chinese Ministry of Science and Technology(MOST)Dragon-5 initiative cooperation project ID 59,339“Earth observation for seismic hazard assessment and landslide early warning system”are reported.The primary goals of the project are to further develop advanced SAR/InSAR and optical techniques to investigate seismic hazards and risks,detect potential landslides in wide regions,and demonstrate EO-based landslide early warning system over selected landslides.This work only focuses on the landslide hazard content of the project,and thus,in order to achieve these objectives,the following tasks were developed up to now:a)a procedure for phase unwrapping errors and tropospheric delay correction;b)an improvement of a cross-platform SAR offset tracking method for the retrieval of long-term ground displacements;c)the application of polarimetric SAR interferometry(PolInSAR)to increase the number and quality of monitoring points in landslide-prone areas;d)the semiautomatic mapping and preliminary classification of active displacement areas on wide regions;e)the modeling and identification of landslides in order to identify triggering factors or predict future displacements;and f)the application of an InSAR-based landslide early warning system on a selected site.The achieved results,which mainly focus on specific sensitive regions,provide essential assets for planning present and future scientific activities devoted to identifying,mapping,characterizing,monitoring and predicting landslides,as well as for the implementation of early warning systems.
基金the National Natural Science Foundation of China(No.51879119)the Key Projects of National Key Research and Development Program(No.2021YFB390150)+1 种基金the Natural Science Project of Fujian Province(Nos.2022J01323,2021J01822 and 2020J01660)the Fuzhou-Xiamen-Quanzhou Independent Innovation Region Cooperated Special Foundation(No.3502ZCQXT2021007)。
文摘To achieve the track following and collision avoidance of underactuated unmanned surface vehicle(USV),autonomous navigation model based on model predictive control is established by including the track offset,speed variation and rule compliance as the evaluation functions and including the ship domain of dynamic/static navigation obstacles and the mechanical characteristics limitation as constraints.The effectiveness of the model for autonomous navigation of USV in the situation of multi-ship encounters and in the complex waters with both dynamic and static obstructions is verified by several groups of simulation work.The simulation results show that the proposed model can realize the autonomous navigation of the underactuated USV under the complex waters.
