Position, velocity, and timing（PVT） signals from the Global Positioning System（GPS）are used throughout the world but the availability and reliability of these signals in all environments has become a subject of co...Position, velocity, and timing（PVT） signals from the Global Positioning System（GPS）are used throughout the world but the availability and reliability of these signals in all environments has become a subject of concern for both civilian and military applications. This presentation summarizes recent advances in navigation sensor technology, including GPS, inertial, and other navigation aids that address these concerns. Also addressed are developments in sensor integration technology with several examples described, including the Bluefin-21 system mechanization.展开更多
Integrating Global Navigation Satellite Systems(GNSS)in Simultaneous Localization and Mapping(SLAM)systems draws increasing attention to a global and continuous localization solution.Nonetheless,in dense urban environ...Integrating Global Navigation Satellite Systems(GNSS)in Simultaneous Localization and Mapping(SLAM)systems draws increasing attention to a global and continuous localization solution.Nonetheless,in dense urban environments,GNSS-based SLAM systems will suffer from the Non-Line-Of-Sight(NLOS)measurements,which might lead to a sharp deterioration in localization results.In this paper,we propose to detect the sky area from the up-looking camera to improve GNSS measurement reliability for more accurate position estimation.We present Sky-GVINS:a sky-aware GNSS-Visual-Inertial system based on a recent work called GVINS.Specifically,we adopt a global threshold method to segment the sky regions and non-sky regions in the fish-eye sky-pointing image and then project satellites to the image using the geometric relationship between satellites and the camera.After that,we reject satellites in non-sky regions to eliminate NLOS signals.We investigated various segmentation algorithms for sky detection and found that the Otsu algorithm reported the highest classification rate and computational efficiency,despite the algorithm's simplicity and ease of implementation.To evaluate the effectiveness of Sky-GVINS,we built a ground robot and conducted extensive real-world experiments on campus.Experimental results show that our method improves localization accuracy in both open areas and dense urban environments compared to the baseline method.Finally,we also conduct a detailed analysis and point out possible further directions for future research.For detailed information,visit our project website at https://github.com/SJTU-ViSYS/Sky-GVINS.展开更多
Global Navigation Satellite Systems(GNSSs)face significant security threats from spoofing attacks.Typical anti-spoofing methods rely on estimating the delays between spoofing and authentic signals using multicorrelato...Global Navigation Satellite Systems(GNSSs)face significant security threats from spoofing attacks.Typical anti-spoofing methods rely on estimating the delays between spoofing and authentic signals using multicorrelator outputs.However,the accuracy of the delay estimation is limited by the spacing of the correlators.To address this,an innovative anti-spoofing method is introduced,which incorporates distinct coarse and refined stages for more accurate spoofing estimation.By leveraging the coarse delay estimates obtained through maximum likelihood estimation,the proposed method establishes the Windowed Sum of the Relative Delay(WSRD)statistics to detect the presence of spoofing signals.The iterative strategy is then employed to enhance the precision of the delay estimation.To further adapt to variations in the observation noise caused by spoofing intrusions and restore precise position,velocity,and timing solutions,an adaptive extended Kalman filter is proposed.This comprehensive framework offers detection,mitigation,and recovery against spoofing attacks.Experimental validation using datasets from the Texas Spoofing Test Battery(TEXBAT)demonstrates the effectiveness of the proposed anti-spoofing method.With 41 correlators,the method achieves a detection rate exceeding 90%at a false alarm rate of 10-5,with position or time errors below 15 m.Notably,this refined anti-spoofing approach shows robust detection and mitigation capabilities,requiring only a single antenna without the need for additional external sensors.These advancements can significantly contribute to the development of GNSS anti-spoofing measures.展开更多
An M6.2 earthquake struck Jishishan County,Gansu,on December 18,2023,with its epicenter located in the arc-shaped tectonic belt formed by the Lajishan-Jishishan Fault.Continuous high-rate global navigational satellite...An M6.2 earthquake struck Jishishan County,Gansu,on December 18,2023,with its epicenter located in the arc-shaped tectonic belt formed by the Lajishan-Jishishan Fault.Continuous high-rate global navigational satellite system(GNSS)data were utilized to simulate real-time data resolution,enabling the rapid determination of coseismic static and dynamic deformation caused by the earthquake and the estimation of empirical magnitude.Far-field body waves served as constraints for the source rupture process,facilitating the analysis of potential seismogenic fault structures.GNSS stations within 30 km of the epicenter exhibited significant coseismic responses:horizontal peak displacement and velocity reached approximately 6.3 cm and 6.1 cm/s,respectively.Additionally,quasi-real-time differential positioning and post-event precise point positioning results were consistent throughout the source process.Vertical velocity,calculated via epoch-by-epoch differential velocity determination,showed clear coseismic signals,with peak values increasing to 2.6 cm/s.The empirical magnitude,based on displacement,was 5.99,while the magnitude derived from the velocity waveform amplitude was 6.05,both consistent with the moment magnitude.The dynamic displacement distribution preliminarily suggests directional effects of northward rupture propagation,aligning with subsequent aftershock occurrences.Finite fault inversion results,based on the two nodal planes of the focal mechanism,indicate that asperity ruptures concentrated at the hypocenter played a major role.These ruptures propagated from the hypocenter to shallow regions and northward,lasting approximately 10 s.Although the coseismic deformation determined by sparse high-rate GNSS cannot constrain the specific fault dip angle,the relationship between rupture propagation direction from the seismic source model and aftershock distribution suggests a northeast-dipping fault.Moreover,seismic source models representing single faults as geometric structures can only simulate permanent formations.In contrast,the conjugate fault model,which aligns with aftershock distributions,more accurately explains high-rate GNSS displacement waveforms.Considering both regional tectonics and geological survey results,the seismogenic fault is believed to be a local northeast-dipping blind thrust fault.Northward rupture propagation may have caused the movement of conjugate faults.This study is an effective case of using high-rate GNSS for rapid earthquake response,providing a reference basis for understanding the seismic activity patterns and earthquake disaster prevention in the region.展开更多
With the widespread application of global navigation satellite system(GNSS),spoofing attacks pose a threat to the security and reliability of GNSS.It is of great significance to design effective GNSS spoofing detectio...With the widespread application of global navigation satellite system(GNSS),spoofing attacks pose a threat to the security and reliability of GNSS.It is of great significance to design effective GNSS spoofing detection technology to ensure the security and reliability of GNSS system applications for receiver users.Traditional spoofing detection techniques generally only determine whether a spoofing attack has occurred by monitoring the feature changes of one or two data information in the receiver.However,some spoofing modes can cleverly make the monitored data very close to the real data,thus avoiding these detection methods and easily making them ineffective.In this study,a GNSS spoofing jamming detection method based on hybrid kernel relevance vector machine(RVM)is proposed.The improved signal quality monitoring(SQM)movement variance,carrier noise ratio movement variance,pseudo range Doppler consistency,pseudorange residual,Doppler frequency,clock offset and clock drift are used as detection characteristics.This technology can detect GNSS spoofing signals,effectively improving the safety and reliability of GNSS systems.The experimental results show that this technology has high detection accuracy and anti-interference ability and can effectively respond to various forms of spoofing attacks.展开更多
The Global Navigation Satellite System(GNSS)has been widely adopted in numerous fields,including intelligent transportation,remote sensing,and aeronautical and astronautical engineering.As new navigation approaches,te...The Global Navigation Satellite System(GNSS)has been widely adopted in numerous fields,including intelligent transportation,remote sensing,and aeronautical and astronautical engineering.As new navigation approaches,technologies,and applications continue to emerge,they attract significant global attention.Ensuring reliable positioning solutions with high accuracy,strong anti-interference capabilities,high availability and low integrity risks has become increasingly critical.展开更多
Understanding the viscoelastic structure of subduction zones is essential for assessing seismic hazards and understanding subduction-zone dynamics.However,the influence of lateral variations in elastic upper-plate thi...Understanding the viscoelastic structure of subduction zones is essential for assessing seismic hazards and understanding subduction-zone dynamics.However,the influence of lateral variations in elastic upper-plate thickness(H_(c))remains poorly constrained and is often overlooked.In this study,we use two-dimensional forward viscoelastic earthquake-cycle models to fit both horizontal and vertical Global Navigation Satellite System(GNSS)observations.We identify a clear trade-off between locking depth(D)and H_(c)in both components.To resolve this ambiguity,we incorporate constraints from thermal models and tremor distributions along the Cascadia Subduction Zone.As a novel result extending beyond previous kinematic models,our results reveal a systematic northward increase in H_(c)from~20 km to~30 km.This trend correlates with increasing oceanic plate age and likely reflects variations in the subaccretion and wedge-cooling processes along the trench-parallel direction.In contrast,D remains relatively uniform at~10 km,consistent with previous findings.These results demonstrate the robustness of our approach for simultaneously constraining H_(c)and D,and they suggest it may be applied to other subduction zones.Lateral variations in H_(c)significantly affect crust deformation and should not be ignored in earthquake-cycle models.Accounting for these heterogeneities improves estimates of H_(c)and D and enhances our understanding of megathrust locking,seismic hazard potential,and the physical conditions controlling episodic tremor and slip events.展开更多
In order to solve the problem that the global navigation satellite system（GNSS） receivers can hardly detect the GNSS spoofing when they are deceived by a spoofer,a model-based approach for the identification of the ...In order to solve the problem that the global navigation satellite system（GNSS） receivers can hardly detect the GNSS spoofing when they are deceived by a spoofer,a model-based approach for the identification of the GNSS spoofing is proposed.First,a Hammerstein model is applied to model the spoofer/GNSS transmitter and the wireless channel.Then,a novel method based on the uncultivated wolf pack algorithm（UWPA） is proposed to estimate the model parameters.Taking the estimated model parameters as a feature vector,the identification of the spoofing is realized by comparing the Euclidean distance between the feature vectors.Simulations verify the effectiveness and the robustness of the proposed method.The results show that,compared with the other identification algorithms,such as least square（LS）,the iterative method and the bat-inspired algorithm（BA）,although the UWPA has a little more time-eomplexity than the LS and the BA algorithm,it has better estimation precision of the model parameters and higher identification rate of the GNSS spoofing,even for relative low signal-to-noise ratios.展开更多
Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely main...Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely maintain a fairly close distance between UAVs and to achieve inner-system collision avoidance.However,Global Navigation Satellite System(GNSS)measurements are vulnerable to erroneous signals in urban canyons,which could potentially lead to catastrophic consequences.Accordingly,on the basis of performing relative positioning with double differenced pseudoranges,this paper develops an integrity monitoring framework to improve navigation integrity(a measure of reliability)in urban environments.On the one hand,this framework includes a fault detection and exclusion scheme to protect against measurement faults.To accommodate urban scenarios,spatial dependence in the faults are taken into consideration by this scheme.On the other hand,relative protection level is rigorously derived to describe the probabilistic error bound of the navigation output.This indicator can be used to evaluate collision risk and to warn collision danger in real time.The proposed algorithms are validated by both simulations and flight experiments.Simulation results quantitatively reveal the sensitivity of navigation performance to receiver configurations and environmental conditions.And experimental results suggest high efficiency and effectiveness of the new integrity monitoring framework.展开更多
As high-dynamics and weak-signal are of two primary concerns of navigation using Global Navigation Satellite System(GNSS)signals,an acquisition algorithm based on threetime fractional Fourier transform(FRFT)is present...As high-dynamics and weak-signal are of two primary concerns of navigation using Global Navigation Satellite System(GNSS)signals,an acquisition algorithm based on threetime fractional Fourier transform(FRFT)is presented to simplify the calculation effectively.Firstly,the correlation results similar to linear frequency modulated(LFM)signals are derived on the basis of the high dynamic GNSS signal model.Then,the principle of obtaining the optimum rotation angle is analyzed,which is measured by FRFT projection lengths with two selected rotation angles.Finally,Doppler shift,Doppler rate,and code phase are accurately estimated in a real-time and low signal to noise ratio(SNR)wireless communication system.The theoretical analysis and simulation results show that the fast FRFT algorithm can accurately estimate the high dynamic parameters by converting the traditional two-dimensional search process to only three times FRFT.While the acquisition performance is basically the same,the computational complexity and running time are greatly reduced,which is more conductive to practical application.展开更多
High dynamic conditions impose critical challenges on Global Navigation Satellite System(GNSS)receivers,leading to large tracking errors or even loss of tracking.Current methods that intend to improve receivers’adapt...High dynamic conditions impose critical challenges on Global Navigation Satellite System(GNSS)receivers,leading to large tracking errors or even loss of tracking.Current methods that intend to improve receivers’adaptability for high dynamics require either complicated structures or prior statistical information of noises.This paper proposes a high dynamics algorithm based on steepest ascent method that can circumvent the deficiencies of existing methods.First,the relationship between the error of carrier tracking and the maximum of Fast Fourier Transform(FFT)outputs is established,and a performance function based on the steepest ascent method is designed.It can keep stable in high dynamics.Second,a new carrier-tracking loop is constructed by deploying the performance function.When the variation of GPS receiver acceleration ranges from 10 g to 100 g,compared with the PLL that either loses lock or keeps tracking accuracy less than 33.89 Hz,the experimental results show that the proposed method can not only keep tracking,but also achieve tracking accuracy more than 2.77 Hz.展开更多
The full constellation of Chinese Global Navigation Satellite System(GNSS)Bei Dou-3 has been deployed completely and started fully operational service.In addition to providing global Positioning,Navigation and Timing(...The full constellation of Chinese Global Navigation Satellite System(GNSS)Bei Dou-3 has been deployed completely and started fully operational service.In addition to providing global Positioning,Navigation and Timing(PNT)services,the Bei Dou-3 satellites transmissions can also be used as the sources of illumination for Earth Observation(EO)with a bistatic radar configuration.This innovative EO concept,known as GNSS reflectometry(GNSS-R),allows to measure the Earth surface characteristics at high resolution via the reflected L-band radar signals collected by a constellation of small,low cost and low Earth orbiting satellites.For the first time in orbit,earth reflected Bei Dou-3 signal has been detected from the limited sets of raw data collected by the NASA’s Cyclone GNSS(CYGNSS)constellation.The feasibility of spaceborne Bei Dou-3 reflections on two typical applications,including sea surface wind and flooding inundation detection,has been demonstrated.The methodology and results give new strength to the prospect of new spaceborne GNSS-R instruments and missions,which can make multi-GNSS reflectometry observations available to better capture rapidly changing weather systems at better spatio-temporal scales.展开更多
Once the spoofer has controlled the navigation sys-tem of unmanned aerial vehicle(UAV),it is hard to effectively control the error convergence to meet the threshold condition only by adjusting parameters of estimation...Once the spoofer has controlled the navigation sys-tem of unmanned aerial vehicle(UAV),it is hard to effectively control the error convergence to meet the threshold condition only by adjusting parameters of estimation if estimation of the spoofer on UAV has continuous observation error.Aiming at this problem,the influence of the spoofer’s state estimation error on spoofing effect and error convergence conditions is theoretically analyzed,and an improved adaptively robust estimation algo-rithm suitable for steady-state linear quadratic estimator is pro-posed.It enables the spoofer’s estimator to reliably estimate UAV status in real time,improves the robustness of the estima-tor in responding to observation errors,and accelerates the con-vergence time of error control.Simulation experiments show that the mean value of normalized innovation squared(NIS)is reduced by 88.5%,and the convergence time of NIS value is reduced by 76.3%,the convergence time of true trajectory error of UAV is reduced by 42.3%,the convergence time of estimated trajectory error of UAV is reduced by 67.4%,the convergence time of estimated trajectory error of the spoofer is reduced by 33.7%,and the convergence time of broadcast trajectory error of the spoofer is reduced by 54.8%when the improved algorithm is used.The improved algorithm can make UAV deviate from pre-set trajectory to spoofing trajectory more effectively and more subtly.展开更多
The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centi...The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.展开更多
A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively....A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively.In this method,the GNSS signal is first decomposed into several intrinsic mode functions(IMFs)and a residual through EEMD.Then,the IMFs and residual are classified into noise terms,mixed terms,and useful terms according to a combined classification criterion.Finally,the mixed term denoised by wavelet and the useful term are reconstructed to obtain the multipath error and thus enable an error correction model to be built.The measurement data provided by the Curtin GNSS Research Center were used for processing and analysis.Results show that the proposed method can separate multipath error from GNSS data to a great extent,thereby effectively addressing the defects of EEMD and wavelet methods on multipath error weakening.The error correction model established with the separated multipath error has a higher accuracy and provides a certain reference value for research on related signal processing.展开更多
Global Positioning System(GPS)services could be improved through prediction of ionospheric delays for satellite-based radio signals.With respect to latitude,longitude,local time,season,solar cycle and geomagnetic acti...Global Positioning System(GPS)services could be improved through prediction of ionospheric delays for satellite-based radio signals.With respect to latitude,longitude,local time,season,solar cycle and geomagnetic activity the Total Electron Content(TEC)have significant variations in both time and space.These temporal and spatial TEC variations driven by interplanetary space weather conditions such as solar and geomagnetic activities can degrade the communication and navigation links of GPS.Hence,in this paper,performance of TEC forecasting models based on Neural Networks(NN)have been evaluated to forecast(1-h ahead)ionospheric TEC over equatorial low latitude Bengaluru e12:97+N;77:59+ET,Global Navigation Satellite System(GNSS)station,India.The VTEC data is collected for 2009 e2016(8 years)during current 24 th solar cycle.The input space for the NN models comprise the solar Extreme UV flux,F10.7 proxy,a geomagnetic planetary A index(AP)index,sunspot number(SSN),disturbance storm time(DST)index,solar wind speed(Vsw),solar wind proton density(Np),Interplanetary Magnetic Field(IMF Bz).The performance of NN based TEC forecast models and International Reference Ionosphere,IRI-2016 global TEC model has evaluated during testing period,2016.The NN based model driven by all the inputs,which is a NN unified model(NNunq)has shown better accuracy with Mean Absolute Error(MAE)of 3.15 TECU,Mean Square Deviation(MSD)of 16.8 and Mean Absolute Percentage Error(MAPE)of 19.8%and is 1 e25%more accurate than the other NN based TEC forecast models(NN1,NN2 and NN3)and IRI-2016 model.NNunq model has less Root Mean Square Error(RMSE)value 3.8 TECU and highest goodness-of-fit(R2)with 0.85.The experimental results imply that NNunq/NN1 model forecasts ionospheric TEC accurately across equatorial low-latitude GNSS station and IRI-2016 model performance is necessarily improved as its forecast accuracy is limited to 69 e70%.展开更多
文摘Position, velocity, and timing（PVT） signals from the Global Positioning System（GPS）are used throughout the world but the availability and reliability of these signals in all environments has become a subject of concern for both civilian and military applications. This presentation summarizes recent advances in navigation sensor technology, including GPS, inertial, and other navigation aids that address these concerns. Also addressed are developments in sensor integration technology with several examples described, including the Bluefin-21 system mechanization.
基金supported by National Key R&D Plan of China[2022YFB3903800]and NSFC[62073214].
文摘Integrating Global Navigation Satellite Systems(GNSS)in Simultaneous Localization and Mapping(SLAM)systems draws increasing attention to a global and continuous localization solution.Nonetheless,in dense urban environments,GNSS-based SLAM systems will suffer from the Non-Line-Of-Sight(NLOS)measurements,which might lead to a sharp deterioration in localization results.In this paper,we propose to detect the sky area from the up-looking camera to improve GNSS measurement reliability for more accurate position estimation.We present Sky-GVINS:a sky-aware GNSS-Visual-Inertial system based on a recent work called GVINS.Specifically,we adopt a global threshold method to segment the sky regions and non-sky regions in the fish-eye sky-pointing image and then project satellites to the image using the geometric relationship between satellites and the camera.After that,we reject satellites in non-sky regions to eliminate NLOS signals.We investigated various segmentation algorithms for sky detection and found that the Otsu algorithm reported the highest classification rate and computational efficiency,despite the algorithm's simplicity and ease of implementation.To evaluate the effectiveness of Sky-GVINS,we built a ground robot and conducted extensive real-world experiments on campus.Experimental results show that our method improves localization accuracy in both open areas and dense urban environments compared to the baseline method.Finally,we also conduct a detailed analysis and point out possible further directions for future research.For detailed information,visit our project website at https://github.com/SJTU-ViSYS/Sky-GVINS.
基金co-supported by the Tianjin Research innovation Project for Postgraduate Students,China(No.2022BKYZ039)the China Postdoctoral Science Foundation(No.2023M731788)the National Natural Science Foundation of China(No.62303246)。
文摘Global Navigation Satellite Systems(GNSSs)face significant security threats from spoofing attacks.Typical anti-spoofing methods rely on estimating the delays between spoofing and authentic signals using multicorrelator outputs.However,the accuracy of the delay estimation is limited by the spacing of the correlators.To address this,an innovative anti-spoofing method is introduced,which incorporates distinct coarse and refined stages for more accurate spoofing estimation.By leveraging the coarse delay estimates obtained through maximum likelihood estimation,the proposed method establishes the Windowed Sum of the Relative Delay(WSRD)statistics to detect the presence of spoofing signals.The iterative strategy is then employed to enhance the precision of the delay estimation.To further adapt to variations in the observation noise caused by spoofing intrusions and restore precise position,velocity,and timing solutions,an adaptive extended Kalman filter is proposed.This comprehensive framework offers detection,mitigation,and recovery against spoofing attacks.Experimental validation using datasets from the Texas Spoofing Test Battery(TEXBAT)demonstrates the effectiveness of the proposed anti-spoofing method.With 41 correlators,the method achieves a detection rate exceeding 90%at a false alarm rate of 10-5,with position or time errors below 15 m.Notably,this refined anti-spoofing approach shows robust detection and mitigation capabilities,requiring only a single antenna without the need for additional external sensors.These advancements can significantly contribute to the development of GNSS anti-spoofing measures.
基金funded by the Science for earthquake Resilience(No.XH24014YC)the Sixth Phase“169 Project”Scientific Research Project of Zhenjiang City(No.25)+1 种基金the Scientific Research Fund from Institute of Seismology,CEA and National Institute of Natural Hazards,Ministry of Emergency Management of China(No.IS202216316)the Open Research Fund of the National Field Observation and Research Station for Gravity and Solid Tides,Wuhan(Nos.WHYMZ202113 and WHYWZ202301)。
文摘An M6.2 earthquake struck Jishishan County,Gansu,on December 18,2023,with its epicenter located in the arc-shaped tectonic belt formed by the Lajishan-Jishishan Fault.Continuous high-rate global navigational satellite system(GNSS)data were utilized to simulate real-time data resolution,enabling the rapid determination of coseismic static and dynamic deformation caused by the earthquake and the estimation of empirical magnitude.Far-field body waves served as constraints for the source rupture process,facilitating the analysis of potential seismogenic fault structures.GNSS stations within 30 km of the epicenter exhibited significant coseismic responses:horizontal peak displacement and velocity reached approximately 6.3 cm and 6.1 cm/s,respectively.Additionally,quasi-real-time differential positioning and post-event precise point positioning results were consistent throughout the source process.Vertical velocity,calculated via epoch-by-epoch differential velocity determination,showed clear coseismic signals,with peak values increasing to 2.6 cm/s.The empirical magnitude,based on displacement,was 5.99,while the magnitude derived from the velocity waveform amplitude was 6.05,both consistent with the moment magnitude.The dynamic displacement distribution preliminarily suggests directional effects of northward rupture propagation,aligning with subsequent aftershock occurrences.Finite fault inversion results,based on the two nodal planes of the focal mechanism,indicate that asperity ruptures concentrated at the hypocenter played a major role.These ruptures propagated from the hypocenter to shallow regions and northward,lasting approximately 10 s.Although the coseismic deformation determined by sparse high-rate GNSS cannot constrain the specific fault dip angle,the relationship between rupture propagation direction from the seismic source model and aftershock distribution suggests a northeast-dipping fault.Moreover,seismic source models representing single faults as geometric structures can only simulate permanent formations.In contrast,the conjugate fault model,which aligns with aftershock distributions,more accurately explains high-rate GNSS displacement waveforms.Considering both regional tectonics and geological survey results,the seismogenic fault is believed to be a local northeast-dipping blind thrust fault.Northward rupture propagation may have caused the movement of conjugate faults.This study is an effective case of using high-rate GNSS for rapid earthquake response,providing a reference basis for understanding the seismic activity patterns and earthquake disaster prevention in the region.
基金supported in part by the Key Science and Technology Research of Henan Province(252102210239,242102211029,242102211105)the Henan Provincial Key Laboratory of Smart Lighting Open Fund(2023KF06)+2 种基金Zhumadian Science and Technology Youth Innovation Special Fund(QNZX202407)the Computer Basic Education Teaching Research Project of the National Research Society for Computer Basic Education in Higher Education Institutions(2024-AFCEC-393)the Young Backbone Teacher Support Program of Huanghuai University.
文摘With the widespread application of global navigation satellite system(GNSS),spoofing attacks pose a threat to the security and reliability of GNSS.It is of great significance to design effective GNSS spoofing detection technology to ensure the security and reliability of GNSS system applications for receiver users.Traditional spoofing detection techniques generally only determine whether a spoofing attack has occurred by monitoring the feature changes of one or two data information in the receiver.However,some spoofing modes can cleverly make the monitored data very close to the real data,thus avoiding these detection methods and easily making them ineffective.In this study,a GNSS spoofing jamming detection method based on hybrid kernel relevance vector machine(RVM)is proposed.The improved signal quality monitoring(SQM)movement variance,carrier noise ratio movement variance,pseudo range Doppler consistency,pseudorange residual,Doppler frequency,clock offset and clock drift are used as detection characteristics.This technology can detect GNSS spoofing signals,effectively improving the safety and reliability of GNSS systems.The experimental results show that this technology has high detection accuracy and anti-interference ability and can effectively respond to various forms of spoofing attacks.
文摘The Global Navigation Satellite System(GNSS)has been widely adopted in numerous fields,including intelligent transportation,remote sensing,and aeronautical and astronautical engineering.As new navigation approaches,technologies,and applications continue to emerge,they attract significant global attention.Ensuring reliable positioning solutions with high accuracy,strong anti-interference capabilities,high availability and low integrity risks has become increasingly critical.
基金supported by the National Key R&D Program of China(Grant No.2023YFF0803200)the National Natural Science Foundation of China(Grant No.42288201).
文摘Understanding the viscoelastic structure of subduction zones is essential for assessing seismic hazards and understanding subduction-zone dynamics.However,the influence of lateral variations in elastic upper-plate thickness(H_(c))remains poorly constrained and is often overlooked.In this study,we use two-dimensional forward viscoelastic earthquake-cycle models to fit both horizontal and vertical Global Navigation Satellite System(GNSS)observations.We identify a clear trade-off between locking depth(D)and H_(c)in both components.To resolve this ambiguity,we incorporate constraints from thermal models and tremor distributions along the Cascadia Subduction Zone.As a novel result extending beyond previous kinematic models,our results reveal a systematic northward increase in H_(c)from~20 km to~30 km.This trend correlates with increasing oceanic plate age and likely reflects variations in the subaccretion and wedge-cooling processes along the trench-parallel direction.In contrast,D remains relatively uniform at~10 km,consistent with previous findings.These results demonstrate the robustness of our approach for simultaneously constraining H_(c)and D,and they suggest it may be applied to other subduction zones.Lateral variations in H_(c)significantly affect crust deformation and should not be ignored in earthquake-cycle models.Accounting for these heterogeneities improves estimates of H_(c)and D and enhances our understanding of megathrust locking,seismic hazard potential,and the physical conditions controlling episodic tremor and slip events.
基金The National Natural Science Foundation of China(No.61271214,61471152)the Postdoctoral Science Foundation of Jiangsu Province(No.1402023C)the Natural Science Foundation of Zhejiang Province(No.LZ14F010003)
文摘In order to solve the problem that the global navigation satellite system（GNSS） receivers can hardly detect the GNSS spoofing when they are deceived by a spoofer,a model-based approach for the identification of the GNSS spoofing is proposed.First,a Hammerstein model is applied to model the spoofer/GNSS transmitter and the wireless channel.Then,a novel method based on the uncultivated wolf pack algorithm（UWPA） is proposed to estimate the model parameters.Taking the estimated model parameters as a feature vector,the identification of the spoofing is realized by comparing the Euclidean distance between the feature vectors.Simulations verify the effectiveness and the robustness of the proposed method.The results show that,compared with the other identification algorithms,such as least square（LS）,the iterative method and the bat-inspired algorithm（BA）,although the UWPA has a little more time-eomplexity than the LS and the BA algorithm,it has better estimation precision of the model parameters and higher identification rate of the GNSS spoofing,even for relative low signal-to-noise ratios.
基金This study was co-supported by SJTU Global Strategic Partnership Fund(2019 SJTU–UoT)Master Research Agreement between SJTU and Honeywell Technology Solutions China(HTSC).
文摘Formation flight of multiple Unmanned Aerial Vehicles(UAVs)is expected to bring significant benefits to a wide range of applications.Accurate and reliable relative position information is a prerequisite to safely maintain a fairly close distance between UAVs and to achieve inner-system collision avoidance.However,Global Navigation Satellite System(GNSS)measurements are vulnerable to erroneous signals in urban canyons,which could potentially lead to catastrophic consequences.Accordingly,on the basis of performing relative positioning with double differenced pseudoranges,this paper develops an integrity monitoring framework to improve navigation integrity(a measure of reliability)in urban environments.On the one hand,this framework includes a fault detection and exclusion scheme to protect against measurement faults.To accommodate urban scenarios,spatial dependence in the faults are taken into consideration by this scheme.On the other hand,relative protection level is rigorously derived to describe the probabilistic error bound of the navigation output.This indicator can be used to evaluate collision risk and to warn collision danger in real time.The proposed algorithms are validated by both simulations and flight experiments.Simulation results quantitatively reveal the sensitivity of navigation performance to receiver configurations and environmental conditions.And experimental results suggest high efficiency and effectiveness of the new integrity monitoring framework.
基金supported by Shenzhen Science and Technology Program(JCYJ20180508152046428).
文摘As high-dynamics and weak-signal are of two primary concerns of navigation using Global Navigation Satellite System(GNSS)signals,an acquisition algorithm based on threetime fractional Fourier transform(FRFT)is presented to simplify the calculation effectively.Firstly,the correlation results similar to linear frequency modulated(LFM)signals are derived on the basis of the high dynamic GNSS signal model.Then,the principle of obtaining the optimum rotation angle is analyzed,which is measured by FRFT projection lengths with two selected rotation angles.Finally,Doppler shift,Doppler rate,and code phase are accurately estimated in a real-time and low signal to noise ratio(SNR)wireless communication system.The theoretical analysis and simulation results show that the fast FRFT algorithm can accurately estimate the high dynamic parameters by converting the traditional two-dimensional search process to only three times FRFT.While the acquisition performance is basically the same,the computational complexity and running time are greatly reduced,which is more conductive to practical application.
基金funded by National Natural Science Foundation of China(Nos.61533008,61603181,61673208,61873125)。
文摘High dynamic conditions impose critical challenges on Global Navigation Satellite System(GNSS)receivers,leading to large tracking errors or even loss of tracking.Current methods that intend to improve receivers’adaptability for high dynamics require either complicated structures or prior statistical information of noises.This paper proposes a high dynamics algorithm based on steepest ascent method that can circumvent the deficiencies of existing methods.First,the relationship between the error of carrier tracking and the maximum of Fast Fourier Transform(FFT)outputs is established,and a performance function based on the steepest ascent method is designed.It can keep stable in high dynamics.Second,a new carrier-tracking loop is constructed by deploying the performance function.When the variation of GPS receiver acceleration ranges from 10 g to 100 g,compared with the PLL that either loses lock or keeps tracking accuracy less than 33.89 Hz,the experimental results show that the proposed method can not only keep tracking,but also achieve tracking accuracy more than 2.77 Hz.
基金supported in part by the Spanish Ministry of Economy and Competitiveness and EU/FEDER(ESP201570014-C2-2-R)the International Science and Technology Cooperation Projects of Shanghai(No.17220730600)the ESA-MOST China Dragon5 Program(ID.58070)。
文摘The full constellation of Chinese Global Navigation Satellite System(GNSS)Bei Dou-3 has been deployed completely and started fully operational service.In addition to providing global Positioning,Navigation and Timing(PNT)services,the Bei Dou-3 satellites transmissions can also be used as the sources of illumination for Earth Observation(EO)with a bistatic radar configuration.This innovative EO concept,known as GNSS reflectometry(GNSS-R),allows to measure the Earth surface characteristics at high resolution via the reflected L-band radar signals collected by a constellation of small,low cost and low Earth orbiting satellites.For the first time in orbit,earth reflected Bei Dou-3 signal has been detected from the limited sets of raw data collected by the NASA’s Cyclone GNSS(CYGNSS)constellation.The feasibility of spaceborne Bei Dou-3 reflections on two typical applications,including sea surface wind and flooding inundation detection,has been demonstrated.The methodology and results give new strength to the prospect of new spaceborne GNSS-R instruments and missions,which can make multi-GNSS reflectometry observations available to better capture rapidly changing weather systems at better spatio-temporal scales.
基金supported by the State Key Laboratory of Geo-Information Engineering(SKLGIE2022-Z-2-1)the National Natural Science Foundation of China(41674024,42174036).
文摘Once the spoofer has controlled the navigation sys-tem of unmanned aerial vehicle(UAV),it is hard to effectively control the error convergence to meet the threshold condition only by adjusting parameters of estimation if estimation of the spoofer on UAV has continuous observation error.Aiming at this problem,the influence of the spoofer’s state estimation error on spoofing effect and error convergence conditions is theoretically analyzed,and an improved adaptively robust estimation algo-rithm suitable for steady-state linear quadratic estimator is pro-posed.It enables the spoofer’s estimator to reliably estimate UAV status in real time,improves the robustness of the estima-tor in responding to observation errors,and accelerates the con-vergence time of error control.Simulation experiments show that the mean value of normalized innovation squared(NIS)is reduced by 88.5%,and the convergence time of NIS value is reduced by 76.3%,the convergence time of true trajectory error of UAV is reduced by 42.3%,the convergence time of estimated trajectory error of UAV is reduced by 67.4%,the convergence time of estimated trajectory error of the spoofer is reduced by 33.7%,and the convergence time of broadcast trajectory error of the spoofer is reduced by 54.8%when the improved algorithm is used.The improved algorithm can make UAV deviate from pre-set trajectory to spoofing trajectory more effectively and more subtly.
基金funded by the National Natural Science Foundation of China(42030109).
文摘The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.
基金The National Natural Science Foundation of China(No.41974030)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX17_0150).
文摘A filter method that combines ensemble empirical modal decomposition(EEMD)and wavelet analysis methods was proposed to separate and correct the global navigation satellite system(GNSS)multipath error more effectively.In this method,the GNSS signal is first decomposed into several intrinsic mode functions(IMFs)and a residual through EEMD.Then,the IMFs and residual are classified into noise terms,mixed terms,and useful terms according to a combined classification criterion.Finally,the mixed term denoised by wavelet and the useful term are reconstructed to obtain the multipath error and thus enable an error correction model to be built.The measurement data provided by the Curtin GNSS Research Center were used for processing and analysis.Results show that the proposed method can separate multipath error from GNSS data to a great extent,thereby effectively addressing the defects of EEMD and wavelet methods on multipath error weakening.The error correction model established with the separated multipath error has a higher accuracy and provides a certain reference value for research on related signal processing.
基金the research project titled"Implementation of Deep Learning Algorithms to Develop Web based Ionospheric Time Delays Forecasting System over Indian Region using Ground based GNSS and NAVigation with Indian Constellation(NAVIC)observations"sponsored by Science&Engineering Research Board(SERB)(A statutory body of the Department of Science&Technology,Government of India,New Delhi,India,vide sanction order No:ECR/2018/001701Department of Science and Technology,New Delhi,India for funding this research through SR/FST/ESI-130/2013(C)FIST program
文摘Global Positioning System(GPS)services could be improved through prediction of ionospheric delays for satellite-based radio signals.With respect to latitude,longitude,local time,season,solar cycle and geomagnetic activity the Total Electron Content(TEC)have significant variations in both time and space.These temporal and spatial TEC variations driven by interplanetary space weather conditions such as solar and geomagnetic activities can degrade the communication and navigation links of GPS.Hence,in this paper,performance of TEC forecasting models based on Neural Networks(NN)have been evaluated to forecast(1-h ahead)ionospheric TEC over equatorial low latitude Bengaluru e12:97+N;77:59+ET,Global Navigation Satellite System(GNSS)station,India.The VTEC data is collected for 2009 e2016(8 years)during current 24 th solar cycle.The input space for the NN models comprise the solar Extreme UV flux,F10.7 proxy,a geomagnetic planetary A index(AP)index,sunspot number(SSN),disturbance storm time(DST)index,solar wind speed(Vsw),solar wind proton density(Np),Interplanetary Magnetic Field(IMF Bz).The performance of NN based TEC forecast models and International Reference Ionosphere,IRI-2016 global TEC model has evaluated during testing period,2016.The NN based model driven by all the inputs,which is a NN unified model(NNunq)has shown better accuracy with Mean Absolute Error(MAE)of 3.15 TECU,Mean Square Deviation(MSD)of 16.8 and Mean Absolute Percentage Error(MAPE)of 19.8%and is 1 e25%more accurate than the other NN based TEC forecast models(NN1,NN2 and NN3)and IRI-2016 model.NNunq model has less Root Mean Square Error(RMSE)value 3.8 TECU and highest goodness-of-fit(R2)with 0.85.The experimental results imply that NNunq/NN1 model forecasts ionospheric TEC accurately across equatorial low-latitude GNSS station and IRI-2016 model performance is necessarily improved as its forecast accuracy is limited to 69 e70%.
