Traditional orthogonal strapdown inertial navigation sys-tem （SINS） cannot achieve satisfactory self-alignment accuracy in the stationary base： taking more than 5 minutes and al the iner-tial sensors biases cannot ...Traditional orthogonal strapdown inertial navigation sys-tem （SINS） cannot achieve satisfactory self-alignment accuracy in the stationary base： taking more than 5 minutes and al the iner-tial sensors biases cannot get ful observability except the up-axis accelerometer. However, the ful skewed redundant SINS （RSINS） can not only enhance the reliability of the system, but also improve the accuracy of the system, such as the initial alignment. Firstly, the observability of the system state includes attitude errors and al the inertial sensors biases are analyzed with the global perspective method： any three gyroscopes and three accelerometers can be assembled into an independent subordinate SINS （sub-SINS）;the system state can be uniquely confirmed by the coupling connec-tions of al the sub-SINSs;the attitude errors and random constant biases of al the inertial sensors are observable. However, the ran-dom noises of the inertial sensors are not taken into account in the above analyzing process. Secondly, the ful-observable Kalman filter which can be applied to the actual RSINS containing random noises is established; the system state includes the position, ve-locity, attitude errors of al the sub-SINSs and the random constant biases of the redundant inertial sensors. At last, the initial self-alignment process of a typical four-redundancy ful skewed RSINS is simulated： the horizontal attitudes （pitch, rol ） errors and yaw error can be exactly evaluated within 80 s and 100 s respectively, while the random constant biases of gyroscopes and accelero-meters can be precisely evaluated within 120 s. For the ful skewed RSINS, the self-alignment accuracy is greatly improved, mean-while the self-alignment time is widely shortened.展开更多
To study the parameter estimating effects of a free-floating tumbling space target,the extended Kalman filter(EKF)scheme is utilized with different high-nonlinear translational and rotational coupled kinematic&dyn...To study the parameter estimating effects of a free-floating tumbling space target,the extended Kalman filter(EKF)scheme is utilized with different high-nonlinear translational and rotational coupled kinematic&dynamic models on the LIDAR measurements.Applying the aforementioned models and measurements results in the situation where one single state can be estimated differently with varying accuracies since the EKFs based on different models have different observabilities.In the proposed EKFs,the traditional quaternions based kinematics and dynamics and the dual vector quaternions(DVQ)based kinematics and dynamics are used for the modeling of the relative motions between a chaser satellite and an uncooperative target.In the non-contact estimating scenarios,only highly nonlinear relative attitude and range measurements:the grapple fixture on the target measured from the chaser satellite via vision-based sensors,can be used.By evaluating the results of the EKFs,the observability properties of each EKF are studied analytically and numerically with the the Observability Gramian matrices(OG)and the standard deviations for every estimated parameters.The analysis of observability perform intensive studies and reveal the intrinsic factors that affect the accuracy and stability of the parameters estimation of an uncooperative space target.Finally,the analytical and numerical results show the optimal composition of the kinematic&dynamic models and measurements.展开更多
An efficient observability analysis method is proposed to enable online detection of performance degradation of an optimization-based sliding window visual-inertial state estimation framework.The proposed methodology ...An efficient observability analysis method is proposed to enable online detection of performance degradation of an optimization-based sliding window visual-inertial state estimation framework.The proposed methodology leverages numerical techniques in nonlinear observability analysis to enable online evaluation of the system observability and indication of the state estimation performance.Specifically,an empirical observability Gramian based approach is introduced to efficiently measure the observability condition of the windowed nonlinear system,and a scalar index is proposed to quantify the average system observability.The proposed approach is specialized to a challenging optimizationbased sliding window monocular visual-inertial state estimation formulation and evaluated through simulation and experiments to assess the efficacy of the methodology.The analysis result shows that the proposed approach can correctly indicate degradation of the state estimation accuracy with real-time performance.展开更多
Passive localization by a single moving observer using Time of Arrival(TOA)only with an unknown Signal Repetition Interval(SRI)is investigated in this paper.Observability analysis is performed first.The observability ...Passive localization by a single moving observer using Time of Arrival(TOA)only with an unknown Signal Repetition Interval(SRI)is investigated in this paper.Observability analysis is performed first.The observability condition for uniquely determining the emitter position and SRI is derived.The conditional Cramer-Rao Lower Bound(CRLB)is also analyzed.It is found that the ambiguity of the SRI integer of the first TOA does not affect the theoretical estimation precision of the emitter position and SRI.A Reference-Fixed Differential TOA(RFDTOA)-based Iterative Maximum Likelihood Estimator(IMLE)is proposed,which only needs O(M)computational operations.Theoretical analysis and simulation results show that the Mean Square Error(MSE)of the proposed algorithm could attain the CRLB with moderate Gaussian measurement noise.展开更多
A methodology is proposed to enable real-time evaluation of the observability of local motions,and generate a local observability cost map to enable informed local motion planning in order to avoid potential degradati...A methodology is proposed to enable real-time evaluation of the observability of local motions,and generate a local observability cost map to enable informed local motion planning in order to avoid potential degradation or degeneracy in state estimator performance.The proposed approach leverages efficient numerical techniques in nonlinear observability analysis and motion primitive-based planning technique to realize the local observability prediction with real-time performance.The degradation of the state estimation performance can be readily predicted with the local observability evaluation result.The proposed approach is specialized to a representative optimization-based monocular visual-inertial state estimation formulation and evaluated through simulation and experiments.The experimental results demonstrated the ability of the proposed methodology to correctly anticipate the potential state estimation degradation.展开更多
The interception information of infrared（ IR）-guided air-to-air missiles（ AAM） is mainly estimated only using the basic bearing measurements. In order to intercept highly maneuverable targets,it is essential to st...The interception information of infrared（ IR）-guided air-to-air missiles（ AAM） is mainly estimated only using the basic bearing measurements. In order to intercept highly maneuverable targets,it is essential to study the system observability to improve the target tracking system performance.The uniqueness of this paper is that the observability analysis is derived based on a discrete three-dimensional （3D） system model. During the maneuvering scenario,the system is approximated by a segment-by-segment system. The relationship between missile-target motion and observability is given by direct and dual approaches. Meanwhile sufficient observability conditions are derived. Moreover,a numerical simulation is conducted and an alternate method is provided to reinforce the proposed observability analysis results.展开更多
An active perception methodology is proposed to locally predict the observability condition in a reasonable horizon and suggest an observability-constrained motion direction for the next step to ensure an accurate and...An active perception methodology is proposed to locally predict the observability condition in a reasonable horizon and suggest an observability-constrained motion direction for the next step to ensure an accurate and consistent state estimation performance of vision-based navigation systems. The methodology leverages an efficient EOG-based observability analysis and a motion primitive-based path sampling technique to realize the local observability prediction with a real-time performance. The observability conditions of potential motion trajectories are evaluated,and an informed motion direction is selected to ensure the observability efficiency for the state estimation system. The proposed approach is specialized to a representative optimizationbased monocular vision-based state estimation formulation and demonstrated through simulation and experiments to evaluate the ability of estimation degradation prediction and efficacy of motion direction suggestion.展开更多
The target motion analysis（TMA） for a moving scanning emitter with known fixed scan rate by a single observer using the time of interception（TOI） measurements only is investigated in this paper.By transforming the...The target motion analysis（TMA） for a moving scanning emitter with known fixed scan rate by a single observer using the time of interception（TOI） measurements only is investigated in this paper.By transforming the TOI of multiple scan cycles into the direction difference of arrival（DDOA） model,the observability analysis for the TMA problem is performed.Some necessary conditions for uniquely identifying the scanning emitter trajectory are obtained.This paper also proposes a weighted instrumental variable（WIV） estimator for the scanning emitter TMA,which does not require any initial solution guess and is closed-form and computationally attractive.More importantly,simulations show that the proposed algorithm can provide estimation mean square error close to the Cramer-Rao lower bound（CRLB） at moderate noise levels with significantly lower estimation bias than the conventional pseudo-linear least square（PLS） estimator.展开更多
Observability analysis(OA)is vital to obtaining the available input measurements of state estimation(SE)in an integrated electricity and heating system(IEHS).Considering the thermal quasi-dynamics in pipelines,the mea...Observability analysis(OA)is vital to obtaining the available input measurements of state estimation(SE)in an integrated electricity and heating system(IEHS).Considering the thermal quasi-dynamics in pipelines,the measurement equations in heating systems are dependent on the estimated results,leading to an interdependency between OA and SE.Conventional OA methods require measurement equations be known exactly before SE is performed,and they are not applicable to IEHSs.To bridge this gap,a scenario-based OA scheme for IEHSs is devised that yields reliable analysis results for a predefined set of time-delay scenarios to cope with this interdependency.As its core procedure,the observable state identification and observability restoration are formulated in terms of integer linear programming.Numerical tests are conducted to demonstrate the validity and superiority of the proposed formulation.展开更多
As one of the most severe typhoons in the year 2005,Typhoon Longwang is chosen as a case study in this article.Throughout its life,two surveillance flights are carried out on it.Different from previous studies,GPS(glo...As one of the most severe typhoons in the year 2005,Typhoon Longwang is chosen as a case study in this article.Throughout its life,two surveillance flights are carried out on it.Different from previous studies,GPS(global positioning system)Dropwinsonde data collected from the Dropwinsonde Observations for Typhoon Surveillance near the Taiwan Region is chosen to present the thermodynamic and kinetic structure at its two different stages of development.This study suggests that not only kinetic structure but also thermodynamic structure of Longwang are more robust in the second surveillance than the first surveillance,with stronger and larger circulation and a warmer core.Further research shows that the environmental vertical wind shear mainly contributes to the asymmetric structure of the typhoon.The strong vertical wind shear not only results in the distinct asymmetric structure,but also restrains the development of the typhoon.展开更多
Objective In order to reduce the interfering noise from the earth surface, scientists have carried out multi-geophysical borehole observations and the related study. This study aims at improving signal-to-noise ratio ...Objective In order to reduce the interfering noise from the earth surface, scientists have carried out multi-geophysical borehole observations and the related study. This study aims at improving signal-to-noise ratio obtained from the observation data to obtain zero noise data, which will be of great help to improve geophysical studies. Insights from this study will be significant for the earthquake disaster reduction, resource exploration and environmental protection.展开更多
The spatial variation and diurnal fluctuation of sea surface wind over the Qiongzhou Strait were described using verified datasets from automatic weather stations on board a ferry, buoys, and on the coast. Results are...The spatial variation and diurnal fluctuation of sea surface wind over the Qiongzhou Strait were described using verified datasets from automatic weather stations on board a ferry, buoys, and on the coast. Results are as follows： （1） On average, sea surface wind speed is 34 m/s larger over the Qiongzhou Strait than in the coastal area. Sea surface wind speeds of 8.0 rrds or above （on Beaufort scale five） in the coastal area are associated with speeds 5-6 m/s greater over the surface of the Qiongzhou Strait. （2） Gust coefficients for the Qiongzhou Strait decrease along with increasing wind speeds. When coastal wind speed is less than scale five, the average gust coefficient over the sea surface is between 1.4 and 1.5; when wind speed is equal to scale five or above, the average gust coefficient is about 1.35. （3） In autumn and winter, the diurnal differences of average wind speed and wind consistency over the strait are less than those in the coastal area; when wind speed is 10.8 m/s （scale six） or above, the diurnal difference of average wind speed decreases while wind consistency increases for both the strait and the coast.展开更多
In order to effectively defend against the threats of the hypersonic gliding vehicles(HGVs),HGVs should be tracked as early as possible,which is beyond the capability of the ground-based radars.Being benefited by the ...In order to effectively defend against the threats of the hypersonic gliding vehicles(HGVs),HGVs should be tracked as early as possible,which is beyond the capability of the ground-based radars.Being benefited by the developing megaconstellations in low-Earth orbit,this paper proposes a relay tracking mode to track HGVs to overcome the above problem.The whole tracking mission is composed of several tracking intervals with the same duration.Within each tracking interval,several appropriate satellites are dispatched to track the HGV.Satellites that are planned to take part in the tracking mission are selected by a new derived observability criterion.The tracking performances of the proposed tracking mode and the other two traditional tracking modes,including the stare and track-rate modes,are compared by simulation.The results show that the relay tracking mode can track the whole trajectory of a HGV,while the stare mode can only provide a very short tracking arc.Moreover,the relay tracking mode achieve higher tracking accuracy with fewer attitude controls than the track-rate mode.展开更多
We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we ...We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we also use a model consisting of a black body and a power law to fit the spectra. We find that for the latter model there are indications of an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs, like （a） temperatures of the blackbodies are strongly correlated with each other, （b） fluxes in the black body components are strongly correlated with each other, （c） the temperatures of the black body trace the profile of the individual pulses of the GRBs, and （d） the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.展开更多
Since the promulgation and implementation of "Learning and Development Guide for Children Aged 3-6" for 10 years, teachers have deeply realized that games play an important role in the implementation of kind...Since the promulgation and implementation of "Learning and Development Guide for Children Aged 3-6" for 10 years, teachers have deeply realized that games play an important role in the implementation of kindergarten curriculum in the process of kindergarten curriculum reform, and gradually turned their attention to children and their game activities, paying attention to their behaviors, emotions and experiences in games. As an integral part of kindergarten education, regional game activities have become an important way for children to learn and develop. Then, how to observe children, record children, analyze childrens game behavior in regional games, and then support and guide childrens development has become a big problem in teachers professional growth. Therefore, under the guidance of the subject, our garden has reorganized the regional observation cases, carried out relevant training, conducted kindergarten-based teaching and research, reviewed teachers observation behaviors and records, identified the problems, clearly positioned them, and gradually adjusted them, so as to improve teachers game observation and record level, so as to support teachers to play a guiding role in childrens game activities.展开更多
To solve the problem that external systematic errors of the optical camera cannot be fully estimated due to limited computing resources,a unified dimensionality reduction representation method for the external systema...To solve the problem that external systematic errors of the optical camera cannot be fully estimated due to limited computing resources,a unified dimensionality reduction representation method for the external systematic errors of the optical camera is proposed,and autonomous relative optical navigation is realized.The camera translational and misalignment errors are converted into a three-dimensional rotation error,whose differential model can be established through specific attitude control and appropriate assumption.Then,the rotation error and the relative motion state are jointly estimated in an augmented Kalman filter framework.Compared with the traditional method that estimates the camera translational and misalignment errors,the proposed method reduces the computational complexity in that the estimated state dimension is reduced.Furthermore,as demonstrated by numerical simulation,the estimation accuracy is improved significantly.展开更多
An energy transference from unsteady flow of the incompressible viscous fluid is proposed with radiative heat flux.In order to develop an efficient mathematical model,Rosseland estimation and Boussinesq approximation ...An energy transference from unsteady flow of the incompressible viscous fluid is proposed with radiative heat flux.In order to develop an efficient mathematical model,Rosseland estimation and Boussinesq approximation have been employed.An efficient mathematical model for energy transfer from unsteady flow of viscous fluid is established by means of newly presented fractional differential operator.The fractional differential operator has the capability to describe memory for energy transfer and hereditary properties based on its kernel for minimization or maximization of thermal performance within thermophysical features.The developed model for unsteady flow of viscous fluid is investigated for velocity,concentration and temperature via Fourier and statistical approaches.The analytical results have been simulated for the rheological parameters and statistical results are depicted for different types of graphs for knowing identical and proportional quantity of energy transference.展开更多
In the process of initial alignment for a strapdown inertial navigation system （SINS） on a stationary base, the east gyro drift rate is an important factor affecting the alignment accuracy of the azimuth misalignmen...In the process of initial alignment for a strapdown inertial navigation system （SINS） on a stationary base, the east gyro drift rate is an important factor affecting the alignment accuracy of the azimuth misalignment angle. When the Kalman filtering algorithm is adopted in initial alignment, it yields a constant error in the estimation of the azimuth misalignment angle because the east gyro drift rate cannot be estimated. To improve the alignment accuracy, a novel alignment method on revolving mounting base is proposed. The Kalman filtering algorithm of extending the measured values is studied. The theory of spectral condition number is utilized to analyze the degrees of observability of states. Simulation results show that the estimation accuracy of the azimuth misalignment angle is greatly improved through revolving mounting base, and the proposed method is efficient in initial alignment for a medium accurate SINS.展开更多
Aiming at the problem of relative navigation for non-cooperative rendezvous of spacecraft,this paper proposes a new angles-only navigation architecture using non-linear dynamics method. This method does not solve the ...Aiming at the problem of relative navigation for non-cooperative rendezvous of spacecraft,this paper proposes a new angles-only navigation architecture using non-linear dynamics method. This method does not solve the problem of poor observability of angles-only navigation through orbital or attitude maneuvering,but improves the observability of angles-only navigation through capturing the non-linearity of the system in the evolution of relative motion. First,three relative dynamics models and their corresponding line-of-sight(LoS)measurement equations are introduced,including the rectilinear state relative dynamics model,the curvilinear state relative dynamics model,and the relative orbital elements(ROE)state relative dynamics model. Then,an observability analysis theory based on the Gramian matrix is introduced to determine which relative dynamics model could maximize the observability of angles-only navigation. Next,an adaptive extended Kalman filtering scheme is proposed to solve the problem that the angles-only navigation filter using the non-linear dynamics method is sensitive to measurement noises. Finally,the performances of the proposed angles-only navigation architecture are tested by means of numerical simulations,which demonstrates that the angles-only navigation filtering scheme without orbital or attitude maneuvering is completely feasible through improving the modeling of the relative dynamics and LoS measurement equations.展开更多
Transfer alignment is used to initialize SINS(Strapdown Inertial Navigation System)in motion.Lever-arm effect compensation is studied existing in an AUV(Autonomous Underwater Vehicle)before launched from the mother sh...Transfer alignment is used to initialize SINS(Strapdown Inertial Navigation System)in motion.Lever-arm effect compensation is studied existing in an AUV(Autonomous Underwater Vehicle)before launched from the mother ship.The AUV is equipped with SINS,Doppler Velocity Log,depth sensor and other navigation sensors.The lever arm will cause large error on the transfer alignment between master inertial navigation system and slave inertial navigation system,especially in big ship situations.This paper presents a novel method that can effectively estimate and compensate the flexural lever arm between the main inertial navigation system mounted on the mother ship and the slave inertial navigation system equipped on the AUV.The nonlinear measurement equation of angular rate is derived based on three successive rotations of the body frame of the master inertial navigation system.Nonlinear filter is utilized as the nonlinear estimator for its capability of non-linear approximation.Observability analysis was conducted on the SINS state vector based on singular value decomposition method.State equation of SINS was adopted as the system state equation.Simulation experiments were conducted and results showed that the proposed method can estimate the flexural lever arm more accurately,the precision of transfer alignment was improved and alignment time was shortened accordingly.展开更多
基金supported by the National Defense PreResearch Foundation of China(51309030102)
文摘Traditional orthogonal strapdown inertial navigation sys-tem （SINS） cannot achieve satisfactory self-alignment accuracy in the stationary base： taking more than 5 minutes and al the iner-tial sensors biases cannot get ful observability except the up-axis accelerometer. However, the ful skewed redundant SINS （RSINS） can not only enhance the reliability of the system, but also improve the accuracy of the system, such as the initial alignment. Firstly, the observability of the system state includes attitude errors and al the inertial sensors biases are analyzed with the global perspective method： any three gyroscopes and three accelerometers can be assembled into an independent subordinate SINS （sub-SINS）;the system state can be uniquely confirmed by the coupling connec-tions of al the sub-SINSs;the attitude errors and random constant biases of al the inertial sensors are observable. However, the ran-dom noises of the inertial sensors are not taken into account in the above analyzing process. Secondly, the ful-observable Kalman filter which can be applied to the actual RSINS containing random noises is established; the system state includes the position, ve-locity, attitude errors of al the sub-SINSs and the random constant biases of the redundant inertial sensors. At last, the initial self-alignment process of a typical four-redundancy ful skewed RSINS is simulated： the horizontal attitudes （pitch, rol ） errors and yaw error can be exactly evaluated within 80 s and 100 s respectively, while the random constant biases of gyroscopes and accelero-meters can be precisely evaluated within 120 s. For the ful skewed RSINS, the self-alignment accuracy is greatly improved, mean-while the self-alignment time is widely shortened.
文摘To study the parameter estimating effects of a free-floating tumbling space target,the extended Kalman filter(EKF)scheme is utilized with different high-nonlinear translational and rotational coupled kinematic&dynamic models on the LIDAR measurements.Applying the aforementioned models and measurements results in the situation where one single state can be estimated differently with varying accuracies since the EKFs based on different models have different observabilities.In the proposed EKFs,the traditional quaternions based kinematics and dynamics and the dual vector quaternions(DVQ)based kinematics and dynamics are used for the modeling of the relative motions between a chaser satellite and an uncooperative target.In the non-contact estimating scenarios,only highly nonlinear relative attitude and range measurements:the grapple fixture on the target measured from the chaser satellite via vision-based sensors,can be used.By evaluating the results of the EKFs,the observability properties of each EKF are studied analytically and numerically with the the Observability Gramian matrices(OG)and the standard deviations for every estimated parameters.The analysis of observability perform intensive studies and reveal the intrinsic factors that affect the accuracy and stability of the parameters estimation of an uncooperative space target.Finally,the analytical and numerical results show the optimal composition of the kinematic&dynamic models and measurements.
文摘An efficient observability analysis method is proposed to enable online detection of performance degradation of an optimization-based sliding window visual-inertial state estimation framework.The proposed methodology leverages numerical techniques in nonlinear observability analysis to enable online evaluation of the system observability and indication of the state estimation performance.Specifically,an empirical observability Gramian based approach is introduced to efficiently measure the observability condition of the windowed nonlinear system,and a scalar index is proposed to quantify the average system observability.The proposed approach is specialized to a challenging optimizationbased sliding window monocular visual-inertial state estimation formulation and evaluated through simulation and experiments to assess the efficacy of the methodology.The analysis result shows that the proposed approach can correctly indicate degradation of the state estimation accuracy with real-time performance.
基金supported by the National Natural Science Foundation of China(No.61901494).
文摘Passive localization by a single moving observer using Time of Arrival(TOA)only with an unknown Signal Repetition Interval(SRI)is investigated in this paper.Observability analysis is performed first.The observability condition for uniquely determining the emitter position and SRI is derived.The conditional Cramer-Rao Lower Bound(CRLB)is also analyzed.It is found that the ambiguity of the SRI integer of the first TOA does not affect the theoretical estimation precision of the emitter position and SRI.A Reference-Fixed Differential TOA(RFDTOA)-based Iterative Maximum Likelihood Estimator(IMLE)is proposed,which only needs O(M)computational operations.Theoretical analysis and simulation results show that the Mean Square Error(MSE)of the proposed algorithm could attain the CRLB with moderate Gaussian measurement noise.
文摘A methodology is proposed to enable real-time evaluation of the observability of local motions,and generate a local observability cost map to enable informed local motion planning in order to avoid potential degradation or degeneracy in state estimator performance.The proposed approach leverages efficient numerical techniques in nonlinear observability analysis and motion primitive-based planning technique to realize the local observability prediction with real-time performance.The degradation of the state estimation performance can be readily predicted with the local observability evaluation result.The proposed approach is specialized to a representative optimization-based monocular visual-inertial state estimation formulation and evaluated through simulation and experiments.The experimental results demonstrated the ability of the proposed methodology to correctly anticipate the potential state estimation degradation.
基金Supported by the National Natural Science Foundation of China(61333011)
文摘The interception information of infrared（ IR）-guided air-to-air missiles（ AAM） is mainly estimated only using the basic bearing measurements. In order to intercept highly maneuverable targets,it is essential to study the system observability to improve the target tracking system performance.The uniqueness of this paper is that the observability analysis is derived based on a discrete three-dimensional （3D） system model. During the maneuvering scenario,the system is approximated by a segment-by-segment system. The relationship between missile-target motion and observability is given by direct and dual approaches. Meanwhile sufficient observability conditions are derived. Moreover,a numerical simulation is conducted and an alternate method is provided to reinforce the proposed observability analysis results.
文摘An active perception methodology is proposed to locally predict the observability condition in a reasonable horizon and suggest an observability-constrained motion direction for the next step to ensure an accurate and consistent state estimation performance of vision-based navigation systems. The methodology leverages an efficient EOG-based observability analysis and a motion primitive-based path sampling technique to realize the local observability prediction with a real-time performance. The observability conditions of potential motion trajectories are evaluated,and an informed motion direction is selected to ensure the observability efficiency for the state estimation system. The proposed approach is specialized to a representative optimizationbased monocular vision-based state estimation formulation and demonstrated through simulation and experiments to evaluate the ability of estimation degradation prediction and efficacy of motion direction suggestion.
基金co-supported by the Shanghai Aerospace Science and Technology Innovation Fund of China(No.SAST2015028)the Equipment Prophecy Fund of China(No.9140A21040115KG01001)
文摘The target motion analysis（TMA） for a moving scanning emitter with known fixed scan rate by a single observer using the time of interception（TOI） measurements only is investigated in this paper.By transforming the TOI of multiple scan cycles into the direction difference of arrival（DDOA） model,the observability analysis for the TMA problem is performed.Some necessary conditions for uniquely identifying the scanning emitter trajectory are obtained.This paper also proposes a weighted instrumental variable（WIV） estimator for the scanning emitter TMA,which does not require any initial solution guess and is closed-form and computationally attractive.More importantly,simulations show that the proposed algorithm can provide estimation mean square error close to the Cramer-Rao lower bound（CRLB） at moderate noise levels with significantly lower estimation bias than the conventional pseudo-linear least square（PLS） estimator.
基金supported by National Natural Science Foundation of China(52177086)Fundamental Research Funds for the Central Universities(2023ZYGXZR063).
文摘Observability analysis(OA)is vital to obtaining the available input measurements of state estimation(SE)in an integrated electricity and heating system(IEHS).Considering the thermal quasi-dynamics in pipelines,the measurement equations in heating systems are dependent on the estimated results,leading to an interdependency between OA and SE.Conventional OA methods require measurement equations be known exactly before SE is performed,and they are not applicable to IEHSs.To bridge this gap,a scenario-based OA scheme for IEHSs is devised that yields reliable analysis results for a predefined set of time-delay scenarios to cope with this interdependency.As its core procedure,the observable state identification and observability restoration are formulated in terms of integer linear programming.Numerical tests are conducted to demonstrate the validity and superiority of the proposed formulation.
基金project of the National Science Foundation of China(40830958,40905020)project of National Basic Research Program of China(2009CB421502)+1 种基金project of the Special Scientific Research for Public Interest(GYHY201006007)project of the Specialized Research Fund for the Doctoral Program of Higher Education of China(20090091120038)
文摘As one of the most severe typhoons in the year 2005,Typhoon Longwang is chosen as a case study in this article.Throughout its life,two surveillance flights are carried out on it.Different from previous studies,GPS(global positioning system)Dropwinsonde data collected from the Dropwinsonde Observations for Typhoon Surveillance near the Taiwan Region is chosen to present the thermodynamic and kinetic structure at its two different stages of development.This study suggests that not only kinetic structure but also thermodynamic structure of Longwang are more robust in the second surveillance than the first surveillance,with stronger and larger circulation and a warmer core.Further research shows that the environmental vertical wind shear mainly contributes to the asymmetric structure of the typhoon.The strong vertical wind shear not only results in the distinct asymmetric structure,but also restrains the development of the typhoon.
基金supported by the National Science Foundation of China (grant No.1374052)
文摘Objective In order to reduce the interfering noise from the earth surface, scientists have carried out multi-geophysical borehole observations and the related study. This study aims at improving signal-to-noise ratio obtained from the observation data to obtain zero noise data, which will be of great help to improve geophysical studies. Insights from this study will be significant for the earthquake disaster reduction, resource exploration and environmental protection.
基金Research on the Pattern of gales over the Qiongzhou Strait and Forecasting Methods, a project of Natural Science Foundation of China (40765002)Forecasting System of Gales over the Qiongzhou Strait, a key science project for Hainan province (070302)
文摘The spatial variation and diurnal fluctuation of sea surface wind over the Qiongzhou Strait were described using verified datasets from automatic weather stations on board a ferry, buoys, and on the coast. Results are as follows： （1） On average, sea surface wind speed is 34 m/s larger over the Qiongzhou Strait than in the coastal area. Sea surface wind speeds of 8.0 rrds or above （on Beaufort scale five） in the coastal area are associated with speeds 5-6 m/s greater over the surface of the Qiongzhou Strait. （2） Gust coefficients for the Qiongzhou Strait decrease along with increasing wind speeds. When coastal wind speed is less than scale five, the average gust coefficient over the sea surface is between 1.4 and 1.5; when wind speed is equal to scale five or above, the average gust coefficient is about 1.35. （3） In autumn and winter, the diurnal differences of average wind speed and wind consistency over the strait are less than those in the coastal area; when wind speed is 10.8 m/s （scale six） or above, the diurnal difference of average wind speed decreases while wind consistency increases for both the strait and the coast.
基金supported by the Science and Technology Innovation Program of Hunan Province(2021RC3078)。
文摘In order to effectively defend against the threats of the hypersonic gliding vehicles(HGVs),HGVs should be tracked as early as possible,which is beyond the capability of the ground-based radars.Being benefited by the developing megaconstellations in low-Earth orbit,this paper proposes a relay tracking mode to track HGVs to overcome the above problem.The whole tracking mission is composed of several tracking intervals with the same duration.Within each tracking interval,several appropriate satellites are dispatched to track the HGV.Satellites that are planned to take part in the tracking mission are selected by a new derived observability criterion.The tracking performances of the proposed tracking mode and the other two traditional tracking modes,including the stare and track-rate modes,are compared by simulation.The results show that the relay tracking mode can track the whole trajectory of a HGV,while the stare mode can only provide a very short tracking arc.Moreover,the relay tracking mode achieve higher tracking accuracy with fewer attitude controls than the track-rate mode.
文摘We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we also use a model consisting of a black body and a power law to fit the spectra. We find that for the latter model there are indications of an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs, like （a） temperatures of the blackbodies are strongly correlated with each other, （b） fluxes in the black body components are strongly correlated with each other, （c） the temperatures of the black body trace the profile of the individual pulses of the GRBs, and （d） the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.
文摘Since the promulgation and implementation of "Learning and Development Guide for Children Aged 3-6" for 10 years, teachers have deeply realized that games play an important role in the implementation of kindergarten curriculum in the process of kindergarten curriculum reform, and gradually turned their attention to children and their game activities, paying attention to their behaviors, emotions and experiences in games. As an integral part of kindergarten education, regional game activities have become an important way for children to learn and develop. Then, how to observe children, record children, analyze childrens game behavior in regional games, and then support and guide childrens development has become a big problem in teachers professional growth. Therefore, under the guidance of the subject, our garden has reorganized the regional observation cases, carried out relevant training, conducted kindergarten-based teaching and research, reviewed teachers observation behaviors and records, identified the problems, clearly positioned them, and gradually adjusted them, so as to improve teachers game observation and record level, so as to support teachers to play a guiding role in childrens game activities.
基金supported by National Natural Science Foundation of China(Nos.U20B2055 and 61525301)Graduate Research Innovation Projects of Hunan Province,China(No.CX20210013)。
文摘To solve the problem that external systematic errors of the optical camera cannot be fully estimated due to limited computing resources,a unified dimensionality reduction representation method for the external systematic errors of the optical camera is proposed,and autonomous relative optical navigation is realized.The camera translational and misalignment errors are converted into a three-dimensional rotation error,whose differential model can be established through specific attitude control and appropriate assumption.Then,the rotation error and the relative motion state are jointly estimated in an augmented Kalman filter framework.Compared with the traditional method that estimates the camera translational and misalignment errors,the proposed method reduces the computational complexity in that the estimated state dimension is reduced.Furthermore,as demonstrated by numerical simulation,the estimation accuracy is improved significantly.
文摘An energy transference from unsteady flow of the incompressible viscous fluid is proposed with radiative heat flux.In order to develop an efficient mathematical model,Rosseland estimation and Boussinesq approximation have been employed.An efficient mathematical model for energy transfer from unsteady flow of viscous fluid is established by means of newly presented fractional differential operator.The fractional differential operator has the capability to describe memory for energy transfer and hereditary properties based on its kernel for minimization or maximization of thermal performance within thermophysical features.The developed model for unsteady flow of viscous fluid is investigated for velocity,concentration and temperature via Fourier and statistical approaches.The analytical results have been simulated for the rheological parameters and statistical results are depicted for different types of graphs for knowing identical and proportional quantity of energy transference.
文摘In the process of initial alignment for a strapdown inertial navigation system （SINS） on a stationary base, the east gyro drift rate is an important factor affecting the alignment accuracy of the azimuth misalignment angle. When the Kalman filtering algorithm is adopted in initial alignment, it yields a constant error in the estimation of the azimuth misalignment angle because the east gyro drift rate cannot be estimated. To improve the alignment accuracy, a novel alignment method on revolving mounting base is proposed. The Kalman filtering algorithm of extending the measured values is studied. The theory of spectral condition number is utilized to analyze the degrees of observability of states. Simulation results show that the estimation accuracy of the azimuth misalignment angle is greatly improved through revolving mounting base, and the proposed method is efficient in initial alignment for a medium accurate SINS.
基金supported by the China Aerospace Science and Technology Corporation Eighth Research Institute Industry-University-Research Cooperation Fund(No.SAST 2020-019)。
文摘Aiming at the problem of relative navigation for non-cooperative rendezvous of spacecraft,this paper proposes a new angles-only navigation architecture using non-linear dynamics method. This method does not solve the problem of poor observability of angles-only navigation through orbital or attitude maneuvering,but improves the observability of angles-only navigation through capturing the non-linearity of the system in the evolution of relative motion. First,three relative dynamics models and their corresponding line-of-sight(LoS)measurement equations are introduced,including the rectilinear state relative dynamics model,the curvilinear state relative dynamics model,and the relative orbital elements(ROE)state relative dynamics model. Then,an observability analysis theory based on the Gramian matrix is introduced to determine which relative dynamics model could maximize the observability of angles-only navigation. Next,an adaptive extended Kalman filtering scheme is proposed to solve the problem that the angles-only navigation filter using the non-linear dynamics method is sensitive to measurement noises. Finally,the performances of the proposed angles-only navigation architecture are tested by means of numerical simulations,which demonstrates that the angles-only navigation filtering scheme without orbital or attitude maneuvering is completely feasible through improving the modeling of the relative dynamics and LoS measurement equations.
基金This work is funded by Natural Science Foundation of Jiangsu Province under Grant BK20160955a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions and Science Research Foundation of Nanjing University of Information Science and Technology under Grant 20110430+1 种基金Open Foundation of Jiangsu Key Laboratory of Meteorological Observation and Information Processing(KDXS1304)Open Foundation of Jiangsu Key Laboratory of Ocean Dynamic Remote Sensing and Acoustics(KHYS1405).
文摘Transfer alignment is used to initialize SINS(Strapdown Inertial Navigation System)in motion.Lever-arm effect compensation is studied existing in an AUV(Autonomous Underwater Vehicle)before launched from the mother ship.The AUV is equipped with SINS,Doppler Velocity Log,depth sensor and other navigation sensors.The lever arm will cause large error on the transfer alignment between master inertial navigation system and slave inertial navigation system,especially in big ship situations.This paper presents a novel method that can effectively estimate and compensate the flexural lever arm between the main inertial navigation system mounted on the mother ship and the slave inertial navigation system equipped on the AUV.The nonlinear measurement equation of angular rate is derived based on three successive rotations of the body frame of the master inertial navigation system.Nonlinear filter is utilized as the nonlinear estimator for its capability of non-linear approximation.Observability analysis was conducted on the SINS state vector based on singular value decomposition method.State equation of SINS was adopted as the system state equation.Simulation experiments were conducted and results showed that the proposed method can estimate the flexural lever arm more accurately,the precision of transfer alignment was improved and alignment time was shortened accordingly.
