Hyper-and multi-spectral image fusion is an important technology to produce hyper-spectral and hyper-resolution images,which always depends on the spectral response function andthe point spread function.However,few wo...Hyper-and multi-spectral image fusion is an important technology to produce hyper-spectral and hyper-resolution images,which always depends on the spectral response function andthe point spread function.However,few works have been payed on the estimation of the two degra-dation functions.To learn the two functions from image pairs to be fused,we propose a Dirichletnetwork,where both functions are properly constrained.Specifically,the spatial response function isconstrained with positivity,while the Dirichlet distribution along with a total variation is imposedon the point spread function.To the best of our knowledge,the neural network and the Dirichlet regularization are exclusively investigated,for the first time,to estimate the degradation functions.Both image degradation and fusion experiments demonstrate the effectiveness and superiority of theproposed Dirichlet network.展开更多
Because of descriptive nonlinearity and computational inefficiency,topology optimization with fatigue life under aperiodic loads has developed slowly.A fatigue constraint topology optimization method based on bidirect...Because of descriptive nonlinearity and computational inefficiency,topology optimization with fatigue life under aperiodic loads has developed slowly.A fatigue constraint topology optimization method based on bidirectional evolutionary structural optimization(BESO)under an aperiodic load is proposed in this paper.In viewof the severe nonlinearity of fatigue damagewith respect to design variables,effective stress cycles are extracted through transient dynamic analysis.Based on the Miner cumulative damage theory and life requirements,a fatigue constraint is first quantified and then transformed into a stress problem.Then,a normalized termination criterion is proposed by approximatemaximum stress measured by global stress using a P-normaggregation function.Finally,optimization examples show that the proposed algorithm can not only meet the requirements of fatigue life but also obtain a reasonable configuration.展开更多
Radio frequency signal compatibility is the basis of interoperability of the Satellite eBased Augmentation System(SBAS).SBAS should abide by relative international radio regulations of International Telecommunication ...Radio frequency signal compatibility is the basis of interoperability of the Satellite eBased Augmentation System(SBAS).SBAS should abide by relative international radio regulations of International Telecommunication Union(ITU) and meet the compatibility requirements of radio frequency signal between the Global Navigation Satellite System(GNSS)/SBAS,in order to avoid negative mutual interference.According to ITU Proposal and related reference and assumptions,the paper made simulation of signal receiving maximum power in the Bei Dou Satellite-Based Augmentation System(BDSBAS)global signal coverage.And then,interference of BDSBAS to Global Positioning System(GPS)/WAAS(Wide Area Augmentation System) on L1/L5 bands were calculated and analyzed,with equivalent carrierto-noise ratio as the evaluation parameter.The result shows that the carrier-to-noise ratio decrease of GPS/WAAS caused by BDSBAS B1 C and B2 a signals are extremely lower than inter-system interference of GPS/WAAS,and thus can be ignored in practical applications.Therefore,BDSBAS will not cause the service performance degradation of GPS and WAAS.展开更多
On-Line Analytical Processing (OLAP) is based on pre-computation of data cubes, which greatly reduces the response time and improves the performance of OLAP. Frag-Shells algorithm is a common method of precomputation....On-Line Analytical Processing (OLAP) is based on pre-computation of data cubes, which greatly reduces the response time and improves the performance of OLAP. Frag-Shells algorithm is a common method of precomputation.However, it relies too much on the data dispersion that it performs poorly, when confronts large amount of highly disperse data. As the amount of data grows fast nowadays, the efficiency of data cube construction is increasingly becoming a significant bottleneck. In addition, with the popularity of cloud computing and big data, MapReduce framework proposed by Google is playing an increasingly prominent role in parallel processing. It is an intuitive idea that MapReduce framework can be used to enhance the efficiency of parallel data cube construction. In this paper, by improving the Frag-Shells algorithm based on the irrelevance of data dispersion, and taking advantages of the high parallelism of MapReduce framework, we propose an improved Frag-Shells algorithm based on MapReduce framework. The simulation results prove that the proposed algorithm greatly enhances the efficiency of cube construction.展开更多
As a means of copyright protection for multimedia data, digital watermarking technology has attracted more and more attention in various research fields. Researchers have begun to explore the feasibility of applying i...As a means of copyright protection for multimedia data, digital watermarking technology has attracted more and more attention in various research fields. Researchers have begun to explore the feasibility of applying it to remote sensing data recently. Because of the particularity of remote sensing image, higher requirements are put forward for its security and management, especially for the copyright protection, illegal use and authenticity identification of remote sensing image data. Therefore, this paper proposes to use image watermarking technology to achieve comprehensive security protection of remote sensing image data, while the use of cryptography technology increases the applicability and security of watermarking technology. The experimental results show that the scheme of remote sensing image digital watermarking technology has good performance in the imperceptibility and robustness of watermarking.展开更多
Multipath and continuous wave (CW) interference may cause severe performance degradation of global navigation satellite system (GNSS) receivers. This paper analyzes the code tracking performance of early-minus-late po...Multipath and continuous wave (CW) interference may cause severe performance degradation of global navigation satellite system (GNSS) receivers. This paper analyzes the code tracking performance of early-minus-late power (EMLP) discriminator of GNSS receivers in the presence of multipath and CW interference. An analytical expression of the code tracking error is suggested for EMLP discriminator, and it can be used to assess the effect of multipath and CW interference. The derived expression shows that the combined effects include three components: multipath component;CW interference component and the combined component of multipath and CW interference. The effect of these components depends on some factors which can be classified into two categories: the receiving environment and the receiver parameters. Numerical results show how these factors affect the tracking performances. It is shown that the proper receiver parameters can suppress the combined effects of multipath and CW interference.展开更多
The electromagnetic satellite Zhangheng 01(ZH-01) was successfully launched on February 2, 2018. The GNSS Radio Occultation(GRO) receiver on board the satellite is able to observe the occultation events of GPS and Bei...The electromagnetic satellite Zhangheng 01(ZH-01) was successfully launched on February 2, 2018. The GNSS Radio Occultation(GRO) receiver on board the satellite is able to observe the occultation events of GPS and BeiDou navigation satellites. We analyzed the data acquired during the in-orbit testing period. We concludes that the GRO ionosphere inversion results are reasonable,the trend is correct, the satellite can observe about 600 ionosphere occultation events each day. The global coverage of more than 30000 consecutive GRO events in more than two months were analyzed and compared with COSMIC observations: both the GRO and COSMIC occultation can realize global coverage: the Nm F2 and Hm F2 global distributions are similar and change obviously with latitude. We used three digisondes at different latitudes to analyze and compare the spatio-temporally consistent GRO data: the RMSE of GRO Nm F2 relative to digisonde is better than 9.41%, the correlation coefficient is better than 0.8682: the relative RMSE of Hm F2 is better than 7.80% and the correlation coefficient is better than 0.7066.展开更多
China's remote sensing satellite applications started in the 1960s by processing and using foreign satellite data.In the 1990s,China launched its first meteorological satellite,and focused on the construction of C...China's remote sensing satellite applications started in the 1960s by processing and using foreign satellite data.In the 1990s,China launched its first meteorological satellite,and focused on the construction of Chinese remote sensing satellites and ground application systems.The development of China's remote sensing satellite system focuses展开更多
The next generation of High Throughput Satellite(HTS)will exploit Q/V band for the feeder link and Ka band for the user link.The exploitation of multiple gateways(GWs)is a transmit diversity measure to compensate seve...The next generation of High Throughput Satellite(HTS)will exploit Q/V band for the feeder link and Ka band for the user link.The exploitation of multiple gateways(GWs)is a transmit diversity measure to compensate severe rain attenuation of Q/V band feeder links.This paper introduces a new smart gateway diversity combination scheme that combinates N-active(K=2)and N+1 diversity method in detail from the working principle,gateway switching strategy,evaluation of system availability and implementation complexity.In addition,a feeder link outage event prediction algorithm featuring combination scheme is given detailly based on modified time-adaptive linear regression.Compared with the existing N+P scheme,the proposed scheme can provide higher system availability and more stable user’s experience under the condition of properly increasing the complexity of payload design.Compared with Nactive scheme that has been reported,it is much easier to implement in engineering and more cost-effective.As a result,the combination scheme is a realistic solution based on a trade-off between performance improvement and implementation complexity.展开更多
The evaluation of geometric calibration accuracy of high resolution satellite images has been increasingly recognized in recent years.In order to evaluate geometric accuracy for dual-camera satellite images based on t...The evaluation of geometric calibration accuracy of high resolution satellite images has been increasingly recognized in recent years.In order to evaluate geometric accuracy for dual-camera satellite images based on the ground control points(GCP),a rigorous geometric imaging model,which was based on the collinear equation of the probe directional angle and the optimized tri-axial attitude determination(TRIAD)algorithm,is presented.Two reliable test fields in Tianjin and Jinan(China)were utilized for geometric accuracy validation of Pakistan Remote Sensing Satellite-1.The experimental results demonstrate a certain deviation of the on-orbit calibration result from the initial design values of the calibration parameters.Therefore,on-orbit geometric calibration is necessary for optical satellite imagery.Within this research,the geometrical performances including positioning accuracy without/with GCP and band registration of the dual-camera satellite were analyzed in detail,and the results of geometric image quality are assessed and discussed.As a result,it is feasible and necessary to establish such a geometric calibration model to evaluate the geometric quality of dual-camera satellite.展开更多
Over the next decade,Very High-Throughput Satellite (VHTS) will bring enough capacity to serve high speed internet and in-flight connectivity markets at scale,offering fiber-like services both in terms of price and sp...Over the next decade,Very High-Throughput Satellite (VHTS) will bring enough capacity to serve high speed internet and in-flight connectivity markets at scale,offering fiber-like services both in terms of price and speed.In this context,a generic VHTS mission utilizing Q/V-band feeder links and Ka-band user links is described.However,the rain attenuation on the feeder links becomes a limiting issue because of the higher frequencies.Toward this,an exploitation of multiple gateways (GWs) as a transmit diversity measure for overcoming severe propagation effects are being considered.Ground Application System (GAS) design of VHTS is illustrated including N+P GWs (N active and P redundant GWs) diversity,frequency plan,link budget and system capacity.展开更多
By summarizing the history,human achievements in lunar exploration,the vision and prospect of the con-strucion of a lunar base for the further development in lunar exploration is proposed.The idea of building a"b...By summarizing the history,human achievements in lunar exploration,the vision and prospect of the con-strucion of a lunar base for the further development in lunar exploration is proposed.The idea of building a"beehive"lunar vllage is proposed,and the promotion of future lunar exploration along with the impact on the development of science,technology and the economy is analyzed in this paper。展开更多
A new architecture of null steering antenna based upon the technology of space-time adaptive processing（STAP） with optimized parameters is proposed. The new STAP antenna is comprised of multiple channels and each ch...A new architecture of null steering antenna based upon the technology of space-time adaptive processing（STAP） with optimized parameters is proposed. The new STAP antenna is comprised of multiple channels and each channel is a transversal filter. So separate sensor element for the reference signal is not required because the antenna gets the reference signal from the first sensor of the auxiliary array. Furthermore, the least mean square（LMS） algorithm is employed to calculate the weight vector. Detailed analysis about the relationship between noise power and output error is investigated. Compared with the traditional null steering antenna in space or space-time domain, the new approach obtains more freedom degrees and can suppress both the wideband and narrowband interferences more efficiently with deeper nulls. Simulation results shows that the proposed architecture outperforms the conventional STAP techniques for interference suppression.展开更多
This article presents a complete nonlinear controller design for a class of spin-stabilized canard-controlled projectiles.Uniformly ultimate boundedness and tracking are achieved,exploiting a heavily coupled,bounded u...This article presents a complete nonlinear controller design for a class of spin-stabilized canard-controlled projectiles.Uniformly ultimate boundedness and tracking are achieved,exploiting a heavily coupled,bounded uncertain and highly nonlinear model of longitudinal and lateral dynamics.In order to estimate unmeasurable states,an observer is proposed for an augmented multiple-input-multiple-output（MIMO） nonlinear system with an adaptive sliding mode term against the disturbances.Under the frame of a backstepping design,an adaptive sliding mode output-feedback dynamic surface control（DSC） approach is derived recursively by virtue of the estimated states.The DSC technique is adopted to overcome the problem of ‘‘explosion of complexity＂ and relieve the stress of the guidance loop.It is proven that all signals of the MIMO closed-loop system,including the observer and controller,are uniformly ultimately bounded,and the tracking errors converge to an arbitrarily small neighborhood of the origin.Simulation results for the observer and controller are provided to illustrate the feasibility and effectiveness of the proposed approach.展开更多
Satellite Based Augmentation Systems(SBASs)improve the positioning accuracy and integrity by broadcasting to the civil aviation community the corrections and integrity parameters.A snapshot algorithm based on the mini...Satellite Based Augmentation Systems(SBASs)improve the positioning accuracy and integrity by broadcasting to the civil aviation community the corrections and integrity parameters.A snapshot algorithm based on the minimum variance estimation is investigated in this study to calculate the satellite clock and orbit corrections.A chi-square test is performed on the remaining errors in the corrected ephemeris to guarantee the integrity.User Differential Range Error(UDRE)and scaling matrix contained in Message Type 28 are derived using the covariance information based on the assumption that one of the reference stations failed.A software package is developed and applied in the real data collected at 26 stations.International GNSS(Global Navigation Satellite System)Service(IGS)precise clock and orbit products are taken as the references to assess the accuracy of corrections.For both Global Positioning System(GPS)and BeiDou Navigation Satellite System(BDS),the range accuracy of 0.10 m can be achieved with the employment of the derived corrections.No obvious performance difference between GPS and BDS is found.UDREs for all visible satellites are generated with the maximum index of 12 and minimum index of 3.The geometric range differences calculated with IGS precise products and broadcast ephemeris are employed to assess the integrity of UDRE.It is found that the UDRE is able to bound the residuals with 99.9%confidence which meet the requirement of aviation users.With ionospheric delay corrected by Global Ionosphere Map(GIM),the positioning accuracy of 0.98 m with GPS corrections and 0.80 m with multi-constellation augmentation can be achieved which indicates a significant improvement of GPS standalone results.展开更多
Correction to:Satell Navig(2020)1:12 https://doi.org/10.1186/s43020-020-00010-2 In the original publication of this article(Li et al.2020),there are several corrections as below:1.In the first paragraph of this articl...Correction to:Satell Navig(2020)1:12 https://doi.org/10.1186/s43020-020-00010-2 In the original publication of this article(Li et al.2020),there are several corrections as below:1.In the first paragraph of this article,the sentence“In recent years,China has been actively promoting the con-struction and development of the BeiDou Navigation Sat-ellite System(BDS),and by the end of the year 2000 the construction of BDS-1 was complete and BDS-1 began to provide GPS services for China.”should be changed into“In recent years,China has been actively promoting the construction and development of the BeiDou Navigation Satellite System(BDS),and by the end of the year 2000 the construction of BDS-1 was completed and BDS-1 began to provide services for China.”The word“GPS”should be removed.展开更多
Cloud computing provides the capability to con-nect resource-constrained clients with a centralized and shared pool of resources,such as computational power and storage on demand.Large matrix determinant computation i...Cloud computing provides the capability to con-nect resource-constrained clients with a centralized and shared pool of resources,such as computational power and storage on demand.Large matrix determinant computation is almost ubiquitous in computer science and requires large-scale data computation.Currently,techniques for securely outsourcing matrix determinant computations to untrusted servers are of utmost importance,and they have practical value as well as theoretical significance for the scientific community.In this study,we propose a secure outsourcing method for large matrix determinant computation.We em-ploy some transformations for privacy protection based on the original matrix,including permutation and mix-row/mix-column operations,before sending the target matrix to the cloud.The results returned from the cloud need to be de-clypled anul verified U ubtainl te cullett delinall.Il1 comparison with previously proposed algorithms,our new al-gorithm achieves a higher security level with greater cloud ef-ficiency.The experimental results demonstrate the efficiency and effectiveness of our algorithm.展开更多
The rapid decline of Arctic sea ice has been reminding us the significant impacts caused by global warming.However,the other side of the coin is that this opens a window to utilize the Arctic sea routes in the summer ...The rapid decline of Arctic sea ice has been reminding us the significant impacts caused by global warming.However,the other side of the coin is that this opens a window to utilize the Arctic sea routes in the summer seasons,bringing remarkable economic benefits for ocean transportation between Asia and Europe.However,commercial vessels with low ice classes must tackle substantial environmental challenges in the Arctic sea routes,particularly those caused by variable sea ice,even in the melting seasons.Therefore,the science-based support for shipping safety in the Arctic sea routes is being given more prominence.Emerging satellite remote sensing technology plays a critical role in environmental monitoring in the Arctic.This paper reviews state-of-the-art satellite observations on monitoring sea ice and potential applications on supporting shipping activities in the Arctic Ocean.Moreover,we introduced a recently developed system based on satellite observations to support the safe transportation of Chinese cargo vessels in the Arctic northern sea route,demonstrating the efforts by both the science and business communities to promote the development of the polar silk road.展开更多
Retrieval experiment was made for global total column ozone using the first year measurements of Total Ozone Unit (TOU) on board the second generation polar orbiting meteorological satellite of China, FY-3/A. The retr...Retrieval experiment was made for global total column ozone using the first year measurements of Total Ozone Unit (TOU) on board the second generation polar orbiting meteorological satellite of China, FY-3/A. The retrieval results were analyzed and validated by comparison with AURA/OMI, Meteop/GOME-2 global ozone products and ground-based ozone measurement data. The qualititative comparisons over the globe especially over Antarctica and the Tibetan Plateau show that the spatial and temporal distribution characteristics are consistent with OMI and GOME-2 products. The quantitative comparisons with ground-based measurements and AURA/OMI ozone product were made over 74 stations, the TOU total ozone retrieval has a 3% rms relative error compared with AURA/OMI ozone product and 4.2% rms relative error with ground-based measurements. The maximum difference between satellite retrieval and ground-based measurements was found in the Antarctica ozone hole. The TOU global ozone product is operational and distributed to all users.展开更多
Precise Point Positioning(PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with ...Precise Point Positioning(PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with a regional tracking network;therefore, satellite orbits are usually estimated by a global tracking network with a large number of ground stations. However, it is expensive to build globally distributed stations. Fortunately, BeiDou-3 satellites carry an InterSatellite Link(ISL) payload, which can track the whole arc of the BeiDou-3 satellites and enhance the orbit determination accuracy with regional ground stations. In this contribution, a novel orbit determination strategy for BeiDou-3 PPP is proposed, in which the BeiDou-3 satellite orbits are enhanced by the ISL. First, the generation of precise satellite products is demonstrated in detail.In addition, the products are assessed by Satellite Laser Ranging(SLR) residuals and overlap comparisons. Moreover, the products are used for receivers in China's Mainland to carry out the static and kinematic modes to research the PPP performance of Bei Dou-3’s 3IGSO/24MEO constellation.The SLR validations of the satellite orbits demonstrate an accuracy better than 0.1 m in the radial component, and the orbit overlap comparisons show accuracies of 0.016 m in the radial component,0.088 m in the along-track component and 0.087 m in the cross-track component. The Standard Deviation(STD) in the differences in overlapping arcs for the estimated satellite clocks is approximately 0.10 ns. The static PPP results demonstrate that the error in both the horizontal and vertical components is smaller than 10 cm after 30 minutes of convergence. After 24 hours of convergence,the errors are 0.70 cm, 0.63 cm and 1.99 cm for the north, east and up components, respectively.The kinematic PPP experiment illustrates that the Root Mean Square(RMS) position errors in the north, east and up components are approximately 3.23 cm, 5.27 cm and 8.64 cm, respectively,after convergence. The obtainable positioning and convergence performances are comparable to those using products generated by global tracking networks.展开更多
基金the Postdoctoral ScienceFoundation of China(No.2023M730156)the NationalNatural Foundation of China(No.62301012).
文摘Hyper-and multi-spectral image fusion is an important technology to produce hyper-spectral and hyper-resolution images,which always depends on the spectral response function andthe point spread function.However,few works have been payed on the estimation of the two degra-dation functions.To learn the two functions from image pairs to be fused,we propose a Dirichletnetwork,where both functions are properly constrained.Specifically,the spatial response function isconstrained with positivity,while the Dirichlet distribution along with a total variation is imposedon the point spread function.To the best of our knowledge,the neural network and the Dirichlet regularization are exclusively investigated,for the first time,to estimate the degradation functions.Both image degradation and fusion experiments demonstrate the effectiveness and superiority of theproposed Dirichlet network.
基金Chinese National Natural Science Foundation(No.51890881)Science and Technology Project of Hebei Education Department(Nos.ZD2020156,QN2018228).
文摘Because of descriptive nonlinearity and computational inefficiency,topology optimization with fatigue life under aperiodic loads has developed slowly.A fatigue constraint topology optimization method based on bidirectional evolutionary structural optimization(BESO)under an aperiodic load is proposed in this paper.In viewof the severe nonlinearity of fatigue damagewith respect to design variables,effective stress cycles are extracted through transient dynamic analysis.Based on the Miner cumulative damage theory and life requirements,a fatigue constraint is first quantified and then transformed into a stress problem.Then,a normalized termination criterion is proposed by approximatemaximum stress measured by global stress using a P-normaggregation function.Finally,optimization examples show that the proposed algorithm can not only meet the requirements of fatigue life but also obtain a reasonable configuration.
基金supported in part by the National Natural Science Foundation of China (Grant Nos.42074044 and 41974041)in part by “Young Talent Lifting Project” of China Association for Science and Technology (Grant No.2019QNRC001)。
文摘Radio frequency signal compatibility is the basis of interoperability of the Satellite eBased Augmentation System(SBAS).SBAS should abide by relative international radio regulations of International Telecommunication Union(ITU) and meet the compatibility requirements of radio frequency signal between the Global Navigation Satellite System(GNSS)/SBAS,in order to avoid negative mutual interference.According to ITU Proposal and related reference and assumptions,the paper made simulation of signal receiving maximum power in the Bei Dou Satellite-Based Augmentation System(BDSBAS)global signal coverage.And then,interference of BDSBAS to Global Positioning System(GPS)/WAAS(Wide Area Augmentation System) on L1/L5 bands were calculated and analyzed,with equivalent carrierto-noise ratio as the evaluation parameter.The result shows that the carrier-to-noise ratio decrease of GPS/WAAS caused by BDSBAS B1 C and B2 a signals are extremely lower than inter-system interference of GPS/WAAS,and thus can be ignored in practical applications.Therefore,BDSBAS will not cause the service performance degradation of GPS and WAAS.
文摘On-Line Analytical Processing (OLAP) is based on pre-computation of data cubes, which greatly reduces the response time and improves the performance of OLAP. Frag-Shells algorithm is a common method of precomputation.However, it relies too much on the data dispersion that it performs poorly, when confronts large amount of highly disperse data. As the amount of data grows fast nowadays, the efficiency of data cube construction is increasingly becoming a significant bottleneck. In addition, with the popularity of cloud computing and big data, MapReduce framework proposed by Google is playing an increasingly prominent role in parallel processing. It is an intuitive idea that MapReduce framework can be used to enhance the efficiency of parallel data cube construction. In this paper, by improving the Frag-Shells algorithm based on the irrelevance of data dispersion, and taking advantages of the high parallelism of MapReduce framework, we propose an improved Frag-Shells algorithm based on MapReduce framework. The simulation results prove that the proposed algorithm greatly enhances the efficiency of cube construction.
文摘As a means of copyright protection for multimedia data, digital watermarking technology has attracted more and more attention in various research fields. Researchers have begun to explore the feasibility of applying it to remote sensing data recently. Because of the particularity of remote sensing image, higher requirements are put forward for its security and management, especially for the copyright protection, illegal use and authenticity identification of remote sensing image data. Therefore, this paper proposes to use image watermarking technology to achieve comprehensive security protection of remote sensing image data, while the use of cryptography technology increases the applicability and security of watermarking technology. The experimental results show that the scheme of remote sensing image digital watermarking technology has good performance in the imperceptibility and robustness of watermarking.
文摘Multipath and continuous wave (CW) interference may cause severe performance degradation of global navigation satellite system (GNSS) receivers. This paper analyzes the code tracking performance of early-minus-late power (EMLP) discriminator of GNSS receivers in the presence of multipath and CW interference. An analytical expression of the code tracking error is suggested for EMLP discriminator, and it can be used to assess the effect of multipath and CW interference. The derived expression shows that the combined effects include three components: multipath component;CW interference component and the combined component of multipath and CW interference. The effect of these components depends on some factors which can be classified into two categories: the receiving environment and the receiver parameters. Numerical results show how these factors affect the tracking performances. It is shown that the proper receiver parameters can suppress the combined effects of multipath and CW interference.
文摘The electromagnetic satellite Zhangheng 01(ZH-01) was successfully launched on February 2, 2018. The GNSS Radio Occultation(GRO) receiver on board the satellite is able to observe the occultation events of GPS and BeiDou navigation satellites. We analyzed the data acquired during the in-orbit testing period. We concludes that the GRO ionosphere inversion results are reasonable,the trend is correct, the satellite can observe about 600 ionosphere occultation events each day. The global coverage of more than 30000 consecutive GRO events in more than two months were analyzed and compared with COSMIC observations: both the GRO and COSMIC occultation can realize global coverage: the Nm F2 and Hm F2 global distributions are similar and change obviously with latitude. We used three digisondes at different latitudes to analyze and compare the spatio-temporally consistent GRO data: the RMSE of GRO Nm F2 relative to digisonde is better than 9.41%, the correlation coefficient is better than 0.8682: the relative RMSE of Hm F2 is better than 7.80% and the correlation coefficient is better than 0.7066.
文摘China's remote sensing satellite applications started in the 1960s by processing and using foreign satellite data.In the 1990s,China launched its first meteorological satellite,and focused on the construction of Chinese remote sensing satellites and ground application systems.The development of China's remote sensing satellite system focuses
基金supported by the Key Pre-Research Project for Civil Space Technology(No.B0106).
文摘The next generation of High Throughput Satellite(HTS)will exploit Q/V band for the feeder link and Ka band for the user link.The exploitation of multiple gateways(GWs)is a transmit diversity measure to compensate severe rain attenuation of Q/V band feeder links.This paper introduces a new smart gateway diversity combination scheme that combinates N-active(K=2)and N+1 diversity method in detail from the working principle,gateway switching strategy,evaluation of system availability and implementation complexity.In addition,a feeder link outage event prediction algorithm featuring combination scheme is given detailly based on modified time-adaptive linear regression.Compared with the existing N+P scheme,the proposed scheme can provide higher system availability and more stable user’s experience under the condition of properly increasing the complexity of payload design.Compared with Nactive scheme that has been reported,it is much easier to implement in engineering and more cost-effective.As a result,the combination scheme is a realistic solution based on a trade-off between performance improvement and implementation complexity.
基金supported by the National Natural Science Foundation of China(No.41801291)。
文摘The evaluation of geometric calibration accuracy of high resolution satellite images has been increasingly recognized in recent years.In order to evaluate geometric accuracy for dual-camera satellite images based on the ground control points(GCP),a rigorous geometric imaging model,which was based on the collinear equation of the probe directional angle and the optimized tri-axial attitude determination(TRIAD)algorithm,is presented.Two reliable test fields in Tianjin and Jinan(China)were utilized for geometric accuracy validation of Pakistan Remote Sensing Satellite-1.The experimental results demonstrate a certain deviation of the on-orbit calibration result from the initial design values of the calibration parameters.Therefore,on-orbit geometric calibration is necessary for optical satellite imagery.Within this research,the geometrical performances including positioning accuracy without/with GCP and band registration of the dual-camera satellite were analyzed in detail,and the results of geometric image quality are assessed and discussed.As a result,it is feasible and necessary to establish such a geometric calibration model to evaluate the geometric quality of dual-camera satellite.
文摘Over the next decade,Very High-Throughput Satellite (VHTS) will bring enough capacity to serve high speed internet and in-flight connectivity markets at scale,offering fiber-like services both in terms of price and speed.In this context,a generic VHTS mission utilizing Q/V-band feeder links and Ka-band user links is described.However,the rain attenuation on the feeder links becomes a limiting issue because of the higher frequencies.Toward this,an exploitation of multiple gateways (GWs) as a transmit diversity measure for overcoming severe propagation effects are being considered.Ground Application System (GAS) design of VHTS is illustrated including N+P GWs (N active and P redundant GWs) diversity,frequency plan,link budget and system capacity.
文摘By summarizing the history,human achievements in lunar exploration,the vision and prospect of the con-strucion of a lunar base for the further development in lunar exploration is proposed.The idea of building a"beehive"lunar vllage is proposed,and the promotion of future lunar exploration along with the impact on the development of science,technology and the economy is analyzed in this paper。
基金supported by the China Academy of Space Technology (CAST) Fund in 2014 (CAST20140008)the Fundamental Research Funds for the Central University of China (106112013CDJZR160002)
文摘A new architecture of null steering antenna based upon the technology of space-time adaptive processing（STAP） with optimized parameters is proposed. The new STAP antenna is comprised of multiple channels and each channel is a transversal filter. So separate sensor element for the reference signal is not required because the antenna gets the reference signal from the first sensor of the auxiliary array. Furthermore, the least mean square（LMS） algorithm is employed to calculate the weight vector. Detailed analysis about the relationship between noise power and output error is investigated. Compared with the traditional null steering antenna in space or space-time domain, the new approach obtains more freedom degrees and can suppress both the wideband and narrowband interferences more efficiently with deeper nulls. Simulation results shows that the proposed architecture outperforms the conventional STAP techniques for interference suppression.
基金supported by the National Natural Science Foundation of China(No.11532002)
文摘This article presents a complete nonlinear controller design for a class of spin-stabilized canard-controlled projectiles.Uniformly ultimate boundedness and tracking are achieved,exploiting a heavily coupled,bounded uncertain and highly nonlinear model of longitudinal and lateral dynamics.In order to estimate unmeasurable states,an observer is proposed for an augmented multiple-input-multiple-output（MIMO） nonlinear system with an adaptive sliding mode term against the disturbances.Under the frame of a backstepping design,an adaptive sliding mode output-feedback dynamic surface control（DSC） approach is derived recursively by virtue of the estimated states.The DSC technique is adopted to overcome the problem of ‘‘explosion of complexity＂ and relieve the stress of the guidance loop.It is proven that all signals of the MIMO closed-loop system,including the observer and controller,are uniformly ultimately bounded,and the tracking errors converge to an arbitrarily small neighborhood of the origin.Simulation results for the observer and controller are provided to illustrate the feasibility and effectiveness of the proposed approach.
基金the Equipment Pre-research Foundation of China(No.61405180103)the National Natural Science Foundation of China(No.41974041).
文摘Satellite Based Augmentation Systems(SBASs)improve the positioning accuracy and integrity by broadcasting to the civil aviation community the corrections and integrity parameters.A snapshot algorithm based on the minimum variance estimation is investigated in this study to calculate the satellite clock and orbit corrections.A chi-square test is performed on the remaining errors in the corrected ephemeris to guarantee the integrity.User Differential Range Error(UDRE)and scaling matrix contained in Message Type 28 are derived using the covariance information based on the assumption that one of the reference stations failed.A software package is developed and applied in the real data collected at 26 stations.International GNSS(Global Navigation Satellite System)Service(IGS)precise clock and orbit products are taken as the references to assess the accuracy of corrections.For both Global Positioning System(GPS)and BeiDou Navigation Satellite System(BDS),the range accuracy of 0.10 m can be achieved with the employment of the derived corrections.No obvious performance difference between GPS and BDS is found.UDREs for all visible satellites are generated with the maximum index of 12 and minimum index of 3.The geometric range differences calculated with IGS precise products and broadcast ephemeris are employed to assess the integrity of UDRE.It is found that the UDRE is able to bound the residuals with 99.9%confidence which meet the requirement of aviation users.With ionospheric delay corrected by Global Ionosphere Map(GIM),the positioning accuracy of 0.98 m with GPS corrections and 0.80 m with multi-constellation augmentation can be achieved which indicates a significant improvement of GPS standalone results.
文摘Correction to:Satell Navig(2020)1:12 https://doi.org/10.1186/s43020-020-00010-2 In the original publication of this article(Li et al.2020),there are several corrections as below:1.In the first paragraph of this article,the sentence“In recent years,China has been actively promoting the con-struction and development of the BeiDou Navigation Sat-ellite System(BDS),and by the end of the year 2000 the construction of BDS-1 was complete and BDS-1 began to provide GPS services for China.”should be changed into“In recent years,China has been actively promoting the construction and development of the BeiDou Navigation Satellite System(BDS),and by the end of the year 2000 the construction of BDS-1 was completed and BDS-1 began to provide services for China.”The word“GPS”should be removed.
基金supported by the National Natural Science Foundation of China(Grant No.61502269)National Key Research and Development Program of China(2017YFA0303903)Zhejiang Province Key R&D Project(2017C01062).
文摘Cloud computing provides the capability to con-nect resource-constrained clients with a centralized and shared pool of resources,such as computational power and storage on demand.Large matrix determinant computation is almost ubiquitous in computer science and requires large-scale data computation.Currently,techniques for securely outsourcing matrix determinant computations to untrusted servers are of utmost importance,and they have practical value as well as theoretical significance for the scientific community.In this study,we propose a secure outsourcing method for large matrix determinant computation.We em-ploy some transformations for privacy protection based on the original matrix,including permutation and mix-row/mix-column operations,before sending the target matrix to the cloud.The results returned from the cloud need to be de-clypled anul verified U ubtainl te cullett delinall.Il1 comparison with previously proposed algorithms,our new al-gorithm achieves a higher security level with greater cloud ef-ficiency.The experimental results demonstrate the efficiency and effectiveness of our algorithm.
基金supported by the National Science Fund for Distinguished Young Scholars(No.42025605).
文摘The rapid decline of Arctic sea ice has been reminding us the significant impacts caused by global warming.However,the other side of the coin is that this opens a window to utilize the Arctic sea routes in the summer seasons,bringing remarkable economic benefits for ocean transportation between Asia and Europe.However,commercial vessels with low ice classes must tackle substantial environmental challenges in the Arctic sea routes,particularly those caused by variable sea ice,even in the melting seasons.Therefore,the science-based support for shipping safety in the Arctic sea routes is being given more prominence.Emerging satellite remote sensing technology plays a critical role in environmental monitoring in the Arctic.This paper reviews state-of-the-art satellite observations on monitoring sea ice and potential applications on supporting shipping activities in the Arctic Ocean.Moreover,we introduced a recently developed system based on satellite observations to support the safe transportation of Chinese cargo vessels in the Arctic northern sea route,demonstrating the efforts by both the science and business communities to promote the development of the polar silk road.
基金supported by the National High-Tech Research & Development Program of China (2008AA121703)the National Natural Science Foundation of China (40905056)+3 种基金the State Key Labora-tory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC-KF-2008-11)Beijing Urban Meteorology Research Fund (UMRF-200704)the 11th Five-Year Plan of National Science and Technology Key Project (2008BAC34B04-2)the National Basic Research Program of China (2005CB422200x and 2006CB403702)
文摘Retrieval experiment was made for global total column ozone using the first year measurements of Total Ozone Unit (TOU) on board the second generation polar orbiting meteorological satellite of China, FY-3/A. The retrieval results were analyzed and validated by comparison with AURA/OMI, Meteop/GOME-2 global ozone products and ground-based ozone measurement data. The qualititative comparisons over the globe especially over Antarctica and the Tibetan Plateau show that the spatial and temporal distribution characteristics are consistent with OMI and GOME-2 products. The quantitative comparisons with ground-based measurements and AURA/OMI ozone product were made over 74 stations, the TOU total ozone retrieval has a 3% rms relative error compared with AURA/OMI ozone product and 4.2% rms relative error with ground-based measurements. The maximum difference between satellite retrieval and ground-based measurements was found in the Antarctica ozone hole. The TOU global ozone product is operational and distributed to all users.
基金supported by the National Natural Science Foundation of China(No.41804030)。
文摘Precise Point Positioning(PPP) requires precise products, including high-accuracy satellite orbit and clock parameters. It is impossible to obtain an orbit solution that is sufficiently accurate for PPP services with a regional tracking network;therefore, satellite orbits are usually estimated by a global tracking network with a large number of ground stations. However, it is expensive to build globally distributed stations. Fortunately, BeiDou-3 satellites carry an InterSatellite Link(ISL) payload, which can track the whole arc of the BeiDou-3 satellites and enhance the orbit determination accuracy with regional ground stations. In this contribution, a novel orbit determination strategy for BeiDou-3 PPP is proposed, in which the BeiDou-3 satellite orbits are enhanced by the ISL. First, the generation of precise satellite products is demonstrated in detail.In addition, the products are assessed by Satellite Laser Ranging(SLR) residuals and overlap comparisons. Moreover, the products are used for receivers in China's Mainland to carry out the static and kinematic modes to research the PPP performance of Bei Dou-3’s 3IGSO/24MEO constellation.The SLR validations of the satellite orbits demonstrate an accuracy better than 0.1 m in the radial component, and the orbit overlap comparisons show accuracies of 0.016 m in the radial component,0.088 m in the along-track component and 0.087 m in the cross-track component. The Standard Deviation(STD) in the differences in overlapping arcs for the estimated satellite clocks is approximately 0.10 ns. The static PPP results demonstrate that the error in both the horizontal and vertical components is smaller than 10 cm after 30 minutes of convergence. After 24 hours of convergence,the errors are 0.70 cm, 0.63 cm and 1.99 cm for the north, east and up components, respectively.The kinematic PPP experiment illustrates that the Root Mean Square(RMS) position errors in the north, east and up components are approximately 3.23 cm, 5.27 cm and 8.64 cm, respectively,after convergence. The obtainable positioning and convergence performances are comparable to those using products generated by global tracking networks.
