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He L.,Hohai University | He L.,State Key Laboratory of Geo information Engineering | Zhou H.,China Electronics Technology Group Corporation | Zhang G.,China Shipbuilding Industry Corporation
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2017

With the goal of reducing dependence on ground tracking systems, satellite autonomous navigation technologies are developed quickly in the recent several decades. However, precise orbit determination at high orbital altitudes is an important and challenging problem. In this paper, the nonlinear real-time orbit determination problem is investigated. Combined with satellite dynamical model, extended Kalman filter is explored to estimate satellite orbit parameters. Further, considering errors occur in linearization processing, two improvements for the extended Kalman filter algorithm, i.e. extended Kalman filter-I and extended Kalman filter-II, are proposed based on Lagrange's mean value theorem, and respectively focus on choosing better linear expansion point and Jacobian matrix calculation point. Extensive simulations show that extended Kalman filter-I and extended Kalman filter-II significantly enhance orbit accuracy, compared with extended Kalman filter. And the increases in calculation complexity are acceptable. Finally, the robustness of extended Kalman filter-I and extended Kalman filter-II is analyzed by given different initial position errors, and results show that extended Kalman filter-I and extended Kalman filter-II have better robustness than extended Kalman filter. © Institution of Mechanical Engineers.

Sheng L.,CAS Xi'an Institute of Optics and Precision Mechanic | Sheng L.,State Key Laboratory of Geo Information Engineering | Zhao B.,CAS Xi'an Institute of Optics and Precision Mechanic | Qiang P.,CAS Xi'an Institute of Optics and Precision Mechanic | Liu D.,CAS Xi'an Institute of Optics and Precision Mechanic
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

X-ray grazing incidence optics are widely used in X-ray astronomy, especially for imaging payloads Wolter optics are the most workhorse. However, as there are two cascaded mirrors in Wolter type, the efficiency is quite low after two reflections. In this paper a kind of nested conical concentrator is developed with only one reflection to concentrate the X-ray photons and obtain the timing information. The mirror length is 200mm, the mirror foils cover from 38.8 to 100mm in diameter. D263T glass of 0.3mm thickness is used as mirror substrate with Iridium film deposited in order to improve the X-ray reflection. The D263T glass is slumped at 580°C with precisely machined and polished mold. 3D printed resin serves as upper mold for glass cutting. The quality of mirror substrate is mainly determined by the surface of forming mandrel. As the surface roughness is quite important for X-ray reflection, after deposition it is tested with interferometer and AFM, and the roughness is 0.6nm. Mirror integration based on visible light is built, and the conical mirrors are assembled and adjusted by real time monitoring for the focal point of visible light. With the monochromic X-ray source, the concentrator efficiency is tested as 38%@1.49keV, 20%@4.51keV. The focal point is Φ8.2mm in Xray, with 80% of its energy encircled in a 4mm width. This kind of X-ray concentrator could be used in X-ray navigation, X-ray communication and other X-ray timing astronomy. © 2017 SPIE.

He L.,Hohai University | He L.,State Key Laboratory of Geo Information Engineering | Zhou H.,The 28th Institute of CETC
Telecommunication Systems | Year: 2017

TCP has been extensively credited for the stability of the Internet. However, as the product of bandwidth and latency increases, TCP becomes inefficient and prone to instability. The explicit control protocol (XCP) is a promising congestion control protocol that outperforms TCP in terms of efficiency, fairness, convergence speed, persistent queue length and packet loss rate. However, XCP is not globally stable in the presence of heterogeneous delays. When the ratio of maximum to average transmission latency is sufficiently large, XCP will become instability. In this paper, according to the robust control theory, with the help of a recently developed Lyapunov–Krasovskii functional, an improved version of XCP, named R-XCP, is proposed to solve the weakness of XCP under heterogeneous delays, which adjusts parameter (Formula presented.) from an initial value of 0.4 to a reasonable value for improving system robustness. And then, the synthesis problem is reduced to a convex optimization scheme expressed in terms of linear matrix inequalities. Extensive simulations have shown that R-XCP significantly decreases the volatilities of the aggregate traffic rate and control time interval, and indeed achieves this stability goal. Compared with previous work, R-XCP has a better balance between robustness and responsiveness, and the computational complexity declines significantly at the same time. Besides, R-XCP makes the system less sensitive to flows, which contribute little traffic but maliciously report their transmission delays. © 2017 Springer Science+Business Media New York

Miao Q.,Xidian University | Xu P.,Xidian University | Liu T.,Xidian University | Yang Y.,Xi'an Jiaotong University | And 3 more authors.
IEEE Transactions on Image Processing | Year: 2013

Linear features are difficult to be separated from complicated background in color scanned topographic maps, especially when the color of linear features approximate to that of background in some particular images. This paper presents a method, which is based on energy density and the shear transform, for the separation of lines from background. First, the shear transform, which could add the directional characteristics of the lines, is introduced to overcome the disadvantage that linear information loss would happen if the separation method is used in an image, which is in only one direction. Then templates in the horizontal and vertical directions are built to separate lines from background on account of the fact that the energy concentration of the lines usually reaches a higher level than that of the background in the negtive image. Furthermore, the remaining grid background can be wiped off by grid templates matching. The isolated patches, which include only one pixel or less than ten pixels, are removed according to the connected region area measurement. Finally, using the union operation, the linear features obtained in different sheared images could supplement each other, thus the lines of the final result are more complete. The basic property of this method is introducing the energy density instead of color information commonly used in traditional methods. The experiment results indicate that the proposed method could distinguish the linear features from the background more effectively, and obtain good results for its ability in changing the directions of the lines with the shear transform. © 1992-2012 IEEE.

Yang Y.,State Key Laboratory of Geo information Engineering | Yang Y.,Xian Research Institute of Surveying and Mapping | Yang Y.,Beijing Satellite Navigation Center | Xu J.,Beijing Satellite Navigation Center
Geodesy and Geodynamics | Year: 2016

Integrity is significant for safety-of-life applications. Receiver autonomous integrity monitoring (RAIM) has been developed to provide integrity service for civil aviation. At first, the conventional RAIM algorithm is only suitable for single fault detection, single GNSS constellation. However, multiple satellite failure should be considered when more than one satellite navigation system are adopted. To detect and exclude multi-fault, most current algorithms perform an iteration procedure considering all possible fault model which lead to heavy computation burden. An alternative RAIM is presented in this paper based on multiple satellite constellations (for example, GPS and BeiDou (BDS) etc.) and robust estimation for multi-fault detection and exclusion, which can not only detect multi-failures, but also control the influences of near failure observation. Besides, the RAIM algorithm based on robust estimation is more efficient than the current RAIM algorithm for multiple constellation and multiple faults. Finally, the algorithm is tested by GPS/BeiDou data. © 2016 Institute of Seismology, China Earthquake Administration.

Yu S.,Shanxi University | Xu T.,State Key Laboratory of Geo Information Engineering | Xu T.,Xian Research Institute of Surveying and Mapping
Lecture Notes in Electrical Engineering | Year: 2016

This paper evaluates the precision of iGMAS orbit and clock products, and analyzes their consistency. By the methods of orbit comparisons and day boundary discontinuities (DBDs), the iGMAS orbit precision is evaluated. The twice difference method is used to evaluate clock precision. On the basis of precision analysis, consistency of orbit and clock products from different analysis centers (AC) was compared by precise point positioning (PPP) technique. The quality of orbit, clock, and GNSS observation would have a large impact on the accuracy of PPP. Therefore, the experimental data for consistency analysis includes MGEX station observation data with good quality, and the orbit/clock products with comparable precision. Using the proposed method, precision, and consistency of iGMAS orbit and clock products from different AC are analyzed. © Springer Science+Business Media Singapore 2016.

Qian F.,State Key Laboratory of Geo Information Engineering | Wei L.,Xian Research Institute of Surveying and Mapping
Proceedings - 2013 7th International Conference on Image and Graphics, ICIG 2013 | Year: 2013

An optimized occlusion detection method for true orthophoto make is proposed in this paper, aimed at solving the occlusion and shadow problems caused by rectification using digital surface model (DSM). This method draws lessons from sweep way of angle-based detection method and idea of radial tracing detection method. It adds three judge rules to the occlusion detection process to increase its executing efficiency. Using neighbor image's best corresponding pixels can compensate the occlusion area. © 2013 IEEE.

Lv S.,CAS Changchun Institute of Optics and Fine Mechanics and Physics | Lv S.,State Key Laboratory of Geo information Engineering | Liu J.,CAS Changchun Institute of Optics and Fine Mechanics and Physics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

This paper describes the design and realization of a refocusing system for a space TDICCD camera of 2.2-meter focal length, which, features a three mirror anastigmatic(TMA) optical system along with 8 TDICCDs assemble at the focal plane, is high resolution and wide field of view. TDICCDs assemble is a kind of major method of acquiring wide field of view for space camera. In this way, the swath width reach 60km. First, the design of TMA optical system and its advantage of this space TDICCD camera was introduced; Then, the refocusing system as well as the technique of mechanical interleaving assemble for TDICCDs focal plane of this space camera was discussed in detail, At last, the refocusing system was measured. Experimental results indicated that the precision of the refocusing system is ± 3.12μm(3σ), which satisfy the refocusing control system requirements of higher precision and stabilization. © 2015 SPIE.

Lv S.,CAS Changchun Institute of Optics and Fine Mechanics and Physics | Lv S.,State Key Laboratory of Geo information Engineering | Liu J.,CAS Changchun Institute of Optics and Fine Mechanics and Physics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

As a key technology to improve the imaging quality of remote multispectral CCD camera, the performance of a focusing system for multispectral CCD camera was presented in detail in this paper. Firstly, the focusing precision required was calculated in the optical system. The method of direct adjusting multispectral CCD focal plane was proposed, which was suitable for this multispectral CCD camera optical system. Secondly, we developed a focusing system which has the advantages of lower constructional complexity, easier hardware implementation and high focusing sensitivity. Finally, experimental test was constructed to evaluate the focusing precision performance of the focusing system. The result of focusing precision test is 3.62μm(3σ) in a focusing range of ±2.5mm. The experimental result shows that the focusing system we proposed is reasonable, and reliability as well as stable, which meet the focusing precision requirements for multispectral CCD camera. © 2015 SPIE.

Ruan R.,Xian Research Institute of Surveying and Mapping | Ruan R.,State Key Laboratory of Geo information Engineering
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2015

Ambiguity resolution plays an essential role in global GPS/GNSS network solution. In order to fix as many double-difference(DD) ambiguities to the nearest integers as possible, a set of “most-easy-to-fix” independent DD-ambiguities has to be defined. The most usable state-of-art method (the “traditional” method)at present is to make the independency checking on two levels firstly on the baseline level and then the network level, in which the DD-ambiguity candidates are sorted by their fixing probabilities on both levels. Considering the fact that, in general global network solution, the number of stations involved is usually times larger than that of satellites, a new approach for independent DD-ambiguities selection was presented, which makes the independency checking in an analogous two-level way firstly on the constellation level and then the network level. Together with a new procedure for sequential ambiguity fixing based on updating the upper triangular square root of covariance matrix, the new approach is implemented in the satellite positioning and orbit determination system (SPODS) software which is designed and developed at Xi'an Research Institute of Surveying & Mapping. Validation experiment with GPS observation data collected from about 64 IGS stations was carried out, which demonstrate that 1D RMSs for daily orbit solution, compared with IGS final combined solution, are about 0.012 m, and about 92% of DD-ambiguities were fixed, with only neglectable tiny difference tetween the new and traditional method. Another experiment with varied number of stations indicates that the ratio of the number of DD-ambiguities candidates to be checked for independency on the network level between the new and the traditional approach is nearly equal to the ratio of satellites to stations involved. For the cases that more stations are involved than satellites, which are common in actual GPS/GNSS network solution, the computation time for independent DD-ambiguities selection is reduced with the new approach, the more stations involved, the greater advantage is exhibited. ©, 2015, SinoMaps Press. All right reserved.

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