Time filter

Source Type

Du Y.,Qian Xuesen Laboratory of Space Technology
Lecture Notes in Electrical Engineering | Year: 2015

Six X-ray pulsars (PSR J0218+4232, PSR J0437-4715, PSR B0531-21, PSR J1939+2134, PSR J1024-0719 and PSR J0751+1807) are selected for the mission of deep-space autonomous navigation, and the relevant parameters (including position, proper motion, period and period derivative, etc.) are also listed. Based on the XMM-Newton X-ray timing data and the radio ephemeris for the young pulsar PSR B1509-58, we adopted both absolute timing and relative timing methods to fold its pulse profile in the 0.2–12 keV band. In addition, for the sake of both pulsar-based deep-space autonomous navigation and scientific research, we take the Crab pulsar as an example to fit its X-ray (0.2–30 keV band) spectrum, and obtain its power-law fitted spectrum. Then we estimate the navigation accuracy of the detectors with different effective areas. Finally, we discuss a preliminary probe design principle of X-ray detectors for the pulsar navigation, and give the rough estimations on the effective area and sensitivity. © Springer-Verlag Berlin Heidelberg 2015. Source

Bo L.,Qian Xuesen Laboratory of Space Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Spaceborne Synthetic Aperture Radar (SAR), with "all weather", day or night imaging capabilities, has been playing an important role in the domination of Earth observation. Spaceborne high-resolution wide-swath SAR (HRWS-SAR) can quickly obtain wide range of the earth's surface information, which is of great significance to Earth mapping, geological exploration, vegetation and biomass estimates, marine monitoring, target search, disaster relief, etc. As a result, spaceborne HRWS-SAR has been gaining more and more attention. However, considering the restrictions on pulse repetition frequency (PRF) and power-aperture product, space-based SAR imaging cannot achieve high resolution and wide swath at the same time. Currently existing solutions mainly focus on the antenna system hardware devices, such as MIMO, DBF; other signal-processing-bias solutions, such as Mosaic imaging technology, have higher requirements of the antenna pointing or beam control. These methods adopt more antenna elements or complex beam control method, which greatly increased the demand for hardware performance, and the signal processing method become more complicated as well. In order to relieve the pressure on the system hardware devices, this paper presents a new orthogonal coded waveform method based on the theory of communication. By using this method, the LFM signal is coded by the orthogonal codes to make the neighboring pulses irrelevant, which ensures the azimuth sampling rate as well as a wide swath. Theoretically, this method can alleviate the contradiction between PRF and high resolution wide swath imaging. © 2014 SPIE. Source

Zhang X.,Qian Xuesen Laboratory of Space Technology | Zhang X.,University of Electronic Science and Technology of China | Liu B.,Qian Xuesen Laboratory of Space Technology
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2016

Suffering from ambiguous estimation or heavy computation complexity load, the radial velocity estimation of moving targets becomes the bottleneck of the synthetic aperture radar-ground moving target indication system. In order to improve the radial velocity estimation efficiency, we have proposed an efficient Radon transform (RT) estimation (ERTE) method by using the never exploited geometry information, which performs well in high SNR scenarios but bad for low SNR. Focusing on these, we propose the least square RT estimation (LSRTE) method to improve the estimation accuracy by utilizing the geometry information of multiple RT results. Given the geometry information determining measurement error, we modified the LSRTE into a weighted LSRTE (WLSRTE) method to improve the estimation robustness and accuracy. Experiments results validate the effectiveness of the proposed methods, and the proposed methods perform much more accurate and efficient than the conventional method. © 2016 IEEE. Source

Shi Y.,Qian Xuesen Laboratory of Space Technology | Liang B.,Harbin Institute of Technology | Xu W.,Harbin Institute of Technology | Wang X.,Harbin Institute of Technology
Jiqiren/Robot | Year: 2013

For the problem of trajectory tracking control of free-floating space robot in inertial space, the existing solutions just achieve asymptotical stability, and the transient performance of the system isn't analyzed. To solve this problem, a kind of adaptive backstepping neural network control law based on error transformation is proposed. The constrained outputs are transformed into unconstrained control variables, and then an adaptive backstepping neural network control law is designed to realize unconstrained variable stable control with uncertain dynamic and kinematic parameters. The proposed control algorithm can not only guarantee the globally asymptotical convergence of the trajectory tracking errors in task space, it can also provide additional ensure for the prescribed transient tracking performance of the closed-loop system. The system tracking performance is improved significantly. Finally, numerical simulation is conducted to prove the feasibility and effectiveness of the proposed control strategy. Source

Li H.,Qian Xuesen Laboratory of Space Technology | Man Y.,Qian Xuesen Laboratory of Space Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The image phase coherences (PCs) remain invariant when brightness and contrast changes. A new method of remote sensing image registration is proposed. PCs are firstly extracted from the reference image and the input image. In order to improve the registration efficiency, in the first step the PCs are firstly down-sampled using Gaussian pyramid method, and the coarse translation parameters are calculated using phase correlation. In the second step, Harris corners are detected from the two images, and normalized cross-correlation (NCC) function based on PCs is used to find the corresponding matching corners of the two images, and then obtain parameters of an alignment transform model. Experiments have demonstrated that the coarse-to-fine method can be successfully applied to multi-source images registration. © 2015 SPIE. Source

Discover hidden collaborations