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Zhang F.-B.,Science and Technology on Microwave Imaging Laboratory | Zhang F.-B.,CAS Institute of Electronics | Zhang F.-B.,University of Chinese Academy of Sciences | Liang X.-D.,Science and Technology on Microwave Imaging Laboratory | And 3 more authors.
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology | Year: 2015

Multi-channel SAR can reconstruct the 3-D surface of the observed scene with its resolution power in the elevation. However, with limited baseline length, most methods suffer from limited precision and significant miss rates. In view of this situation, a new 3-D reconstruction method using terrain stagnation point based division is proposed. Firstly, 3-D distribution is obtained using tomography; secondly, stagnation point position and division are conducted to separate the layover; then 3-D reconstruction is conducted using interferometry. This method combines the resolving power of multi-channel SAR and high precision of interferometry. Therefore, reconstruction results with higher precision and greater stability are achieved. The effectiveness of the method is validated using experiments with simulated data. ©, 2015, Science Press. All right reserved. Source


Wang J.,Science and Technology on Microwave Imaging Laboratory | Wang J.,CAS Institute of Electronics | Wang J.,University of Chinese Academy of Sciences | Liang X.D.,Science and Technology on Microwave Imaging Laboratory | And 9 more authors.
Science China Information Sciences | Year: 2014

Special attention has been devoted to multi-input multi-output (MIMO) synthetic aperture radar (SAR) systems in recent years. The applications of MIMO SAR systems which involve 3D imaging, highresolution wide-swath remote sensing, and multi-baseline interferometry are seriously limited to the orthogonal waveforms. Although orthogonal frequency division multiplexing (OFDM) chirp waveforms can be used for MIMO SAR systems to avoid intra-pulse interferences, there is a small frequency shift between the transmitted OFDM pulses. This vulnerable shift, which can not only affect the waveform orthogonality, but also introduce residual phase error, renders the OFDM waveforms impractical. In this paper, an improved OFDM chirp waveform which works without the mentioned shift is presented, along with the novel modulation and efficient demodulation procedures. Comparison between the improved and the conventional OFDM chirp waveforms is detailed. The influence of random noise, quantization error, and Doppler shift on the orthogonality of OFDM waveform is also investigated in this paper. Theoretical analysis and simulation results illustrate the feasibility of this waveform scheme. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg. Source


Li L.,CAS Institute of Electronics | Li L.,Science and Technology on Microwave Imaging Laboratory | Li L.,University of Chinese Academy of Sciences | Hong J.,CAS Institute of Electronics | And 5 more authors.
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology | Year: 2014

The Medium-Earth-Orbit SAR (MEOSAR) is one of the potential next-generation spaceborne SARs. Ionospheric effects analysis is one of the critical techniques for the development of MEOSAR. An analysis model for background ionospheric effect on MEOSAR is established based on the system characteristics of MEOSAR and the spatio-temporal variability of ionosphere. The degradation of image quality, including resolution and displacement distortion, induced by background ionosphere and its spatio-temporal variability is analyzed. The analysis result shows that ionosphere and its time-space variability affect critically the quality of obtained images. In condition of the same ionosphere, the degradation of resolution in both azimuth and range, the distortion on range image and the displacements in azimuth image are all more serious with the increasing of SAR orbit height when the resolution is same. Source


Li L.,CAS Institute of Electronics | Li L.,Science and Technology on Microwave Imaging Laboratory | Li L.,University of Chinese Academy of Sciences | Hong J.,CAS Institute of Electronics | Hong J.,Science and Technology on Microwave Imaging Laboratory
Progress In Electromagnetics Research M | Year: 2013

The Medium-Earth-Orbit SAR (MEOSAR) is one of the most potential next-generation spaceborne SARs for its excellent performances. However, the MEOSAR may not be able to produce data useful for science applications due to ionospheric effects. So it is very necessary to study ionospheric effects for the development of MEOSAR. In this paper, we present ionospheric effects on azimuth imaging for MEOSAR. First, we established an analysis model for ionospheric effects on azimuth imaging of MEOSAR based on the system characteristics of MEOSAR and the temporal-variability of ionosphere. Then, based on the analysis model, we analyzed the effects caused by the quadratic and cubic phase errors induced by temporal-variability of ionosphere on azimuth imaging. According to the results of our analysis, we conclude that both the quadratic phase error and the cubic phase error neglected for Low-Earth-Orbit SAR (LEOSAR) will deteriorate the azimuth imaging for MEOSAR. Furthermore, ionospheric effects will become more and more serious with the increase of SAR altitude and the improvement of azimuth resolution designed. Source


Zhang B.C.,Science and Technology on Microwave Imaging Laboratory | Zhang B.C.,CAS Institute of Electronics | Hong W.,Science and Technology on Microwave Imaging Laboratory | Hong W.,CAS Institute of Electronics | And 2 more authors.
Science China Information Sciences | Year: 2012

This paper provides principles and applications of the sparse microwave imaging theory and technology. Synthetic aperture radar (SAR) is an important method of modern remote sensing. During decades microwave imaging technology has achieved remarkable progress in the system performance of microwave imaging technology, and at the same time encountered increasing complexity in system implementation. The sparse microwave imaging introduces the sparse signal processing theory to radar imaging to obtain new theory, new system and new methodology of microwave imaging. Based on classical SAR imaging model and fundamental theories of sparse signal processing, we can derive the model of sparse microwave imaging, which is a sparse measurement and recovery problem and can be solved with various algorithms. There exist several fundamental points that must be considered in the efforts of applying sparse signal processing to radar imaging, including sparse representation, measurement matrix construction, unambiguity reconstruction and performance evaluation. Based on these considerations, the sparse signal processing could be successfully applied to radar imaging, and achieve benefits in several aspects, including improvement of image quality, reduction of data amount for sparse scene and enhancement of system performance. The sparse signal processing has also been applied in several specific radar imaging applications. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg. Source

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