National Key Laboratory of Microwave Imaging Technology

Beijing, China

National Key Laboratory of Microwave Imaging Technology

Beijing, China
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Liu J.,Chinese Academy of Sciences | Liu J.,CAS Institute of Electronics | Hong W.,National Key Laboratory of Microwave Imaging Technology | Hong W.,CAS Institute of Electronics
Journal of Electronics | Year: 2012

Range-Doppler (RD) method and Reverse-Range-Doppler (RRD) method are combined together to achieve automatic geocoding of Synthetic Aperture Radar (SAR) image quickly and accurately in the paper. The RD method is firstly used to locate the four corners of the image, then the other pixels of the image can be located by Reverse-Range-Doppler (RRD) method. Resampling is performed at last. The approach has an advantage over previous techniques in that it does not require ground control points and is independent of spacecraft attitude knowledge or control. It can compensate the shift due to the assumed Doppler frequency in SAR image preprocessing. RRD simplifies the process of RD, therefore speeds up the computation. The experimental results show that a SAR image can be automated geocoded in 30 s using the single CPU (3 GHz) with 1 G memory and an accuracy of 10 m is attainable with this method. © 2012 Science Press, Institute of Electronics, CAS and Springer-Verlag Berlin Heidelberg.


Tan H.,CAS Institute of Electronics | Tan H.,University of Chinese Academy of Sciences | Tan H.,Chinese Academy of Sciences | Hong J.,CAS Institute of Electronics | And 2 more authors.
IEEE Geoscience and Remote Sensing Letters | Year: 2015

A compact polarimetric (CP) synthetic aperture radar (SAR) has an advantage of reconstructing quad-polarimetric (quad-pol) information from measured dual-polarized scattering vectors. In order to fully explore CP data, calibration of CP measurements is important. However, among different system errors, the crosstalk on transmit is not possible to be corrected in measured scattering vectors even when it is already estimated and known. Except scattering vectors, reconstructed quad-pol data are widely used. Three reconstruction algorithms have been published in the literature: one by Souyris et al., a refined algorithm by Nord, and another refined one by Collins et al. However, the removal of transmit crosstalk is still left unresolved. In this letter, we proposed a calibration algorithm to correct the transmit crosstalk in reconstructions of quad-pol data from CP data. We conducted simulations with fully polarimetric Advanced Land Observing Satellite Phased Array L-band SAR data. Simulation results confirmed that the algorithm performed effectively and stably under certain conditions. © 2015 IEEE.


Hua B.,CAS Institute of Electronics | Hua B.,University of Chinese Academy of Sciences | Hua B.,National Key Laboratory of Microwave Imaging Technology | Qi H.,CAS Institute of Electronics | And 4 more authors.
Advances in Space Research | Year: 2010

Spaceborne SAR involves the storage and transmission of large-size sampling data. Block adaptive quantization (BAQ) is now the most widely used onboard data compression algorithm due to its good tradeoff between system performance and complexity. However, when spaceborne SAR raw data is saturated, the performance of conventional BAQ deteriorates dramatically because its precondition of Gaussian distribution of raw data no longer holds. In order to solve this problem, an improved vector quantization (VQ) algorithm is proposed. This algorithm firstly introduces saturation modification to a conventional vector quantizer, obtains the saturation codebook based on Gaussian density function, and then obtains the new vector quantizer for the whole set of Saturation Degree (SD). This algorithm makes the vector quantizer match statistical model of data for the whole set of SD, so the performance of the compression is improved. The case of the 2D signal is explicitly computed. The performance of the proposed algorithm is verified by simulated and real data experiments. © 2010 COSPAR.


Liu J.,Chinese Academy of Sciences | Liu J.,CAS Institute of Electronics | Liu J.,University of Chinese Academy of Sciences | You H.,Chinese Academy of Sciences | And 3 more authors.
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2013

A modified orbit algorithm with sparse ground control points (only three points) for high accuracy geo-rectification of space-borne SAR image is proposed, which is based on range-doppler position model and high precision orbit data of GPS. The algorithm decreases the number of ground control points through simplifying the orbit parameter model, so it can improve the work efficiency on the basic of high accuracy correction.


Ming F.,CAS Institute of Electronics | Ming F.,National Key Laboratory of Microwave Imaging Technology | Hong J.,CAS Institute of Electronics | Hong J.,National Key Laboratory of Microwave Imaging Technology
2011 3rd International Asia-Pacific Conference on Synthetic Aperture Radar, APSAR 2011 | Year: 2011

SAR calibration is one of the most important technique of measurable observation and to calibrate SAR images to normalized radar cross sections (NRCS) a calibration constant is required. Usually the calibration constant is determined by analyzing measurements of corner reflectors or transponders. However, for Global Monitoring mode of ASAR, we can not facture so large radar cross section (RCS) calibrators to satisfy the signal clutter ratio (SCR) of measurement. So we put forward a method to measure the calibration constant based on knowledge of the dependency of the NRCS on the ocean surface wind, which is described by the C-band model CMOD4. We validate our method using real data of ASAR mode. © 2011 KIEES.


Li L.-C.,National Key Laboratory of Microwave Imaging Technology | Li L.-C.,CAS Institute of Electronics | Li L.-C.,University of Chinese Academy of Sciences | Li D.-J.,National Key Laboratory of Microwave Imaging Technology | Li D.-J.,CAS Institute of Electronics
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology | Year: 2014

In this paper a sparse array SAR 3D imaging for continuous scene based on Compressed Sensing (CS) is proposed. It exploits the sparsity property of the SAR image under multi-aperture observation structure which supposes that SAR images become sparse in the transform domain by eliminating the random phase of each scattering cell, and CS theory is introduced into the signal processing in the transform domain. The proposed method can achieve high resolution 3D imaging and get nearly the same image quality as the full array with a few samplings. The proposed method decreases the constrain of the array designing on elevation direction and provides the possibility for imaging in the situation that a full equivalent array cannot be achieved. Simulation results verify the effectiveness of the proposed method.


Xing K.,CAS Institute of Electronics | Xing K.,National Key Laboratory of Microwave Imaging Technology | Deng Y.-K.,CAS Institute of Electronics | Qi H.-M.,CAS Institute of Electronics | Qi H.-M.,National Key Laboratory of Microwave Imaging Technology
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology | Year: 2010

At present, the effective way to resolve the contradiction between huge space-borne SAR raw data rate and limited on-board data-transmission bandwidth is space-borne SAR raw data compression. The higher compression ratio is, the lower data rate will be, but larger quantization error will affect the velocity measurement accuracy of SAR-GMTI. The lower compression ratio is, the less effect of data compression on velocity measurement accuracy is, but the higher data rate will be. Therefore, the choice of data compression ratio needs achieve a compromise between data rate and velocity measurement accuracy. This paper establishes the echo simulation model of space-borne SAR/GMTI system and simulates the raw data of space-borne SAR-GMTI. For Displaced Phase Center Antenna (DPCA) and Along-Track Interferometry (ATI) methods which have significant application potentialities in practice, this paper analyzes the effect of Block Adaptive Quantization (BAQ) algorithm on velocity measurement accuracy in detail. The results of this paper provides important theory basis for the choice of compression ratio of the space-borne SAR/GMTI system.


Liu X.-M.,CAS Institute of Electronics | Liu X.-M.,University of Chinese Academy of Sciences | Gao W.-J.,CAS Institute of Electronics | Gao W.-J.,National Key Laboratory of Microwave Imaging Technology | And 2 more authors.
2010 9th International Symposium on Antennas Propagation and EM Theory, ISAPE 2010 | Year: 2010

An integrated beam synthesis algorithm is presented to optimize the multiple beams of variable look-angle SAR antenna. With an iterative solution scheme of improved projection matrix algorithm, the amplitude excitations (common to all beams) and the phase of such excitations (corresponding to each radiated beam) are determined simultaneously. Antenna beams are controlled by phase only in SAR system. The sample application of multiple beams SAR antenna design is given to illustrate the effectiveness of the presented algorithm. And the noise-equivalent sigma-zero ( NEσ0 ) of SAR system is improved as well. ©2010 IEEE.


Yin J.-F.,National Key Laboratory of Microwave Imaging Technology | Yin J.-F.,CAS Institute of Electronics | Yin J.-F.,University of Chinese Academy of Sciences | Li D.-J.,National Key Laboratory of Microwave Imaging Technology | And 3 more authors.
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology | Year: 2010

In the case of clutter, conventional multi-channel SAR (Synthetic Aperture Radar) executes moving target detection immediately after clutter cancellation, and the influence of range migration is ignored. However, this approach may lose some fast target. The target that not so fast can be detected, but the estimated velocity may be ambiguous, and target accurate location becomes even difficult. So three-frequency three-aperture SAR is presented in this paper to remove the Doppler ambiguity of fast target after clutter suppression. Dual Frequency Conjugated Processing (DFCP) and Keystone transform are employed to remove the Doppler ambiguity and correct range migration of moving target. Thus the Signal Noise Ratio (SNR) can be improved, and then target detection, velocity estimation and location without ambiguity can be completed. The proposed method can achieve the same location accuracy with the existing method as well as increase greatly the velocity range of fast target that can be detected and located. The simulation results show the effectiveness of proposed method.


Zhang Y.,University of Chinese Academy of Sciences | Zhang Y.,CAS Institute of Electronics | Zhang Y.,Chinese Academy of Sciences | Ding C.,CAS Institute of Electronics | And 6 more authors.
Journal of Infrared, Millimeter, and Terahertz Waves | Year: 2012

With the development of several High Resolution (HR) Synthetic Aperture Radar (SAR) systems, many special phenomena appear in the SAR image, especially for the SAR image with millimeter wave. We firmly believed that every detail in the SAR image should have its own special mechanisms and these details may provide some key clues for us to build up the frame work on understanding the SAR image. The synthetic aperture is one of the important particularities about SAR, and the radar is moving during the data is collected, which leads many special phenomena in the SAR image; one of these is the shadow with blurred boundary. In this work, the effect on the shadow region in the SAR image by synthetic aperture is expanded on. The blurred boundary of the shadow is analyzed using imaging formation theory, and the Quadratic Phase Errors (QPE) brought by the synthetic aperture progress is deduced for the first time, which builds up the relationship between the parameters of the shadow caster and the behavior of the shadow in the SAR image. It is found that the QPE is approximately a linear function of the height of the shadow caster. Furthermore, an approach for shadow enhancement based on height variant phase compensation is proposed and it could provide a better effect on shadow enhancement than the traditional technique called Fixed Focus Shadow Enhancement (FFSE), which is proved by theoretical analysis and experiments. Based on the analysis, some typical application of the about the shadow region. It is expected that the work in this paper could be some helpful for the SAR image understanding and the microwave imaging with high resolution. shadow in SAR image is designed and some mini-SAR image with Ku-band is analyzed about the shadow region. It is expected that the work in this paper could be some helpful for the SAR image understanding and the microwave imaging with high resolution. © Springer Science+Business Media, LLC 2012.

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