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Editor Work2012 Vol. 1, No. 2
Previous Issue
2012, 1(2): 109-123.
Abstract
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Starting from the detection principle and characteristics of passive radar, this paper describes the development of passive radar based on the low frequency band (HF/VHF/UHF) digital broadcasting and TV signal. Based on the radio coverage ratio and technical features of digital broadcasting and TV signals, the research status in abroad, especially in Europe, is introduced at first, on experimental systems, technical parameters, and comparative experiments. Then the latest development of passive radars, in different frequency bands in China, both theory and experimental study are presented. Followed is the commentary on the key techniques and problems of Digital Broadcasting-based Passive Radar (DBPR), including the waveforms properties and its modification, reference signal extraction, multipath clutter rejection, target detection, tracking, and fusion as well as real-time signal processing. Finally, the prospects of development and application of this kind of passive radar are discussed.
Starting from the detection principle and characteristics of passive radar, this paper describes the development of passive radar based on the low frequency band (HF/VHF/UHF) digital broadcasting and TV signal. Based on the radio coverage ratio and technical features of digital broadcasting and TV signals, the research status in abroad, especially in Europe, is introduced at first, on experimental systems, technical parameters, and comparative experiments. Then the latest development of passive radars, in different frequency bands in China, both theory and experimental study are presented. Followed is the commentary on the key techniques and problems of Digital Broadcasting-based Passive Radar (DBPR), including the waveforms properties and its modification, reference signal extraction, multipath clutter rejection, target detection, tracking, and fusion as well as real-time signal processing. Finally, the prospects of development and application of this kind of passive radar are discussed.
2012, 1(2): 124-135.
Circular SAR (CSAR) is a newly developed all-directional high resolution 3D imaging mode in recent years, to satisfy the demand of finer observation. The National Key Laboratory of Science and Technology on Microwave Imaging, Institute of Electronics, Chinese Academy of Sciences (MITL, IECAS), had the first test flight experiment in Aug. 2011 with a P-band full polarization SAR system, and successfully obtained the all-directional high resolution circular SAR image. The initial results show that CSAR technique has the encouraging potential capability in the fields of high precision mapping, disaster evaluation, resource management and the other related applications. This paper firstly makes a detailed discussion on the progress of circular SAR imaging technique, which emphases on the several airborne experiments performed these years to show CSARs attractive features, then studies and illustrates the key techniques, and finally discusses the development trends.
Circular SAR (CSAR) is a newly developed all-directional high resolution 3D imaging mode in recent years, to satisfy the demand of finer observation. The National Key Laboratory of Science and Technology on Microwave Imaging, Institute of Electronics, Chinese Academy of Sciences (MITL, IECAS), had the first test flight experiment in Aug. 2011 with a P-band full polarization SAR system, and successfully obtained the all-directional high resolution circular SAR image. The initial results show that CSAR technique has the encouraging potential capability in the fields of high precision mapping, disaster evaluation, resource management and the other related applications. This paper firstly makes a detailed discussion on the progress of circular SAR imaging technique, which emphases on the several airborne experiments performed these years to show CSARs attractive features, then studies and illustrates the key techniques, and finally discusses the development trends.
2012, 1(2): 136-142.
A High-speed digital sampling technology suitable for periodical impulse radar signal is proposed in this paper. One bit high-speed quantize is constructed by differential comparator in FPGA. Time-interleaved digital sampling and buffer encoding are used to one bit stream based on the internal multi-phase clock of FPGA, to achieve sampling rate higher than 1 GHz. High speed digital sampling is realized by the accumulation of one bit sampling data with different comparison levels. An 8 bit, 1.6 GHz ADC based on the proposed method is realized on XC2V3000 Xilinxs FPGA, which is successfully applied in GPR. The proposed method has the advantages of low cost and power consumption as compared with real sampling, and exhibits higher efficiency as compared with equivalent sampling.
A High-speed digital sampling technology suitable for periodical impulse radar signal is proposed in this paper. One bit high-speed quantize is constructed by differential comparator in FPGA. Time-interleaved digital sampling and buffer encoding are used to one bit stream based on the internal multi-phase clock of FPGA, to achieve sampling rate higher than 1 GHz. High speed digital sampling is realized by the accumulation of one bit sampling data with different comparison levels. An 8 bit, 1.6 GHz ADC based on the proposed method is realized on XC2V3000 Xilinxs FPGA, which is successfully applied in GPR. The proposed method has the advantages of low cost and power consumption as compared with real sampling, and exhibits higher efficiency as compared with equivalent sampling.
2012, 1(2): 143-148.
Distributed Compressed Sensing (DCS) extends compressive sampling from single signal to multi-signal ensembles. It also enables joint recovery that exploits both intra- and inter-signal correlation structures. Statistical MIMO radar systems that are made up of widely separated transmit/receive antennas form distributed detection systems for targets among transmitters, targets and receivers. In this paper, DCS is applied to statistical MIMO radars, and through the analysis of sparisty of the delays of target echo signals in the range space, the idea is proposed to construct target scene by joining all received signals. It also establishes the joint sparsity model of received signals, and gives joint reconstruction algorithms that can estimate target parameters. Simulation results show that, compared with the algorithm based on CS, the one based on DCS increases the parameter estimation accuracy while offering a reduction in the number of measurements. It is also validated that DCS -MIMO radars can effectively overcome target RCS fluctuations.
Distributed Compressed Sensing (DCS) extends compressive sampling from single signal to multi-signal ensembles. It also enables joint recovery that exploits both intra- and inter-signal correlation structures. Statistical MIMO radar systems that are made up of widely separated transmit/receive antennas form distributed detection systems for targets among transmitters, targets and receivers. In this paper, DCS is applied to statistical MIMO radars, and through the analysis of sparisty of the delays of target echo signals in the range space, the idea is proposed to construct target scene by joining all received signals. It also establishes the joint sparsity model of received signals, and gives joint reconstruction algorithms that can estimate target parameters. Simulation results show that, compared with the algorithm based on CS, the one based on DCS increases the parameter estimation accuracy while offering a reduction in the number of measurements. It is also validated that DCS -MIMO radars can effectively overcome target RCS fluctuations.
2012, 1(2): 149-156.
Because MUSIC (MUltiple SIgnal Classification) algorithm needs a large number of multiplications and trigonometric function evaluations, it is weak in the real time processing. This paper is aim at resolving above problem. Firstly, by analyzing the structural features of the uniform circular array and the uniform linear array, some properties of steering vector are extracted. Then, the properties of Hermite matrix are employed to decompose the complex multiplication, and then two real vectors are constructed to reduce the number of multiplications. Finally, with the properties of steering vector, a new algorithm based on look-up-table is proposed. The new algorithm neither has any trigonometric function evaluation, nor requires much memory space. The result of simulation experiments shows that the new algorithm raises the rate of MUSIC algorithm more than 50 times, while ensures the same estimated results. Therefore, the new algorithm has a wide application prospect.
Because MUSIC (MUltiple SIgnal Classification) algorithm needs a large number of multiplications and trigonometric function evaluations, it is weak in the real time processing. This paper is aim at resolving above problem. Firstly, by analyzing the structural features of the uniform circular array and the uniform linear array, some properties of steering vector are extracted. Then, the properties of Hermite matrix are employed to decompose the complex multiplication, and then two real vectors are constructed to reduce the number of multiplications. Finally, with the properties of steering vector, a new algorithm based on look-up-table is proposed. The new algorithm neither has any trigonometric function evaluation, nor requires much memory space. The result of simulation experiments shows that the new algorithm raises the rate of MUSIC algorithm more than 50 times, while ensures the same estimated results. Therefore, the new algorithm has a wide application prospect.
2012, 1(2): 157-162.
This paper performs aircraft attitude/heading estimation using an airborne dipole triad antenna. The signal model is given with the parameters such as the wave Direction Of Arrival (DOA) and state of polarization. The algorithms for estimating the source DOA and electric ellipse orientation angle are presented along with their statistical performance analysis. From these parameters, the aircraft gesture angles about pitching, yawing, and
rolling, which are needed by autopilot, are produced. Simulation results validate the proposed algorithms efficacy.
This paper performs aircraft attitude/heading estimation using an airborne dipole triad antenna. The signal model is given with the parameters such as the wave Direction Of Arrival (DOA) and state of polarization. The algorithms for estimating the source DOA and electric ellipse orientation angle are presented along with their statistical performance analysis. From these parameters, the aircraft gesture angles about pitching, yawing, and
rolling, which are needed by autopilot, are produced. Simulation results validate the proposed algorithms efficacy.
2012, 1(2): 163-170.
How to obtain high-resolution images of ship targets is an active research area in radar field due to the complexity of the ship motion. At the same time, multi-platform based surveillance and combat mode is gaining more and more interests in recent years. Based on the above situation, in this paper, a multistatic Inverse Synthetic Aperture Radar (ISAR) ship imaging method is presented, the method is capable of increasing the integration time for stationary imaging by deploying the multiple platforms with appropriate altitudes and aspect angles and coherently integrating the echoes received by each platform. Combined with the optimal imaging time selection scheme, this method can obtain side-view or top-view ship images with higher-resolution as compared to the monostatic radar. Simulations are performed to verify the effectiveness of our multistatic ISAR ship imaging method.
How to obtain high-resolution images of ship targets is an active research area in radar field due to the complexity of the ship motion. At the same time, multi-platform based surveillance and combat mode is gaining more and more interests in recent years. Based on the above situation, in this paper, a multistatic Inverse Synthetic Aperture Radar (ISAR) ship imaging method is presented, the method is capable of increasing the integration time for stationary imaging by deploying the multiple platforms with appropriate altitudes and aspect angles and coherently integrating the echoes received by each platform. Combined with the optimal imaging time selection scheme, this method can obtain side-view or top-view ship images with higher-resolution as compared to the monostatic radar. Simulations are performed to verify the effectiveness of our multistatic ISAR ship imaging method.
2012, 1(2): 171-181.
Based on the ratio distance pixel-relativity and thresholding pixel-similarity, a modified non-local filter is proposed for SAR image despeckling in this paper. Firstly, the ratio distance pixel-relativity is obtained by transforming the joint probability density function of two pixels. Then, a table of pixel-similarity threshold, as a function of the SAR image look number and neighboring reflectivity ratio, is trained according to the minimum error probability. Finally, the pixel-similarity threshold is applied to select similar pixels from the searching window for the real reflectivity estimation. The proposed approach was verified by synthetic and real SAR images, and was compared with the PPB and LHRS-PRM filters. The visual quality and the quantification comparison show that the proposed approach is excellent not only in the reconstruction of the uniform area, the character of edges, texture, and details, but also with the lower computation complexity.
Based on the ratio distance pixel-relativity and thresholding pixel-similarity, a modified non-local filter is proposed for SAR image despeckling in this paper. Firstly, the ratio distance pixel-relativity is obtained by transforming the joint probability density function of two pixels. Then, a table of pixel-similarity threshold, as a function of the SAR image look number and neighboring reflectivity ratio, is trained according to the minimum error probability. Finally, the pixel-similarity threshold is applied to select similar pixels from the searching window for the real reflectivity estimation. The proposed approach was verified by synthetic and real SAR images, and was compared with the PPB and LHRS-PRM filters. The visual quality and the quantification comparison show that the proposed approach is excellent not only in the reconstruction of the uniform area, the character of edges, texture, and details, but also with the lower computation complexity.
2012, 1(2): 182-189.
Focusing on the change detection with multitemporal Synthetic Aperture Radar (SAR) images, this paper presents a new approach based on the comparison of the density of the projections produced by Radon transform. The projections include the structure information, which helps when the local statistical distribution does not change. Edgeworth approach is used to fit the statistical distribution model of the projections. Jeffrey divergence is proposed as a measurement of the difference between two densities for that it is numerically stable and robust with respect to noise. This approach is demonstrated feasible according to the processing test using real satellite SAR images.
Focusing on the change detection with multitemporal Synthetic Aperture Radar (SAR) images, this paper presents a new approach based on the comparison of the density of the projections produced by Radon transform. The projections include the structure information, which helps when the local statistical distribution does not change. Edgeworth approach is used to fit the statistical distribution model of the projections. Jeffrey divergence is proposed as a measurement of the difference between two densities for that it is numerically stable and robust with respect to noise. This approach is demonstrated feasible according to the processing test using real satellite SAR images.
In this paper, a new approach for the understanding of the SAR image of the cylinder oil tank is presented. In the approach, the Physical Optics (PO) and the theory of Incremental Length Diffraction Coefficients (ILDC) are employed to set up the scattering model of the oil tank according to the circle edges and cylinder geometry futures, and the position of the main scattering centers are deduced. The SAR image of the tank is simulated through the scattering model and the imaging model based on Mapping andProjection Algorithm (MPA). The real SAR data and the simulation test the validity of the approach. Furthermore, the scattering centers are detected with 45 groups of the measured data. According the scattering model and the imaging model in the approach proposed, the main scattering characteristics of the cylindrical oil tank are interpreted and summarized. It is hoped that the work in this paper could provide some useful guidelines for the identification of the oil tank in the SAR images.
In this paper, a new approach for the understanding of the SAR image of the cylinder oil tank is presented. In the approach, the Physical Optics (PO) and the theory of Incremental Length Diffraction Coefficients (ILDC) are employed to set up the scattering model of the oil tank according to the circle edges and cylinder geometry futures, and the position of the main scattering centers are deduced. The SAR image of the tank is simulated through the scattering model and the imaging model based on Mapping andProjection Algorithm (MPA). The real SAR data and the simulation test the validity of the approach. Furthermore, the scattering centers are detected with 45 groups of the measured data. According the scattering model and the imaging model in the approach proposed, the main scattering characteristics of the cylindrical oil tank are interpreted and summarized. It is hoped that the work in this paper could provide some useful guidelines for the identification of the oil tank in the SAR images.
2012, 1(2): 196-202.
Phase unwrapping is a key issue in InSAR research. As a critical step of InSAR processing, it affects the
accuracy of interferometry measurement directly. The efficiency of the traditional quality-guided phase unwrapping method is low due to a great deal of sorting, espceically for large interferogram. This paper proposes a highly efficient quality-guided phase unwrapping method based on heap sort in order to solve the problem. First, the quality map is caculated according to the interferometric complex data or interferogram. Next, with the max-heap acting as the data structure of sorting, its property is maintained while deleting root node and inserting new node, and thus the sorting of quality map is accomplished and the phase can be unwrapped from high quality areas to low quality areas. The improved algorithm reduces the computational complexity greatly compared with traditional methods, which is significant in large area mapping of InSAR. At the end of the paper, the simulated and experimental results show the accuracy and the efficiency of the algorithm.
Phase unwrapping is a key issue in InSAR research. As a critical step of InSAR processing, it affects the
accuracy of interferometry measurement directly. The efficiency of the traditional quality-guided phase unwrapping method is low due to a great deal of sorting, espceically for large interferogram. This paper proposes a highly efficient quality-guided phase unwrapping method based on heap sort in order to solve the problem. First, the quality map is caculated according to the interferometric complex data or interferogram. Next, with the max-heap acting as the data structure of sorting, its property is maintained while deleting root node and inserting new node, and thus the sorting of quality map is accomplished and the phase can be unwrapped from high quality areas to low quality areas. The improved algorithm reduces the computational complexity greatly compared with traditional methods, which is significant in large area mapping of InSAR. At the end of the paper, the simulated and experimental results show the accuracy and the efficiency of the algorithm.
2012, 1(2): 203-208.
Finite element modeling and structural dynamic characteristics of antenna pedestal in airborne SAR were studied in this paper. The Finite element model of antenna pedestal in airborne SAR was set up on the basis of structural dynamic theory, then, the key technologies of dynamic simulation were pointed out, and the modal analysis and transient analysis were carried out. Simulation results show that the dynamic characteristics of antenna pedestal in airborne SAR can meet the requirements of servo bandwidth and structural strength. The fast finite element modeling and simulation method proposed in this paper are of great significance to the weight reducing design of antenna pedestal in airborne SAR.
Finite element modeling and structural dynamic characteristics of antenna pedestal in airborne SAR were studied in this paper. The Finite element model of antenna pedestal in airborne SAR was set up on the basis of structural dynamic theory, then, the key technologies of dynamic simulation were pointed out, and the modal analysis and transient analysis were carried out. Simulation results show that the dynamic characteristics of antenna pedestal in airborne SAR can meet the requirements of servo bandwidth and structural strength. The fast finite element modeling and simulation method proposed in this paper are of great significance to the weight reducing design of antenna pedestal in airborne SAR.
2012, 1(2): 209-216.
A concept of a bi-static geosynchronous synthetic aperture system, which is formed by reusing backscattered signals of Compass Navigation Satellite System (CNSS), is proposed. The geometric relations of a geostationary satellite of CNSS, located on a geosynchronous satellite receiver, which is illuminated by the backscattered energy of a satellite of CNSS, and a ground station is built up, and following the relations as well as principle of synthetic aperture radar, we expatiate the feasibility of the system by considering parameters such as imaging resolution, ratio of signal to noise and link budget, etc.. Besides, the potential remote sensing applications for measurement of terrain humidity, characteristics of space-time dynamics of changing of terrain surface and atmospheric characteristic, etc..
A concept of a bi-static geosynchronous synthetic aperture system, which is formed by reusing backscattered signals of Compass Navigation Satellite System (CNSS), is proposed. The geometric relations of a geostationary satellite of CNSS, located on a geosynchronous satellite receiver, which is illuminated by the backscattered energy of a satellite of CNSS, and a ground station is built up, and following the relations as well as principle of synthetic aperture radar, we expatiate the feasibility of the system by considering parameters such as imaging resolution, ratio of signal to noise and link budget, etc.. Besides, the potential remote sensing applications for measurement of terrain humidity, characteristics of space-time dynamics of changing of terrain surface and atmospheric characteristic, etc..
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