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Editor Work2014 Vol. 3, No. 2
Previous Issue
2014, 3(2): 119-128.
Abstract
1870KB
Based on ElectroMagnetic (EM) theory and the monopulse radar angle measurement principle, the formulae of angular glint for complex target are proposed and generally applied to tackling practical problems. The inherent relations among the three representations of radar angular glint, i.e. the phase-front distortion concept, the energy-flow tilt concept, and the monopulse radar angular noise concept, are clearly demonstrated. The two existing concepts of angular glint are also revised. Thus, a firm theoretical foundation for understanding, modeling, simulating and suppressing the angular glint from complex radar targets is established.
Based on ElectroMagnetic (EM) theory and the monopulse radar angle measurement principle, the formulae of angular glint for complex target are proposed and generally applied to tackling practical problems. The inherent relations among the three representations of radar angular glint, i.e. the phase-front distortion concept, the energy-flow tilt concept, and the monopulse radar angular noise concept, are clearly demonstrated. The two existing concepts of angular glint are also revised. Thus, a firm theoretical foundation for understanding, modeling, simulating and suppressing the angular glint from complex radar targets is established.
2014, 3(2): 129-141.
For the high-speed, high-maneuverability and stealthy target detection via modern radar in complicated electromagnetic environment, a novel radar signal processing approach called Space-Time-Frequency Focus-Before-Detection (STF-FBD) via multi-dimensional coherent integration is proposed. Based on space-timefrequency signal modeling for modern radar systems, the proposed method can effectively suppress the strong interference, such as clutter and active jamming, and overcome the problems of scaled effect of high-speed targets, aperture fill time, sparse frequency sub-band synthesis, across range units, across Doppler units and across beam units. The proposed methods improves radar signal processing performance on the steps like energy integration, target detection, parameter estimation, maneuver tracking, feature extraction and target recognition. It also outperforms the existing Track-Before-Detection (TBD) methods and establish a unified STF-FBD and STF-FBD-TBD radar signal processing frame work. The proposed method is suitable for high-speed, high-maneuverability and stealthy target, as well as for conventional targets. It is applicable for new-generation modern radar, as well as for conventional radars, and may find application to different field.
For the high-speed, high-maneuverability and stealthy target detection via modern radar in complicated electromagnetic environment, a novel radar signal processing approach called Space-Time-Frequency Focus-Before-Detection (STF-FBD) via multi-dimensional coherent integration is proposed. Based on space-timefrequency signal modeling for modern radar systems, the proposed method can effectively suppress the strong interference, such as clutter and active jamming, and overcome the problems of scaled effect of high-speed targets, aperture fill time, sparse frequency sub-band synthesis, across range units, across Doppler units and across beam units. The proposed methods improves radar signal processing performance on the steps like energy integration, target detection, parameter estimation, maneuver tracking, feature extraction and target recognition. It also outperforms the existing Track-Before-Detection (TBD) methods and establish a unified STF-FBD and STF-FBD-TBD radar signal processing frame work. The proposed method is suitable for high-speed, high-maneuverability and stealthy target, as well as for conventional targets. It is applicable for new-generation modern radar, as well as for conventional radars, and may find application to different field.
2014, 3(2): 142-149.
A frequency-domain method is proposed for wideband radar echo simulation of high-speed moving targets. Based on the physical process of electromagnetic waves observing a moving target, a frequency-domain echo model of wideband radar is constructed, and the block diagram of the radar echo simulation in frequency-domain is presented. Then, the impacts of radial velocity and slant range on the matching filtering of LFM radar are analyzed, and some quantitative conclusions on the shift and expansion of the radar profiles are obtained. Simulation results illustrate the correctness and efficiency of the proposed method.
A frequency-domain method is proposed for wideband radar echo simulation of high-speed moving targets. Based on the physical process of electromagnetic waves observing a moving target, a frequency-domain echo model of wideband radar is constructed, and the block diagram of the radar echo simulation in frequency-domain is presented. Then, the impacts of radial velocity and slant range on the matching filtering of LFM radar are analyzed, and some quantitative conclusions on the shift and expansion of the radar profiles are obtained. Simulation results illustrate the correctness and efficiency of the proposed method.
2014, 3(2): 150-157.
To simulate dynamic Radar Cross Section (RCS) of missile target group, an efficient RCS prediction approach is proposed based on the high-frequency asymptotic theory. The minimal energy trajectory and coordinate transformation is used to get trajectories of the missile, decoys and roll booster, and establish the dynamic scene for the separate procedure of the target group, and the dynamic RCS including specular reflection, edge diffraction and multi-reflection from the target group are obtained by Physical Optics (PO), Equivalent Edge Currents (EEC) and Shooting-and-Bouncing Ray (SBR) methods. Compared with the dynamic RCS result with the common interpolation method, the proposed method is consistent with the common method when the targets in the scene are far away from each other and each target is not sheltered by others in the incident direction. When the target group is densely distributed and the shelter effect can not be neglected, the interpolation method is extremely difficult to realize, whereas the proposed method is successful.
To simulate dynamic Radar Cross Section (RCS) of missile target group, an efficient RCS prediction approach is proposed based on the high-frequency asymptotic theory. The minimal energy trajectory and coordinate transformation is used to get trajectories of the missile, decoys and roll booster, and establish the dynamic scene for the separate procedure of the target group, and the dynamic RCS including specular reflection, edge diffraction and multi-reflection from the target group are obtained by Physical Optics (PO), Equivalent Edge Currents (EEC) and Shooting-and-Bouncing Ray (SBR) methods. Compared with the dynamic RCS result with the common interpolation method, the proposed method is consistent with the common method when the targets in the scene are far away from each other and each target is not sheltered by others in the incident direction. When the target group is densely distributed and the shelter effect can not be neglected, the interpolation method is extremely difficult to realize, whereas the proposed method is successful.
2014, 3(2): 158-165.
To suppress airwave interference, a time-domain coded electromagnetic exploration method is proposed with Pseudo-Random Binary Sequences (PRBS) code as the source signal. Based on the PRBS code and receiving voltages, which are recorded simultaneously, the impulse response of the earth can be obtained by the time-domain deconvolution signal recovery method, and the target information is effectively contained in the impulse response. The selection methods of clock frequency and code length were analyzed and field experiments were carried out, which demonstrated that the signal quality of the EM data could be improved by decreasing the clock frequency, or increasing the code length. The proposed method could greatly suppress the airwave interference and effectively identify underground anomalies.
To suppress airwave interference, a time-domain coded electromagnetic exploration method is proposed with Pseudo-Random Binary Sequences (PRBS) code as the source signal. Based on the PRBS code and receiving voltages, which are recorded simultaneously, the impulse response of the earth can be obtained by the time-domain deconvolution signal recovery method, and the target information is effectively contained in the impulse response. The selection methods of clock frequency and code length were analyzed and field experiments were carried out, which demonstrated that the signal quality of the EM data could be improved by decreasing the clock frequency, or increasing the code length. The proposed method could greatly suppress the airwave interference and effectively identify underground anomalies.
2014, 3(2): 166-175.
Interferometry filtering is one of the key steps in obtain high-precision Digital Elevation Model (DEM) and Digital Orthophoto Map (DOM). In the case of low-correlation or complicated topography, traditional phase filtering methods fail in balancing noise elimination and phase preservation, which leads to inaccurate interferometric phase. This paper proposed an adaptive iterated nonlocal interferometry filtering method to deal with the problem. Based on the thought of nonlocal filtering, the proposed method filters the image with utilization of the image redundancy information. The smoothing parameter of the method is adaptive to the interferometry, and automatic iteration, in which the window size is adjusted, is applied to improve the filtering precision. Validity of the proposed method is verified by simulated and real data. Comparison with existed methods is given at the same time.
Interferometry filtering is one of the key steps in obtain high-precision Digital Elevation Model (DEM) and Digital Orthophoto Map (DOM). In the case of low-correlation or complicated topography, traditional phase filtering methods fail in balancing noise elimination and phase preservation, which leads to inaccurate interferometric phase. This paper proposed an adaptive iterated nonlocal interferometry filtering method to deal with the problem. Based on the thought of nonlocal filtering, the proposed method filters the image with utilization of the image redundancy information. The smoothing parameter of the method is adaptive to the interferometry, and automatic iteration, in which the window size is adjusted, is applied to improve the filtering precision. Validity of the proposed method is verified by simulated and real data. Comparison with existed methods is given at the same time.
2014, 3(2): 176-182.
The Back Projection (BP) algorithm is a very important time-domain methodology for Synthetic Aperture Radar (SAR) imaging. However, conventional autofocus techniques are based on frequency-domain imaging algorithms, and can not be directly applied to BP imagery for error phase estimation. In this paper, an autofocus algorithm for BP imagery is proposed. The algorithm takes image sharpness as an objective function, and employs the coordinate descent optimization scheme to obtain the optimum phase-corrected variables by iterations. In the implementation, with a Legendre approximation of the objective function, the optimal phase estimation can be found analytically for each parameter within an iteration, avoiding computationally expensive line-search procedures. The experimental results with both simulated and measured data confirm the accuracy and effectiveness of the proposed algorithm.
The Back Projection (BP) algorithm is a very important time-domain methodology for Synthetic Aperture Radar (SAR) imaging. However, conventional autofocus techniques are based on frequency-domain imaging algorithms, and can not be directly applied to BP imagery for error phase estimation. In this paper, an autofocus algorithm for BP imagery is proposed. The algorithm takes image sharpness as an objective function, and employs the coordinate descent optimization scheme to obtain the optimum phase-corrected variables by iterations. In the implementation, with a Legendre approximation of the objective function, the optimal phase estimation can be found analytically for each parameter within an iteration, avoiding computationally expensive line-search procedures. The experimental results with both simulated and measured data confirm the accuracy and effectiveness of the proposed algorithm.
2014, 3(2): 183-191.
The airborne interferometric SAR platform suffers from instability factors, such as air turbulence and mechanical vibrations during flight. Such factors cause the oscillation of the flexible baseline, which leads to significant degradation of the performance of the interferometric SAR system. This study is concerned with the baseline oscillation. First, the error of the slant range model under baseline oscillation conditions is formulated. Then, the SAR complex image signal and dual-channel correlation coefficient are modeled based on the first-order, second-order, and generic slant range error. Subsequently, the impact of the baseline oscillation on the imaging and interferometric performance of the SAR system is analyzed. Finally, simulations of the echo data are used to validate the theoretical analysis of the baseline oscillation in the airborne interferometric SAR.
The airborne interferometric SAR platform suffers from instability factors, such as air turbulence and mechanical vibrations during flight. Such factors cause the oscillation of the flexible baseline, which leads to significant degradation of the performance of the interferometric SAR system. This study is concerned with the baseline oscillation. First, the error of the slant range model under baseline oscillation conditions is formulated. Then, the SAR complex image signal and dual-channel correlation coefficient are modeled based on the first-order, second-order, and generic slant range error. Subsequently, the impact of the baseline oscillation on the imaging and interferometric performance of the SAR system is analyzed. Finally, simulations of the echo data are used to validate the theoretical analysis of the baseline oscillation in the airborne interferometric SAR.
2014, 3(2): 192-200.
Bistatic Synthetic Aperture Radar (BiSAR) in one-stationary mode has many advantages over the traditional monostatic SAR. Its echo, however, shows serious space variance in both range and azimuth directions due to its complex imaging geometry, making it hard to be processed by the frequency methods used in the monostatic SAR. To solve that problem, a method based on blocks and interpolation has been proposed by Wang Yu et al.. With this method, points can be well focused except for those located on the edge of each block. In this paper, a modified method is put forward, which adopts new block-dividing strategy and new mapping relationship in the interpolation. With the proposed method, points on the edge can also be well focused, making the quality of the final image greatly improved.
Bistatic Synthetic Aperture Radar (BiSAR) in one-stationary mode has many advantages over the traditional monostatic SAR. Its echo, however, shows serious space variance in both range and azimuth directions due to its complex imaging geometry, making it hard to be processed by the frequency methods used in the monostatic SAR. To solve that problem, a method based on blocks and interpolation has been proposed by Wang Yu et al.. With this method, points can be well focused except for those located on the edge of each block. In this paper, a modified method is put forward, which adopts new block-dividing strategy and new mapping relationship in the interpolation. With the proposed method, points on the edge can also be well focused, making the quality of the final image greatly improved.
2014, 3(2): 201-207.
Compared with Space-Time Adaptive Processing (STAP), Space-Time Adaptive Detection (STAD) employs the data in the cell under test and those in the training to form reasonable detection statistics and consequently decides whether the target exists or not. The STAD has concise processing procedure and flexible design. Furthermore, the detection statistics usually possess the Constant False Alarm Rate (CFAR) property, and hence it needs no additional CFAR processing. More importantly, the STAD usually exhibits improved detection performance than that of the conventional processing, which first suppresses the clutter then adopts other detection strategy. In this paper, we first summarize the key strongpoint of the STAD, then make a classification for the STAD, and finally give some future research tracks.
Compared with Space-Time Adaptive Processing (STAP), Space-Time Adaptive Detection (STAD) employs the data in the cell under test and those in the training to form reasonable detection statistics and consequently decides whether the target exists or not. The STAD has concise processing procedure and flexible design. Furthermore, the detection statistics usually possess the Constant False Alarm Rate (CFAR) property, and hence it needs no additional CFAR processing. More importantly, the STAD usually exhibits improved detection performance than that of the conventional processing, which first suppresses the clutter then adopts other detection strategy. In this paper, we first summarize the key strongpoint of the STAD, then make a classification for the STAD, and finally give some future research tracks.
2014, 3(2): 208-216.
The transmit angle of bistatic radars can be obtained by introducing Multiple-Input Multiple-Output (MIMO) radar techniques. The Three-Dimensional (3D) clutter spectra, that is, the transmit angle, receive angle, and Doppler frequency, are introduced using the additional angle information to Space-Time Adaptive Processing (STAP). This study reviews the researches on bistatic MIMO-STAP. 3D space-time adaptive processing methods for airborne bistatic side-looking MIMO radars, such as 3D-LCMV, 3D-ACR, 3D-JDL, and 3D projection-based reduced dimensional STAP methods, are discussed. Simulation results show that the proposed methods can improve the small-sample support performance of range-dependent clutter suppression in bistatic side-looking MIMO radar. Finally, the results are summarized and the prospects of bistatic MIMO-STAP are discussed.
The transmit angle of bistatic radars can be obtained by introducing Multiple-Input Multiple-Output (MIMO) radar techniques. The Three-Dimensional (3D) clutter spectra, that is, the transmit angle, receive angle, and Doppler frequency, are introduced using the additional angle information to Space-Time Adaptive Processing (STAP). This study reviews the researches on bistatic MIMO-STAP. 3D space-time adaptive processing methods for airborne bistatic side-looking MIMO radars, such as 3D-LCMV, 3D-ACR, 3D-JDL, and 3D projection-based reduced dimensional STAP methods, are discussed. Simulation results show that the proposed methods can improve the small-sample support performance of range-dependent clutter suppression in bistatic side-looking MIMO radar. Finally, the results are summarized and the prospects of bistatic MIMO-STAP are discussed.
2014, 3(2): 217-228.
This paper gives a brief review on the Sparse-Recovery (SR)-based Space-Time Adaptive Processing (STAP) technique. First, the motivation for introducing sparse recovery into STAP is presented. Next, the potential advantages and mathematical explanation of the sparse-recovery-based STAP are discussed. A major part of this paper presents the state-of-art research results in spatio-temporal spectrum-sparsity-based STAP, including the basic frame, off-grid problem, multiple measurement vector problem, and direct domain problem. The sparse-recovery-based STAP on conformal array problem is also introduced. Finally, a summary of sparse-recovery-based STAP is provided, and the problems that need to be solved and some potential research areas are discussed.
This paper gives a brief review on the Sparse-Recovery (SR)-based Space-Time Adaptive Processing (STAP) technique. First, the motivation for introducing sparse recovery into STAP is presented. Next, the potential advantages and mathematical explanation of the sparse-recovery-based STAP are discussed. A major part of this paper presents the state-of-art research results in spatio-temporal spectrum-sparsity-based STAP, including the basic frame, off-grid problem, multiple measurement vector problem, and direct domain problem. The sparse-recovery-based STAP on conformal array problem is also introduced. Finally, a summary of sparse-recovery-based STAP is provided, and the problems that need to be solved and some potential research areas are discussed.
2014, 3(2): 229-234.
Sparse recovery Space-Time Adaptive Processing (STAP) methods for obtaining the clutter spectrum require few training samples and can effectively suppress clutter in nonhomogeneous clutter environments. However, presently available sparse recovery STAP methods only use single training samples to recover the clutter spectrum, neglecting information from multiple samples. Moreover, the recovery performance of the abovementioned methods is sensitive to noise. In this study, a subspace-based jointly sparse recovery method is proposed. The information from multiple training samples is fully used and robust clutter suppression performance in noisy environments is achieved. Simulation results show the effectiveness of the proposed method.
Sparse recovery Space-Time Adaptive Processing (STAP) methods for obtaining the clutter spectrum require few training samples and can effectively suppress clutter in nonhomogeneous clutter environments. However, presently available sparse recovery STAP methods only use single training samples to recover the clutter spectrum, neglecting information from multiple samples. Moreover, the recovery performance of the abovementioned methods is sensitive to noise. In this study, a subspace-based jointly sparse recovery method is proposed. The information from multiple training samples is fully used and robust clutter suppression performance in noisy environments is achieved. Simulation results show the effectiveness of the proposed method.
An Efficient STAP Algorithm for Nonsidelooking Airborne Radar Based on Mainlobe Clutter Compensation
2014, 3(2): 235-240.
An efficient STAP algorithm for NonSideLooking (NSL) airborne radar is presented. The algorithm can mitigate the range dependence of clutter by mainlobe clutter compensation. To reduce the computational complexity, the Doppler frequency of the mainlobe clutter is firstly estimated via FFT in the time domain, and then the spatial frequency is accurately obtained by sparse reconstruction corresponding to the output of the mainlobe clutter Doppler cell. Therefore, based on the estimated location of the mainlobe clutter, the clutter corresponding to different range cells can be adaptively compensated, which results in improved clutter suppression performance of the following 3DT processing. As shown in the simulation, the Improvement Factor (IF) of 3DT is increased about 18 dB in the domain of mainlobe, which can greatly improve the detection of slowmoving targets. In addition, the proposed scheme can be applied to real-time processing owing to its small computational load.
An efficient STAP algorithm for NonSideLooking (NSL) airborne radar is presented. The algorithm can mitigate the range dependence of clutter by mainlobe clutter compensation. To reduce the computational complexity, the Doppler frequency of the mainlobe clutter is firstly estimated via FFT in the time domain, and then the spatial frequency is accurately obtained by sparse reconstruction corresponding to the output of the mainlobe clutter Doppler cell. Therefore, based on the estimated location of the mainlobe clutter, the clutter corresponding to different range cells can be adaptively compensated, which results in improved clutter suppression performance of the following 3DT processing. As shown in the simulation, the Improvement Factor (IF) of 3DT is increased about 18 dB in the domain of mainlobe, which can greatly improve the detection of slowmoving targets. In addition, the proposed scheme can be applied to real-time processing owing to its small computational load.
2014, 3(2): 241-248.
The Displaced Phase Center Antenna (DPCA) technology, a particular form of Space Time Adaptive Processing (STAP), has been widely used in Synthetic Aperture Radar Ground Moving Target Indication (SAR-GMTI). The GMTI performance depends on the capability of clutter rejection but the traditional DPCA technology operated in the complex image domain does not have the appropriate clutter rejection capability for urban areas with strong scattering stationary objects. Hence, interferometry phase is used to weight the DPCA magnitude nonlinearly, and a weighted DPCA clutter rejection approach is proposed, which reduces the interference from residual phase difference. The experimental results suggest that the new approach can improve the clutter rejection compared with the conventional DPCA.
The Displaced Phase Center Antenna (DPCA) technology, a particular form of Space Time Adaptive Processing (STAP), has been widely used in Synthetic Aperture Radar Ground Moving Target Indication (SAR-GMTI). The GMTI performance depends on the capability of clutter rejection but the traditional DPCA technology operated in the complex image domain does not have the appropriate clutter rejection capability for urban areas with strong scattering stationary objects. Hence, interferometry phase is used to weight the DPCA magnitude nonlinearly, and a weighted DPCA clutter rejection approach is proposed, which reduces the interference from residual phase difference. The experimental results suggest that the new approach can improve the clutter rejection compared with the conventional DPCA.
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