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Editor Work2017 Vol. 6, No. 4
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2017, 6(4): 325-331.
Abstract
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Due to the effect of range-Doppler coupling between the time delay and shifted frequency of an LFM waveform, LFM radar is particularly susceptible to shift frequency jamming. A new deceptive jamming method, the Preceded Frequency-shift False Target (PFFT), has a similar signature to real radar targets, which indicates that conventional ECCM, such as leading-edge tracking, could be invalid when countering it. In this paper, the basic principle of PFFT is introduced and its signatures analyzed. Then, a new method for discrimination between a preceded false target generated by Digital Radio Frequency Memory (DRFM) and a radar target is proposed. By comparing the echo arrival time at the radar receiver front end with that estimated after a matched filter, the new method can extract the frequency modulation jamming signature and make a correct judgment. Simulation results are presented to verify the validity of the proposed method.
Due to the effect of range-Doppler coupling between the time delay and shifted frequency of an LFM waveform, LFM radar is particularly susceptible to shift frequency jamming. A new deceptive jamming method, the Preceded Frequency-shift False Target (PFFT), has a similar signature to real radar targets, which indicates that conventional ECCM, such as leading-edge tracking, could be invalid when countering it. In this paper, the basic principle of PFFT is introduced and its signatures analyzed. Then, a new method for discrimination between a preceded false target generated by Digital Radio Frequency Memory (DRFM) and a radar target is proposed. By comparing the echo arrival time at the radar receiver front end with that estimated after a matched filter, the new method can extract the frequency modulation jamming signature and make a correct judgment. Simulation results are presented to verify the validity of the proposed method.
2017, 6(4): 332-339.
By the synthesis of multi-radar electromagnetic wave space energy, Distributed Aperture Coherence-synthetic Radar (DACR) achieves long-range power detection via multi-radar airspace expansion to realize high-precision target angle measurement. DACR has the advantages of strong survival ability, a high cost-effectiveness ratio, high angular accuracy, strong expandability, and easy realization. In this article, we analyze the joint antenna gain of a non-directional multi-point source and, given the theoretical derivation and simulation analysis, we establish a distributed-array-antenna geometric model, analyze the joint antenna pattern and gain, respectively, and determine that the joint antenna gain is approximately equal to the unit radar number and the unit radar gain product. Lastly, we perform a joint antenna gain simulation using HFSS software to further verify the joint antenna gain results.
By the synthesis of multi-radar electromagnetic wave space energy, Distributed Aperture Coherence-synthetic Radar (DACR) achieves long-range power detection via multi-radar airspace expansion to realize high-precision target angle measurement. DACR has the advantages of strong survival ability, a high cost-effectiveness ratio, high angular accuracy, strong expandability, and easy realization. In this article, we analyze the joint antenna gain of a non-directional multi-point source and, given the theoretical derivation and simulation analysis, we establish a distributed-array-antenna geometric model, analyze the joint antenna pattern and gain, respectively, and determine that the joint antenna gain is approximately equal to the unit radar number and the unit radar gain product. Lastly, we perform a joint antenna gain simulation using HFSS software to further verify the joint antenna gain results.
2017, 6(4): 340-348.
To obtain an accurate polarization scattering matrix, simultaneous full polarization radar systems must transmit two signals. The performance of orthogonal polyphase codes designed by the traditional method is limited by the code length and is sensitive to Doppler frequency. In this paper, we propose a design method for orthogonal polyphase codes that have good Doppler tolerance. We consider the peak sidelobe level and isolation and transform the signal design problem into a nonlinear optimization problem, which we solve using a genetic algorithm. Our simulation results show that our proposed orthogonal polyphase codes have better Doppler tolerance and their peak sidelobe levels and orthogonal performances are 1.5～2 dB better than the codes designed by Deng or Khan. As such, the new design can improve the measurement accuracy of simultaneous full polarization radar systems.
To obtain an accurate polarization scattering matrix, simultaneous full polarization radar systems must transmit two signals. The performance of orthogonal polyphase codes designed by the traditional method is limited by the code length and is sensitive to Doppler frequency. In this paper, we propose a design method for orthogonal polyphase codes that have good Doppler tolerance. We consider the peak sidelobe level and isolation and transform the signal design problem into a nonlinear optimization problem, which we solve using a genetic algorithm. Our simulation results show that our proposed orthogonal polyphase codes have better Doppler tolerance and their peak sidelobe levels and orthogonal performances are 1.5～2 dB better than the codes designed by Deng or Khan. As such, the new design can improve the measurement accuracy of simultaneous full polarization radar systems.
2017, 6(4): 349-358.
To investigate the problems of the large grayscale difference between infrared and Synthetic Aperture Radar (SAR) images and their fusion image not being fit for human visual perception, we propose a fusion method for SAR and infrared images in the complex contourlet domain based on joint sparse representation. First, we perform complex contourlet decomposition of the infrared and SAR images. Then, we employ the K-Singular Value Decomposition (K-SVD) method to obtain an over-complete dictionary of the low-frequency components of the two source images. Using a joint sparse representation model, we then generate a joint dictionary. We obtain the sparse representation coefficients of the low-frequency components of the source images in the joint dictionary by the Orthogonal Matching Pursuit (OMP) method and select them using the selection maximization strategy. We then reconstruct these components to obtain the fused low-frequency components and fuse the high-frequency components using two criteria——the coefficient of visual sensitivity and the degree of energy matching. Finally, we obtain the fusion image by the inverse complex contourlet transform. Compared with the three classical fusion methods and recently presented fusion methods, e.g., that based on the Non-Subsampled Contourlet Transform (NSCT) and another based on sparse representation, the method we propose in this paper can effectively highlight the salient features of the two source images and inherit their information to the greatest extent.
To investigate the problems of the large grayscale difference between infrared and Synthetic Aperture Radar (SAR) images and their fusion image not being fit for human visual perception, we propose a fusion method for SAR and infrared images in the complex contourlet domain based on joint sparse representation. First, we perform complex contourlet decomposition of the infrared and SAR images. Then, we employ the K-Singular Value Decomposition (K-SVD) method to obtain an over-complete dictionary of the low-frequency components of the two source images. Using a joint sparse representation model, we then generate a joint dictionary. We obtain the sparse representation coefficients of the low-frequency components of the source images in the joint dictionary by the Orthogonal Matching Pursuit (OMP) method and select them using the selection maximization strategy. We then reconstruct these components to obtain the fused low-frequency components and fuse the high-frequency components using two criteria——the coefficient of visual sensitivity and the degree of energy matching. Finally, we obtain the fusion image by the inverse complex contourlet transform. Compared with the three classical fusion methods and recently presented fusion methods, e.g., that based on the Non-Subsampled Contourlet Transform (NSCT) and another based on sparse representation, the method we propose in this paper can effectively highlight the salient features of the two source images and inherit their information to the greatest extent.
2017, 6(4): 359-367.
In this paper, we present a shading jamming method for the Synthetic Aperture Radar and Ground Moving Target Indicator (SAR-GMTI). This method begins with intermittently sampling intercepted SAR signals, performing motion modulation, and then transmitting them. The motion modulation of SAR signals can produce a motion modulation effect and intermittent sampling repeater jamming can produce multi-fronted and lagged false targets along a range. Their combination provides a jamming effect of smart shading areas, which can’t be cancelled after multi-channel cancelling. The uniqueness of this jamming method is that the energy only appears on the moving target to be covered, so less jamming energy is needed. We analyzed the proposed jamming principle against GMTI using the tri-channel interference cancelling technique. Our simulation results verify our analyses and confirm its jamming effectiveness for SAR-GMTI.
In this paper, we present a shading jamming method for the Synthetic Aperture Radar and Ground Moving Target Indicator (SAR-GMTI). This method begins with intermittently sampling intercepted SAR signals, performing motion modulation, and then transmitting them. The motion modulation of SAR signals can produce a motion modulation effect and intermittent sampling repeater jamming can produce multi-fronted and lagged false targets along a range. Their combination provides a jamming effect of smart shading areas, which can’t be cancelled after multi-channel cancelling. The uniqueness of this jamming method is that the energy only appears on the moving target to be covered, so less jamming energy is needed. We analyzed the proposed jamming principle against GMTI using the tri-channel interference cancelling technique. Our simulation results verify our analyses and confirm its jamming effectiveness for SAR-GMTI.
2017, 6(4): 368-375.
High-resolution synthetic aperture radar presents a significant challenge to imaging algorithms and computing power.Slide spotlight is an important mode that has both high resolution and wide azimuth swath. Generally,in the slide spotlight mode,the performance of conventional frequency domain imaging algorithms degrades because of orbit curvature,the time-variant azimuth chirp rate,and other factors.We adopt the Back-Projection (BP) algorithm in this study to counteract this limitation.We also propose a CPU/GPU heterogeneous BP algorithm to deal with the high computing complexity O (N3) of the BP algorithm.This heterogeneous BP algorithm makes full use of computing resources and accelerates imaging progress,and the design of a scheduling thread improves the flexibility of the algorithm.
High-resolution synthetic aperture radar presents a significant challenge to imaging algorithms and computing power.Slide spotlight is an important mode that has both high resolution and wide azimuth swath. Generally,in the slide spotlight mode,the performance of conventional frequency domain imaging algorithms degrades because of orbit curvature,the time-variant azimuth chirp rate,and other factors.We adopt the Back-Projection (BP) algorithm in this study to counteract this limitation.We also propose a CPU/GPU heterogeneous BP algorithm to deal with the high computing complexity O (N3) of the BP algorithm.This heterogeneous BP algorithm makes full use of computing resources and accelerates imaging progress,and the design of a scheduling thread improves the flexibility of the algorithm.
2017, 6(4): 376-387.
This study presents a novel processing scheme for Multiple-Input Multiple-Output (MIMO) Synthetic Aperture Radar (SAR) system with Short-Term Shift-Orthogonal (STSO) chirp waveforms to enhance its high-resolution wide-swath mapping capability. Taking advantage of multi-beam digital beamforming techniques in elevation, the STSO chirp waveforms can be efficiently separated from mixed echo signals. According to the geometry model and the antenna architecture of MIMO SAR system, the modified multichannel reconstruction matrix is used to reconstruct the separated signals in azimuth. In addition, the reconstruction data can be imaged via conventional SAR algorithm. Simulation experiments are conducted on both point targets and distributed targets, the results of which indicate that the proposed scheme can effectively suppress the mutual interferences between the STSO waveforms and that it has good imaging performance.
This study presents a novel processing scheme for Multiple-Input Multiple-Output (MIMO) Synthetic Aperture Radar (SAR) system with Short-Term Shift-Orthogonal (STSO) chirp waveforms to enhance its high-resolution wide-swath mapping capability. Taking advantage of multi-beam digital beamforming techniques in elevation, the STSO chirp waveforms can be efficiently separated from mixed echo signals. According to the geometry model and the antenna architecture of MIMO SAR system, the modified multichannel reconstruction matrix is used to reconstruct the separated signals in azimuth. In addition, the reconstruction data can be imaged via conventional SAR algorithm. Simulation experiments are conducted on both point targets and distributed targets, the results of which indicate that the proposed scheme can effectively suppress the mutual interferences between the STSO waveforms and that it has good imaging performance.
2017, 6(4): 388-396.
In bistatic spaceborne High-Resolution Wide-Swath SAR systems (HRWS-SAR), the azimuth reconstruction to obtain a uniform sampling signal or Doppler spectrum is a crucial step in image processing because azimuth signals are generally of non-uniform sampling type. In this study, the variant transmitting distance to receiving distance radio is approximated to be a constant, the equivalence between the bistatic and monostatic SAR azimuth interchannel transfer functions is deduced, and the azimuth signal model in spaceborne HRWS-SAR with general bistatic configuration is established. Furthermore, the matrix inversion algorithm to reconstruct the azimuth signal is proposed; in addition, to measure the reconstruction performance, the formulae for the signal noise ratio scaling factor and the azimuth ambiguity signal ratio are provided. The azimuth reconstruction is simulated in several spaceborne HRWS-SAR systems with typical bistatic configuration, and the results show that the azimuth Doppler spectrum can be correctly reconstructed via the matrix inversion algorithm when the azimuth sampling is conducted without coinciding samples.
In bistatic spaceborne High-Resolution Wide-Swath SAR systems (HRWS-SAR), the azimuth reconstruction to obtain a uniform sampling signal or Doppler spectrum is a crucial step in image processing because azimuth signals are generally of non-uniform sampling type. In this study, the variant transmitting distance to receiving distance radio is approximated to be a constant, the equivalence between the bistatic and monostatic SAR azimuth interchannel transfer functions is deduced, and the azimuth signal model in spaceborne HRWS-SAR with general bistatic configuration is established. Furthermore, the matrix inversion algorithm to reconstruct the azimuth signal is proposed; in addition, to measure the reconstruction performance, the formulae for the signal noise ratio scaling factor and the azimuth ambiguity signal ratio are provided. The azimuth reconstruction is simulated in several spaceborne HRWS-SAR systems with typical bistatic configuration, and the results show that the azimuth Doppler spectrum can be correctly reconstructed via the matrix inversion algorithm when the azimuth sampling is conducted without coinciding samples.
2017, 6(4): 397-407.
An effective way to achieve High Resolution and Wide Swath (HRWS) imaging capability is the multi-channel technique in azimuth. Improved resolution and swath can dramatically increase the volume of echo data in the SAR system. However, the onboard data storage and data-transmission bandwidth are limited, so data compression technique is typically used to reduce the volume of echo data. To study the effect of raw data compression on the azimuth multi-channel SAR system, in this paper, we establish a multi-channel SAR signal model based on data compression. We then derive and analyze the effects of data compression on the Signal-to-Noise Ratio (SNR) scaling factor of the multi-channel SAR system and quantization noise. Finally, we verify the validity of the proposed model and analysis results using simulation and real data and discuss the effect of data compression on the Peek-to-Ghost Ratio (PGR). The results of this paper provide an important theoretical basis for the choice of compression method in the multi-channel SAR system.
An effective way to achieve High Resolution and Wide Swath (HRWS) imaging capability is the multi-channel technique in azimuth. Improved resolution and swath can dramatically increase the volume of echo data in the SAR system. However, the onboard data storage and data-transmission bandwidth are limited, so data compression technique is typically used to reduce the volume of echo data. To study the effect of raw data compression on the azimuth multi-channel SAR system, in this paper, we establish a multi-channel SAR signal model based on data compression. We then derive and analyze the effects of data compression on the Signal-to-Noise Ratio (SNR) scaling factor of the multi-channel SAR system and quantization noise. Finally, we verify the validity of the proposed model and analysis results using simulation and real data and discuss the effect of data compression on the Peek-to-Ghost Ratio (PGR). The results of this paper provide an important theoretical basis for the choice of compression method in the multi-channel SAR system.
2017, 6(4): 408-419.
To achieve high-resolution wide-swath imaging, the use of multichannel techniques in azimuth is effective for spaceborne Synthetic Aperture Radar (SAR). For azimuth multichannel systems, the signal in azimuth is nonuniformly sampled if the uniform sampling condition related to Pulse Repetition Frequency (PRF) is not satisfied, which makes it important to reconstruct the azimuth signal prior to image formation. In this study, to solve the azimuth signal reconstruction problem in multichannel SAR, we propose the innovative use of a multiframe super-resolution method in Digital Image Processing (DIP) and summarize the general multiframe super-resolution process. Our simulation results and real data experiments verify the effectiveness of the proposed method, which demonstrates some advantages in complexity performance. By establishing linkages between the problem of signal reconstruction of nonuniformly sampled signals and the multiframe super-resolution concept, we provide a new approach to this traditional signal reconstruction problem.
To achieve high-resolution wide-swath imaging, the use of multichannel techniques in azimuth is effective for spaceborne Synthetic Aperture Radar (SAR). For azimuth multichannel systems, the signal in azimuth is nonuniformly sampled if the uniform sampling condition related to Pulse Repetition Frequency (PRF) is not satisfied, which makes it important to reconstruct the azimuth signal prior to image formation. In this study, to solve the azimuth signal reconstruction problem in multichannel SAR, we propose the innovative use of a multiframe super-resolution method in Digital Image Processing (DIP) and summarize the general multiframe super-resolution process. Our simulation results and real data experiments verify the effectiveness of the proposed method, which demonstrates some advantages in complexity performance. By establishing linkages between the problem of signal reconstruction of nonuniformly sampled signals and the multiframe super-resolution concept, we provide a new approach to this traditional signal reconstruction problem.
Range Ambiguity Suppression Approach for Quad-pol SAR Systems Based on Modified Azimuth Phase Coding
2017, 6(4): 420-431.
For conventional quadrature-polarimetric (quad-pol) Synthetic Aperture Radar (SAR) systems, as cross-polarized (cross-pol) channels are influenced by the strong co-polarized (co-pol) range ambiguous returns, the range ambiguity levels of cross-polchannels are markedly reduced, which severely restricts the unambiguous swaths. A novel transmission scheme called a hybrid-polarimetric (hybrid-pol) mode is introduced to enhance the range ambiguity levels of cross-pol channels. This scheme improves the performance of cross-pol channels with regards to range ambiguity but deteriorates that of co-pol channels. Therefore, to further enhance the range ambiguity levels of quad-pol SAR systems, the Modified Azimuth Phase Coding (MAPC) technique based on hybrid-pol SAR systems is proposed in this study. By taking advantage of the MAPC modulation/demodulation, the power of range ambiguities is transferred to the azimuth that is filtered by an optimized Wiener filter in the Doppler domain. The simulation results validate that the MAPC technique can markedly eliminate the range ambiguity of quad-pol SAR systems and extend the unambiguous swaths.
For conventional quadrature-polarimetric (quad-pol) Synthetic Aperture Radar (SAR) systems, as cross-polarized (cross-pol) channels are influenced by the strong co-polarized (co-pol) range ambiguous returns, the range ambiguity levels of cross-polchannels are markedly reduced, which severely restricts the unambiguous swaths. A novel transmission scheme called a hybrid-polarimetric (hybrid-pol) mode is introduced to enhance the range ambiguity levels of cross-pol channels. This scheme improves the performance of cross-pol channels with regards to range ambiguity but deteriorates that of co-pol channels. Therefore, to further enhance the range ambiguity levels of quad-pol SAR systems, the Modified Azimuth Phase Coding (MAPC) technique based on hybrid-pol SAR systems is proposed in this study. By taking advantage of the MAPC modulation/demodulation, the power of range ambiguities is transferred to the azimuth that is filtered by an optimized Wiener filter in the Doppler domain. The simulation results validate that the MAPC technique can markedly eliminate the range ambiguity of quad-pol SAR systems and extend the unambiguous swaths.
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