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Editor Work2017 Vol. 6, No. 1
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2017, 6(1): 1-10.
Abstract
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Combining synthetic-aperture imaging and coherent-light detection technology, the weak signal identification capacity of Synthetic Aperture Ladar (SAL) reaches the photo level, and the image resolution exceeds the diffraction limit of the telescope to obtain high-resolution images irrespective to ranges. This paper introduces SAL, including the development path, technology characteristics, and the restriction of imaging swath. On the basis of this, we propose to integrate the SAL technology for extending its swath. By analyzing the scanning-operation mode and the signal model, the paper explicitly proposes that the former mode will be the developmental trend of the SAL technology. This paper also introduces the flight demonstrations of the SAL and the imaging results of remote targets, showing the potential of the SAL in long-range, high-resolution, and scanning-imaging applications. The technology and the theory of the scanning mode of SAL compensates for the defects related to the swath and operation efficiency of the current SAL. It provides scientific foundation for the SAL system applied in wide swath, high resolution earth observation, and the ISAL system applied in space-targets imaging.
Combining synthetic-aperture imaging and coherent-light detection technology, the weak signal identification capacity of Synthetic Aperture Ladar (SAL) reaches the photo level, and the image resolution exceeds the diffraction limit of the telescope to obtain high-resolution images irrespective to ranges. This paper introduces SAL, including the development path, technology characteristics, and the restriction of imaging swath. On the basis of this, we propose to integrate the SAL technology for extending its swath. By analyzing the scanning-operation mode and the signal model, the paper explicitly proposes that the former mode will be the developmental trend of the SAL technology. This paper also introduces the flight demonstrations of the SAL and the imaging results of remote targets, showing the potential of the SAL in long-range, high-resolution, and scanning-imaging applications. The technology and the theory of the scanning mode of SAL compensates for the defects related to the swath and operation efficiency of the current SAL. It provides scientific foundation for the SAL system applied in wide swath, high resolution earth observation, and the ISAL system applied in space-targets imaging.
2017, 6(1): 11-16.
GF-3, the first full-polarimetric Synthetic Aperture Radar (SAR) satellite of China with a resolution up to 1 m, was successfully launched in August 2016 and, after 5 months of in-orbit calibration, it was officially delivered to the users in January 2017. In this paper, the geometric positioning error sources of the entire system are analyzed based on the real data acquisition, including atmospheric transmission, image processing, and geometric positioning. The positioning precision of the SAR system is validated by corner reflectors. The results show that the satellite positioning accuracy improved by 3 m.
GF-3, the first full-polarimetric Synthetic Aperture Radar (SAR) satellite of China with a resolution up to 1 m, was successfully launched in August 2016 and, after 5 months of in-orbit calibration, it was officially delivered to the users in January 2017. In this paper, the geometric positioning error sources of the entire system are analyzed based on the real data acquisition, including atmospheric transmission, image processing, and geometric positioning. The positioning precision of the SAR system is validated by corner reflectors. The results show that the satellite positioning accuracy improved by 3 m.
2017, 6(1): 17-24.
Usually, in traditional Inverse Synthetic Aperture Radar (ISAR) systems design and mode selection for space satellite targets, coherent integration gain in azimuth direction hardly can be analyzed, which depends on target’s motion. In this study, we combine the target orbit parameters to determine its motion relative to radar and deduce coherent integration equation in ISAR imaging to realize the selection of imaging intervals based on coherent integration, which can ensure the resolution in azimuth direction. Meanwhile, we analyze the influence of target orbit altitude to echo power and imaging Signal-to-Noise Ratio (SNR) that provides a new indicator for space observation ISAR systems design. The result of simulation experiment illustrates that with target orbit altitude increasing, coherent integration gain in azimuth direction of large-angular observation offsets the decreasing of imaging SNR in a degree, which provides a brand-new perspective for space observation ISAR systems and signal processing design.
Usually, in traditional Inverse Synthetic Aperture Radar (ISAR) systems design and mode selection for space satellite targets, coherent integration gain in azimuth direction hardly can be analyzed, which depends on target’s motion. In this study, we combine the target orbit parameters to determine its motion relative to radar and deduce coherent integration equation in ISAR imaging to realize the selection of imaging intervals based on coherent integration, which can ensure the resolution in azimuth direction. Meanwhile, we analyze the influence of target orbit altitude to echo power and imaging Signal-to-Noise Ratio (SNR) that provides a new indicator for space observation ISAR systems design. The result of simulation experiment illustrates that with target orbit altitude increasing, coherent integration gain in azimuth direction of large-angular observation offsets the decreasing of imaging SNR in a degree, which provides a brand-new perspective for space observation ISAR systems and signal processing design.
2017, 6(1): 25-33.
Compressed Sensing (CS) has been proved to be effective in Synthetic Aperture Radar (SAR) imaging. Previous CS-SAR imaging algorithms are very time consuming, especially for producing high-resolution images. In this study, we propose a new CS-SAR imaging method based on the well-known omega-K algorithm, which is precise and convenient to use in SAR imaging. First, we derive an inverse omega-K algorithm to directly obtain echoes without any convolution between the transmitted signal and scene. Then, we formulate the SAR imaging problem into a sparse regularization problem and solve it using an iterative thresholding algorithm. With our derived inverse omega-K algorithm, we can save significant amounts of computation time and computer memory usage. Simulation results show that the proposed method can effectively recover SAR images with much less data than that required by the Nyquist rate.
Compressed Sensing (CS) has been proved to be effective in Synthetic Aperture Radar (SAR) imaging. Previous CS-SAR imaging algorithms are very time consuming, especially for producing high-resolution images. In this study, we propose a new CS-SAR imaging method based on the well-known omega-K algorithm, which is precise and convenient to use in SAR imaging. First, we derive an inverse omega-K algorithm to directly obtain echoes without any convolution between the transmitted signal and scene. Then, we formulate the SAR imaging problem into a sparse regularization problem and solve it using an iterative thresholding algorithm. With our derived inverse omega-K algorithm, we can save significant amounts of computation time and computer memory usage. Simulation results show that the proposed method can effectively recover SAR images with much less data than that required by the Nyquist rate.
2017, 6(1): 34-42.
Due to the Doppler Blind Zone (DBZ), the target tracking of Doppler radar becomes more and more complicated. In this paper, a multi-target tracking algorithm based on Gaussian Mixture Probability Hypothesis Density (GM-PHD) for DBZ is proposed. The algorithm introduces the Minimum Detectable Velocity (MDV) information to the traditional detection probability model to update the GM-PHD and the updated equation of the GM-PHD is deduced. The simulation results show that, compared to the traditional GM-PHD with the only Doppler measurement, the proposed algorithm improves greatly the radar tracking performance of moving target under the condition of minor MDV.
Due to the Doppler Blind Zone (DBZ), the target tracking of Doppler radar becomes more and more complicated. In this paper, a multi-target tracking algorithm based on Gaussian Mixture Probability Hypothesis Density (GM-PHD) for DBZ is proposed. The algorithm introduces the Minimum Detectable Velocity (MDV) information to the traditional detection probability model to update the GM-PHD and the updated equation of the GM-PHD is deduced. The simulation results show that, compared to the traditional GM-PHD with the only Doppler measurement, the proposed algorithm improves greatly the radar tracking performance of moving target under the condition of minor MDV.
2017, 6(1): 43-54.
A Multiple-Input Multiple-Output (MIMO) ultra-wideband radar can detect the range and azimuth information of targets in real time. It is widely used for geological surveys, life rescue, through-wall tracking, and other military or civil fields. This paper presents the design of an ultra-wideband pseudo random coded MIMO radar that is based on Radio Frequency (RF) switches and implements a MIMO radar system. RF switches are employed to reduce cost and complexity of the system. As the switch pressure value is limited, the peak power of the transmitting signal is 18 dBm. The ultra-wideband radar echo is obtained by hybrid sampling, and pulse compression is computed by Digital Signal Processors (DSPs) embedded in an Field-Programmable Gate Array (FPGA) to simplify the signal process. The experiment illustrates that the radar system can detect the range and azimuth information of targets in real time.
A Multiple-Input Multiple-Output (MIMO) ultra-wideband radar can detect the range and azimuth information of targets in real time. It is widely used for geological surveys, life rescue, through-wall tracking, and other military or civil fields. This paper presents the design of an ultra-wideband pseudo random coded MIMO radar that is based on Radio Frequency (RF) switches and implements a MIMO radar system. RF switches are employed to reduce cost and complexity of the system. As the switch pressure value is limited, the peak power of the transmitting signal is 18 dBm. The ultra-wideband radar echo is obtained by hybrid sampling, and pulse compression is computed by Digital Signal Processors (DSPs) embedded in an Field-Programmable Gate Array (FPGA) to simplify the signal process. The experiment illustrates that the radar system can detect the range and azimuth information of targets in real time.
2017, 6(1): 55-64.
The distributed aperture coherence-synthetic radar could accomplish long-range and high-precision detection performance according to include multi-unit radars and energy synthesize in space. It provides an effective measurement to resolve the contradiction between platform restriction and detection performance. As the new radar has many advantages, such as strong survival ability, high cost-effectiveness ratio, high angular accuracy, strong expandability, and easy realization, it significantly orients the development of radars. In this paper, the operating principle, technical advantage, development of domestic and foreign, and the key technology of the distributed aperture coherence-synthetic radar are illustrated; in particular, the principle verification experiments are also described. Lastly, the future perspective for the development and typical application of this new radar is also discussed.
The distributed aperture coherence-synthetic radar could accomplish long-range and high-precision detection performance according to include multi-unit radars and energy synthesize in space. It provides an effective measurement to resolve the contradiction between platform restriction and detection performance. As the new radar has many advantages, such as strong survival ability, high cost-effectiveness ratio, high angular accuracy, strong expandability, and easy realization, it significantly orients the development of radars. In this paper, the operating principle, technical advantage, development of domestic and foreign, and the key technology of the distributed aperture coherence-synthetic radar are illustrated; in particular, the principle verification experiments are also described. Lastly, the future perspective for the development and typical application of this new radar is also discussed.
2017, 6(1): 65-72.
Digital broadcasting and television are important classes of illuminators of opportunity for passive radars. Distributed and multistatic structure are the development trends for passive radars. Most modern digital broadcasting and television systems work on a network, which not only provides a natural condition to distributed passive radar but also puts forward higher requirements on the design of passive radar systems. Among those requirements, precise synchronization among the receivers and transmitters as well as among multiple receiving stations, which mainly involves frequency and time synchronization, is the first to be solved. To satisfy the synchronization requirements of distributed passive radars, a synchronization scheme based on GPS is presented in this paper. Moreover, an effective scheme based on the China Mobile Multimedia Broadcasting signal is proposed to test the system synchronization performance. Finally, the reliability of the synchronization design is verified via the distributed multistatic passive radar experiments.
Digital broadcasting and television are important classes of illuminators of opportunity for passive radars. Distributed and multistatic structure are the development trends for passive radars. Most modern digital broadcasting and television systems work on a network, which not only provides a natural condition to distributed passive radar but also puts forward higher requirements on the design of passive radar systems. Among those requirements, precise synchronization among the receivers and transmitters as well as among multiple receiving stations, which mainly involves frequency and time synchronization, is the first to be solved. To satisfy the synchronization requirements of distributed passive radars, a synchronization scheme based on GPS is presented in this paper. Moreover, an effective scheme based on the China Mobile Multimedia Broadcasting signal is proposed to test the system synchronization performance. Finally, the reliability of the synchronization design is verified via the distributed multistatic passive radar experiments.
2017, 6(1): 73-80.
Only a subset of transmitters and receivers in a distributed Multi-Input Multi-Output (MIMO) radar network is allowed to actively track a target at a particular instance due to the limited time and energy resource of a MIMO radar network. It is therefore desirable to obtain an efficient method to overcome the resource constraints while optimizing the tracking performance. In this study, posterior Cramer-Rao lower bound is used as the performance metric and the selection problem is formulated as a Boolean programming problem aiming at optimizing the worst tracking performance of multiple targets. It is later relaxed to a semidefinite programming and solved by the block coordinate descend method. Numerical results show that proposed method superior to the fixed selection method. In addition, with less computation complexity, the proposed method obtains nearly equivalent performance compared with exhaustive search method.
Only a subset of transmitters and receivers in a distributed Multi-Input Multi-Output (MIMO) radar network is allowed to actively track a target at a particular instance due to the limited time and energy resource of a MIMO radar network. It is therefore desirable to obtain an efficient method to overcome the resource constraints while optimizing the tracking performance. In this study, posterior Cramer-Rao lower bound is used as the performance metric and the selection problem is formulated as a Boolean programming problem aiming at optimizing the worst tracking performance of multiple targets. It is later relaxed to a semidefinite programming and solved by the block coordinate descend method. Numerical results show that proposed method superior to the fixed selection method. In addition, with less computation complexity, the proposed method obtains nearly equivalent performance compared with exhaustive search method.
2017, 6(1): 81-89.
To address the problem of target detection in distributed MIMO radar, three styles of distributed MIMO radar systems are given in this paper. With respect to the geometric distribution relations of distributed MIMO radar, the styles are distributed coherent MIMO radar, random phase MIMO radar, and random amplitude-phase MIMO radar. Next, the square law detector structures of random phase and random amplitude-phase MIMO radar are derived in the paper when there is a low signal-to-noise ratio, and the performance of the two detectors are analyzed as well. Finally, simulation results demonstrate the theoretical analysis of this paper are of guiding significance for the actual engineering.
To address the problem of target detection in distributed MIMO radar, three styles of distributed MIMO radar systems are given in this paper. With respect to the geometric distribution relations of distributed MIMO radar, the styles are distributed coherent MIMO radar, random phase MIMO radar, and random amplitude-phase MIMO radar. Next, the square law detector structures of random phase and random amplitude-phase MIMO radar are derived in the paper when there is a low signal-to-noise ratio, and the performance of the two detectors are analyzed as well. Finally, simulation results demonstrate the theoretical analysis of this paper are of guiding significance for the actual engineering.
2017, 6(1): 90-97.
The fast fluctuation associated with maneuvering a target's radar cross-section often affects the imaging performance stability of traditional monostatic Inverse Synthetic Aperture Radar (ISAR). To address this problem, in this study, we propose an imaging method based on the fusion of sub-images of frequencydiversity-distributed multiple Input-Multiple Output-Inverse Synthetic Aperture Radar (MIMO-ISAR). First, we establish the analytic expression of a two-dimensional ISAR sub-image acquired by different channels of distributed MIMO-ISAR. Then, we derive the distance and azimuth distortion factors of the image acquired by the different channels. By compensating for the distortion of the ISAR image, we ultimately realize distributed MIMO-ISAR fusion imaging. Simulations verify the validity of this imaging method using distributed MIMOISAR.
The fast fluctuation associated with maneuvering a target's radar cross-section often affects the imaging performance stability of traditional monostatic Inverse Synthetic Aperture Radar (ISAR). To address this problem, in this study, we propose an imaging method based on the fusion of sub-images of frequencydiversity-distributed multiple Input-Multiple Output-Inverse Synthetic Aperture Radar (MIMO-ISAR). First, we establish the analytic expression of a two-dimensional ISAR sub-image acquired by different channels of distributed MIMO-ISAR. Then, we derive the distance and azimuth distortion factors of the image acquired by the different channels. By compensating for the distortion of the ISAR image, we ultimately realize distributed MIMO-ISAR fusion imaging. Simulations verify the validity of this imaging method using distributed MIMOISAR.
2017, 6(1): 98-105.
Micro-motion is a crucial feature used in ballistic target recognition. To address the problem that single-view observations cannot extract true micro-motion parameters, we propose a novel algorithm based on the narrowband radar network to extract three-dimensional precession features. First, we construct a precession model of the cone-shaped target, and as a precondition, we consider the invisible problem of scattering centers. We then analyze in detail the micro-Doppler modulation trait caused by the precession. Then, we match each scattering center in different perspectives based on the ratio of the top scattering center's micro-Doppler frequency modulation coefficient and extract the 3D coning vector of the target by establishing associated multi-aspect equation systems. In addition, we estimate feature parameters by utilizing the correlation of the micro-Doppler frequency modulation coefficient of the three scattering centers combined with the frequency compensation method. We then calculate the coordinates of the conical point in each moment and reconstruct the 3D spatial portion. Finally, we provide simulation results to validate the proposed algorithm.
Micro-motion is a crucial feature used in ballistic target recognition. To address the problem that single-view observations cannot extract true micro-motion parameters, we propose a novel algorithm based on the narrowband radar network to extract three-dimensional precession features. First, we construct a precession model of the cone-shaped target, and as a precondition, we consider the invisible problem of scattering centers. We then analyze in detail the micro-Doppler modulation trait caused by the precession. Then, we match each scattering center in different perspectives based on the ratio of the top scattering center's micro-Doppler frequency modulation coefficient and extract the 3D coning vector of the target by establishing associated multi-aspect equation systems. In addition, we estimate feature parameters by utilizing the correlation of the micro-Doppler frequency modulation coefficient of the three scattering centers combined with the frequency compensation method. We then calculate the coordinates of the conical point in each moment and reconstruct the 3D spatial portion. Finally, we provide simulation results to validate the proposed algorithm.
2017, 6(1): 106-113.
In this paper, we study the clutter suppression problem of an airborne bistatic radar with range ambiguity and propose a novel method to reduce the impact of range ambiguity using geometric configuration. First, a clutter model, under any bistatic configuration is used to analyze the impact of range ambiguity. Second, a clutter equal-distance ring model of the airborne bistatic radar is established, and the relation between the geometric configuration and range ambiguity is analyzed. Third, the maximum pulse repetition frequency required to avoid range ambiguity is calculated. Simulation results show that the clutter suppression performance of an airborne bistatic STAP is greatly diminished with range ambiguity; however, this impact can effectively be reduced by selecting the appropriate radar configuration. Finally, simulation is performed to validate tests its validity.
In this paper, we study the clutter suppression problem of an airborne bistatic radar with range ambiguity and propose a novel method to reduce the impact of range ambiguity using geometric configuration. First, a clutter model, under any bistatic configuration is used to analyze the impact of range ambiguity. Second, a clutter equal-distance ring model of the airborne bistatic radar is established, and the relation between the geometric configuration and range ambiguity is analyzed. Third, the maximum pulse repetition frequency required to avoid range ambiguity is calculated. Simulation results show that the clutter suppression performance of an airborne bistatic STAP is greatly diminished with range ambiguity; however, this impact can effectively be reduced by selecting the appropriate radar configuration. Finally, simulation is performed to validate tests its validity.
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