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The technique of radar feature extraction, imaging, and recognition of target with micro-motions has become one of the most potential research directions in the field of radar target accurate recognition. In this paper, the concept of micro-motion is first introduced briefly. Subsequently, the achievements of echo modeling, feature extraction, imaging, and identification of micro-motion targets are summarized. Several typical frontier applications are then introduced. Finally, the future development trends of the research are discussed. The technique of radar feature extraction, imaging, and recognition of target with micro-motions has become one of the most potential research directions in the field of radar target accurate recognition. In this paper, the concept of micro-motion is first introduced briefly. Subsequently, the achievements of echo modeling, feature extraction, imaging, and identification of micro-motion targets are summarized. Several typical frontier applications are then introduced. Finally, the future development trends of the research are discussed.
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Deep learning such as deep neural networks has revolutionized the computer vision area. Deep learning-based algorithms have surpassed conventional algorithms in terms of performance by a significant margin. This paper reviews our works in the application of deep convolutional neural networks to target recognition and terrain classification using the SAR image. A convolutional neural network is employed to automatically extract a hierarchic feature representation from the data, based on which the target recognition and terrain classification can be conducted. Experimental results on the MSTAR benchmark dataset reveal that deep convolutional network could achieve a state-of-the-art classification accuracy of 99% for the 10-class task. For a polarimetric SAR image classification, we propose complex-valued convolutional neural networks for complex SAR images. This algorithm achieved a state-of-the-art accuracy of 95% for the 15-class task on the Flevoland benchmark dataset. Deep learning such as deep neural networks has revolutionized the computer vision area. Deep learning-based algorithms have surpassed conventional algorithms in terms of performance by a significant margin. This paper reviews our works in the application of deep convolutional neural networks to target recognition and terrain classification using the SAR image. A convolutional neural network is employed to automatically extract a hierarchic feature representation from the data, based on which the target recognition and terrain classification can be conducted. Experimental results on the MSTAR benchmark dataset reveal that deep convolutional network could achieve a state-of-the-art classification accuracy of 99% for the 10-class task. For a polarimetric SAR image classification, we propose complex-valued convolutional neural networks for complex SAR images. This algorithm achieved a state-of-the-art accuracy of 95% for the 15-class task on the Flevoland benchmark dataset.
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Knowledge of target polarization characteristics is valuable for radar target detection, classification, and identification.We conducted experimental research on an Unmanned Aerial Vehicle (UAV) with complex materials and structures to determine the differences in polarimetric scattering between the UAV and its perfect electric conductor model.To illustrate the coherence of the entire UAV and its components using polarimetric scattering, we measured and analyzed each part.The results reveal that the airframe and aerofoils directly influence the depolarization, and that the polarimetric scattering characteristics of the airframe represent the primary source for the whole UAV. Knowledge of target polarization characteristics is valuable for radar target detection, classification, and identification.We conducted experimental research on an Unmanned Aerial Vehicle (UAV) with complex materials and structures to determine the differences in polarimetric scattering between the UAV and its perfect electric conductor model.To illustrate the coherence of the entire UAV and its components using polarimetric scattering, we measured and analyzed each part.The results reveal that the airframe and aerofoils directly influence the depolarization, and that the polarimetric scattering characteristics of the airframe represent the primary source for the whole UAV.
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Spaceborne SAR, which is a kind of initiatively microwave imaging sensor, plays an important role in gathering information with its capability of all-day and all-weather imaging, and has become an indispensable sensor for observing the earth. With the development of SAR techniques, Spaceborne SAR has been provided with the ability of High-Resolution Wide-Swath, miniaturization with low cost, bistatic and multi-mode imaging, and Ground Moving Target Indicating (GMTI), so more accurate information about the culture could be obtained with lower cost. In the meantime, more technique problems with muliti-mode, new work system and complex environment are arising and needed to be solved. The main work of this paper is discussing the current situation and the future development of Spaceborne SAR. Spaceborne SAR, which is a kind of initiatively microwave imaging sensor, plays an important role in gathering information with its capability of all-day and all-weather imaging, and has become an indispensable sensor for observing the earth. With the development of SAR techniques, Spaceborne SAR has been provided with the ability of High-Resolution Wide-Swath, miniaturization with low cost, bistatic and multi-mode imaging, and Ground Moving Target Indicating (GMTI), so more accurate information about the culture could be obtained with lower cost. In the meantime, more technique problems with muliti-mode, new work system and complex environment are arising and needed to be solved. The main work of this paper is discussing the current situation and the future development of Spaceborne SAR.
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Progress in Circular SAR Imaging Technique
Hong Wen
2012, 1(2): 124-135. 2012, 1(2): 124-135.
Abstract(2848)
13765KB(3359)
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.
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Viewing from the interaction between external and internal causes on the time scale of history, present and future, this paper analyzes and demonstrates the developing motivation and stage characteristics of radar technology. The external causes are interpreted as target, environment and mission, and the internal causes as information acquisition pattern, realization ability and resource utilization. The fundamental law of radar development is revealed as evolving stepwise from lower into higher dimension of detection through the aromorphosis of channel configuration, viewing angle and signal dimensionality, while the main innovation strategies of radar technology are summarized as modifying information acquisition pattern, enhancing realization ability and increasing utilized resources. Furthermore, the developing trends and main characteristics of future radar technology are deduced, and proposals for promoting future innovation and development are also presented. Viewing from the interaction between external and internal causes on the time scale of history, present and future, this paper analyzes and demonstrates the developing motivation and stage characteristics of radar technology. The external causes are interpreted as target, environment and mission, and the internal causes as information acquisition pattern, realization ability and resource utilization. The fundamental law of radar development is revealed as evolving stepwise from lower into higher dimension of detection through the aromorphosis of channel configuration, viewing angle and signal dimensionality, while the main innovation strategies of radar technology are summarized as modifying information acquisition pattern, enhancing realization ability and increasing utilized resources. Furthermore, the developing trends and main characteristics of future radar technology are deduced, and proposals for promoting future innovation and development are also presented.
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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.
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This paper first reviews the history and trends in the development of spaceborne Synthetic Aperture Radar (SAR) satellite technology in the USA and Europe. The basic information regarding launched satellites and future satellite plans are introduced. Then, this paper summarizes and categorizes the imaging algorithms of spaceborn SAR satellites, and analyzes the advantages and disadvantages of each algorithm. Next, the scope and the application status of each algorithm are presented. Then, the paper presents details of trends related to the SAR imaging algorithm, which mainly introduces the algorithms based on compressive sensing theory and new image modes. The simulation results are also presented. Finally, we summarize the development direction of the spaceborne SAR imaging algorithm. This paper first reviews the history and trends in the development of spaceborne Synthetic Aperture Radar (SAR) satellite technology in the USA and Europe. The basic information regarding launched satellites and future satellite plans are introduced. Then, this paper summarizes and categorizes the imaging algorithms of spaceborn SAR satellites, and analyzes the advantages and disadvantages of each algorithm. Next, the scope and the application status of each algorithm are presented. Then, the paper presents details of trends related to the SAR imaging algorithm, which mainly introduces the algorithms based on compressive sensing theory and new image modes. The simulation results are also presented. Finally, we summarize the development direction of the spaceborne SAR imaging algorithm.
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Collision avoidance radar for trains is pregnant for safety transportation. In order to realize low cost and high performance of azimuth accuracy, we have developed MMW (Milli-Meter Wave) radar, which employs switched phased array and frequency stepped technology. This paper analyses the radiation patterns of transmitting/receiving antennas and compensation method for amplitude/phase errors of synthetic wideband frequency stepped signal. To confirm the operation of the radar, low cost millimeter-wave collision avoidance radar was fabricated. Lots of experiments confirmed a high azimuth and range resolution. Collision avoidance radar for trains is pregnant for safety transportation. In order to realize low cost and high performance of azimuth accuracy, we have developed MMW (Milli-Meter Wave) radar, which employs switched phased array and frequency stepped technology. This paper analyses the radiation patterns of transmitting/receiving antennas and compensation method for amplitude/phase errors of synthetic wideband frequency stepped signal. To confirm the operation of the radar, low cost millimeter-wave collision avoidance radar was fabricated. Lots of experiments confirmed a high azimuth and range resolution.
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Recently, a novel conception of Synthetic Aperture Radar (SAR) based on Multi-Input Multi-Output (MIMO) technology draws much attention for its potential advantages. MIMO-SAR could obtain much more equivalent channels than the number of the physical array elements by simultaneously utilizing multiple antennas at transmission and reception. These additional channels are demonstrated to be useful for the application of High-Resolution Wide-Swath (HRWS) imaging and slowly moving target indication. In this paper, a detailed discussion on the conception and connotation of MIMO-SAR is made firstly, and then the investigation states of MIMO-SAR, such as high range resolution SAR imaging, three-dimensional down-looking SAR imaging, HRWS imaging and Ground Moving Target Indication (GMTI), are discussed. Base on the discussion mentioned above, the advantages and disadvantages of MIMO-SAR system are analyzed, and the key technical issues in MIMO-SAR are summarized. At last, the prospects of MIMO-SAR application are pointed out. Recently, a novel conception of Synthetic Aperture Radar (SAR) based on Multi-Input Multi-Output (MIMO) technology draws much attention for its potential advantages. MIMO-SAR could obtain much more equivalent channels than the number of the physical array elements by simultaneously utilizing multiple antennas at transmission and reception. These additional channels are demonstrated to be useful for the application of High-Resolution Wide-Swath (HRWS) imaging and slowly moving target indication. In this paper, a detailed discussion on the conception and connotation of MIMO-SAR is made firstly, and then the investigation states of MIMO-SAR, such as high range resolution SAR imaging, three-dimensional down-looking SAR imaging, HRWS imaging and Ground Moving Target Indication (GMTI), are discussed. Base on the discussion mentioned above, the advantages and disadvantages of MIMO-SAR system are analyzed, and the key technical issues in MIMO-SAR are summarized. At last, the prospects of MIMO-SAR application are pointed out.
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This paper gives the experimental research of HF Passive Bistatic Radar (HFPBR) based on Digital Radio Mondiale (DRM) digital AM broadcasting that have been first carried out in China, using the newly-developed all-digital active/passive integrated HF surface wave radar system. The principle, key techniques, experimental equipment, and preliminary results are introduced about this new radar system. Based on analysis of the measurement data, experimental results under different scenarios including surface-wave, sky-wave, and hybrid sky-surface propagation modes are presented, which have proved, for the first time worldwide, the technical feasibility of using DRM broadcasting signal for over-the-horizon detection by field experiment and formed the theoretical and experimental basis for the further development of HFPBR. This paper gives the experimental research of HF Passive Bistatic Radar (HFPBR) based on Digital Radio Mondiale (DRM) digital AM broadcasting that have been first carried out in China, using the newly-developed all-digital active/passive integrated HF surface wave radar system. The principle, key techniques, experimental equipment, and preliminary results are introduced about this new radar system. Based on analysis of the measurement data, experimental results under different scenarios including surface-wave, sky-wave, and hybrid sky-surface propagation modes are presented, which have proved, for the first time worldwide, the technical feasibility of using DRM broadcasting signal for over-the-horizon detection by field experiment and formed the theoretical and experimental basis for the further development of HFPBR.
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As a new radar technology, the distributed aperture coherent radar is expected to be the next generation radar, which is easier to transport and less expensive than the traditional large aperture radar. However, the time synchronization and phase synchronization are key issues to be addressed for the distributed aperture coherent radar. In this paper, the error sources of time synchronization and phase synchronization are analyzed, and the corresponding mathematical models are first derived. Then, the impact of synchronization errors on the coherent performance is simulated, and the accuracy of time and phase synchronization is presented based on the simulation results. Finally, the noncorrelation transmission scheme and the calibration scheme based on the wired transmission are proposed to realize the time and phase synchronization, respectively. Research of the synchronization problem could be very helpful to realize the new radar technology of distributed aperture coherent radar. As a new radar technology, the distributed aperture coherent radar is expected to be the next generation radar, which is easier to transport and less expensive than the traditional large aperture radar. However, the time synchronization and phase synchronization are key issues to be addressed for the distributed aperture coherent radar. In this paper, the error sources of time synchronization and phase synchronization are analyzed, and the corresponding mathematical models are first derived. Then, the impact of synchronization errors on the coherent performance is simulated, and the accuracy of time and phase synchronization is presented based on the simulation results. Finally, the noncorrelation transmission scheme and the calibration scheme based on the wired transmission are proposed to realize the time and phase synchronization, respectively. Research of the synchronization problem could be very helpful to realize the new radar technology of distributed aperture coherent radar.
13
Based on the recently developed active-passive multifunctional all-digital HF surface wave radar hardware platform of Wuhan University, an experiment study of integrated technology for shortwave communication and Over-The-Horizon Radar (OTHR) application is carried out. Firstly, from the point of communication are demonstrated the key technologies of orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) in the short-wave communication. Secondly, from the point of radar detection are analyzed OFDM parameters design guidelines and its impact on the over-the-horizon radar detection performance. After the description of some key technologies related to communication signal demodulation and radar signal processing, the configuration parameters of hardware platform and experimental results are provided. The results show that the OFDM wave is done well in radar-communication integration systems, which is of great significance on the netted OTHR detection research. Based on the recently developed active-passive multifunctional all-digital HF surface wave radar hardware platform of Wuhan University, an experiment study of integrated technology for shortwave communication and Over-The-Horizon Radar (OTHR) application is carried out. Firstly, from the point of communication are demonstrated the key technologies of orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) in the short-wave communication. Secondly, from the point of radar detection are analyzed OFDM parameters design guidelines and its impact on the over-the-horizon radar detection performance. After the description of some key technologies related to communication signal demodulation and radar signal processing, the configuration parameters of hardware platform and experimental results are provided. The results show that the OFDM wave is done well in radar-communication integration systems, which is of great significance on the netted OTHR detection research.
14
Blind zones and ambiguities in range and velocity measurement are two important issues in traditional pulse-Doppler radar. By generating random deviations with respect to a mean Pulse Repetition Interval (PRI), this paper proposes a novel algorithm of Moving Target Detection (MTD) based on the Compressed Sensing (CS) theory, in which the random deviations of the PRIare converted to the Restricted Isometry Property (RIP) of the observing matrix. The ambiguities of range and velocity are eliminated by designing the signal parameters. The simulation results demonstrate that this scheme has high performance of detection, and there is no ambiguity and blind zones as well. It can also shorten the coherent processing interval compared to traditional staggered PRI mode because only one pulse train is needed instead of several trains. Blind zones and ambiguities in range and velocity measurement are two important issues in traditional pulse-Doppler radar. By generating random deviations with respect to a mean Pulse Repetition Interval (PRI), this paper proposes a novel algorithm of Moving Target Detection (MTD) based on the Compressed Sensing (CS) theory, in which the random deviations of the PRIare converted to the Restricted Isometry Property (RIP) of the observing matrix. The ambiguities of range and velocity are eliminated by designing the signal parameters. The simulation results demonstrate that this scheme has high performance of detection, and there is no ambiguity and blind zones as well. It can also shorten the coherent processing interval compared to traditional staggered PRI mode because only one pulse train is needed instead of several trains.
15
The antenna pattern uncertainty is the main error of SAR system. The technique for inflight antenna pattern measurement of spaceborne SAR is one of the most important technique of SAR calibration. This paper discusses the development courses of the inflight antenna pattern measurement of spaceborne SAR, analyses its development trend and compares the main inflight antenna pattern measurement techniques. This paper will be an important reference for designing a project of inflight antenna pattern measurement of spaceborne SAR. The antenna pattern uncertainty is the main error of SAR system. The technique for inflight antenna pattern measurement of spaceborne SAR is one of the most important technique of SAR calibration. This paper discusses the development courses of the inflight antenna pattern measurement of spaceborne SAR, analyses its development trend and compares the main inflight antenna pattern measurement techniques. This paper will be an important reference for designing a project of inflight antenna pattern measurement of spaceborne SAR.
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Conventional Frequency Scaling (FS) algorithm is applied to process Frequency Modulated Continuous Wave (FMCW) SAR, which will lead a heavy range frequency aliasing. Through analyzing basic principle of the FS algorithm and combining the scaling propertation of the Fourier transform, with the presence of a constant factor, this paper proposed a improved frequency scaling algorithm for range anti-aliasing. The proposed algorithm holds performance of the conventation one and just removes the aliasing. The successfully imaging a point target shows the validity of the proposed method. Conventional Frequency Scaling (FS) algorithm is applied to process Frequency Modulated Continuous Wave (FMCW) SAR, which will lead a heavy range frequency aliasing. Through analyzing basic principle of the FS algorithm and combining the scaling propertation of the Fourier transform, with the presence of a constant factor, this paper proposed a improved frequency scaling algorithm for range anti-aliasing. The proposed algorithm holds performance of the conventation one and just removes the aliasing. The successfully imaging a point target shows the validity of the proposed method.
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WiFi (Wireless Fidelity) is widely deployed all the world. When it is utilized as external illuminaor in Passive Radar, its broadband singal make the high resolution of detection be obtained in both the range and Doppler domains. In this paper, the typical WiFi signal format and its characters are analyzed, then the theoretical signal model is setup. Based on the theory of bistatic passive radar, the relationship between typical IEEE 802.11 signals format and the characters of its Ambiguity Function (AF) is analyzed. Moreover, the position and amplitude of side peaks in time and frequency domain is analyzed and its causes from the signal structure is also discussed. In this paper, a method for suppressing the side peaks based on the correction of direct-path reference signal is proposed, therefore to avoid the false alarm brought in target detection caused by side peak interference. Experimental results valid the proposed signal processing method. WiFi (Wireless Fidelity) is widely deployed all the world. When it is utilized as external illuminaor in Passive Radar, its broadband singal make the high resolution of detection be obtained in both the range and Doppler domains. In this paper, the typical WiFi signal format and its characters are analyzed, then the theoretical signal model is setup. Based on the theory of bistatic passive radar, the relationship between typical IEEE 802.11 signals format and the characters of its Ambiguity Function (AF) is analyzed. Moreover, the position and amplitude of side peaks in time and frequency domain is analyzed and its causes from the signal structure is also discussed. In this paper, a method for suppressing the side peaks based on the correction of direct-path reference signal is proposed, therefore to avoid the false alarm brought in target detection caused by side peak interference. Experimental results valid the proposed signal processing method.
18
Global Navigation Satellite System (GNSS), has a significant impact on all areas of human activity, not only can provide users with shared global navigation, position and timing information, but also can provide a L-band microwave signal source of long term stability and high temporal-spatial resolution. In recent years, development of the navigation satellite remote sensing applications using GNSS as a external illuminator, it has been forming a new Global Navigation Satellite System METeorology (GNSS/MET), of which Global Navigation Satellite System-Reflection (GNSS-R) signals remote sensing technology is rising. It could be considered as a non-cooperative artificial illuminator, bistatic (multi-static) radar system, and has the advantages of both passive and active remote sensing. Then it gets more and more peoples attention and favor, and broadening into Atmosphere -ocean and land surface remote sensing fields. However, the address of this technology is very messy at home and abroad, and not able to accurately express its special meaning. This article attempts to give a new term: Exogenous-Aided Remote Sensing (EARS) for discussion. Global Navigation Satellite System (GNSS), has a significant impact on all areas of human activity, not only can provide users with shared global navigation, position and timing information, but also can provide a L-band microwave signal source of long term stability and high temporal-spatial resolution. In recent years, development of the navigation satellite remote sensing applications using GNSS as a external illuminator, it has been forming a new Global Navigation Satellite System METeorology (GNSS/MET), of which Global Navigation Satellite System-Reflection (GNSS-R) signals remote sensing technology is rising. It could be considered as a non-cooperative artificial illuminator, bistatic (multi-static) radar system, and has the advantages of both passive and active remote sensing. Then it gets more and more peoples attention and favor, and broadening into Atmosphere -ocean and land surface remote sensing fields. However, the address of this technology is very messy at home and abroad, and not able to accurately express its special meaning. This article attempts to give a new term: Exogenous-Aided Remote Sensing (EARS) for discussion.
19
GEOsynchronous Circular SAR (GEOCSAR), having a high orbit, operating in a slant ellipse, and imaging in spherical surface, should be newly modeled to assess the resolution performance. In this paper, starting from modeling geometry, a function of slant range difference and orientation angle is deduced. Then we can obtain the three dimensional point spread function and make a conclusion of resolution affected by both sinc function and bessel function of first kind. Lastly, resolution with the variation of location of target, bandwidth, radius of orbit, and integral time is analyzed detailedly. Finally raw signal simulations show the validity of theoretical model. GEOsynchronous Circular SAR (GEOCSAR), having a high orbit, operating in a slant ellipse, and imaging in spherical surface, should be newly modeled to assess the resolution performance. In this paper, starting from modeling geometry, a function of slant range difference and orientation angle is deduced. Then we can obtain the three dimensional point spread function and make a conclusion of resolution affected by both sinc function and bessel function of first kind. Lastly, resolution with the variation of location of target, bandwidth, radius of orbit, and integral time is analyzed detailedly. Finally raw signal simulations show the validity of theoretical model.
20
According to analysis of separating the mixed echo by suppressing the cross-correlation noise in dual-input and dual-output SAR system, a new method based on threshold filter and inverse filter was proposed. The method can eliminate the most energy of cross-correlation noise by threshold filter, which can suppress the cross-correlation noise well. The principle and implementation steps are presented in detail. The computer simulation and account for the integrated sidelobe ratio showed the effectiveness of the proposed method. According to analysis of separating the mixed echo by suppressing the cross-correlation noise in dual-input and dual-output SAR system, a new method based on threshold filter and inverse filter was proposed. The method can eliminate the most energy of cross-correlation noise by threshold filter, which can suppress the cross-correlation noise well. The principle and implementation steps are presented in detail. The computer simulation and account for the integrated sidelobe ratio showed the effectiveness of the proposed method.
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