To detect highly maneuvering radar targets in low signal-to-noise ratio conditions, a hybrid long-time integration method is proposed, which combines Radon-Fourier Transform(RFT), Dynamic Programming(DP), and Binary I...To detect highly maneuvering radar targets in low signal-to-noise ratio conditions, a hybrid long-time integration method is proposed, which combines Radon-Fourier Transform(RFT), Dynamic Programming(DP), and Binary Integration(BI), named RFT-DP-BI. A Markov model with unified range-velocity quantification is formulated to describe the maneuvering target’s motion. Based on this model, long-time hybrid integration is performed. Firstly, the whole integration time is divided into multiple time segments and coherent integration is performed in each segment via RFT. Secondly, non-coherent integration is performed in all segments via DP. Thirdly, 2/4 binary integration is performed to further improve the detection performance. Finally, the detection results are exported together with target range and velocity trajectories. The proposed method can perform the long-time integration of highly maneuvering targets with arbitrary forms of motion.Additionally, it has a low computational cost that is linear to the integration time. Both simulated and real radar data demonstrate that it offers good detection and estimation performances.展开更多
Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume.Continuous coverage from close-in"pop-up"targets in clutter to long-range t...Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume.Continuous coverage from close-in"pop-up"targets in clutter to long-range targets impacts selection of waveform parameters.The coherent processing interval(CPI)must be long enough to achieve a certain signal-to-noise ratio(SNR)that ensures the efficiency of detection.The condition of detection in the case of low SNR is analyzed,and three different cases that would occur during integration are discussed and a method to determine the CPI is presented.The simulation results show that targets detection with SNR as low as-26 dB in the experimental system can possibly determine the CPI.展开更多
An approach is proposed to realize a digital channelized receiver in the fractional Fourier domain （FRFD） for signal intercept applications. The presented architecture can be considered as a generalization of that i...An approach is proposed to realize a digital channelized receiver in the fractional Fourier domain （FRFD） for signal intercept applications. The presented architecture can be considered as a generalization of that in the traditional Fourier domain. Since the linear frequency modulation （LFM） signal has a good energy concentration in the FRFD, by choosing an appropriate fractional Fourier transform （FRFT） order, the presented architecture can concentrate the broadband LFM signal into only one sub-channel and that will prevent it from crossing several sub-channels. Thus the performance of the signal detection and parameter estimation after the sub-channel output will be improved significantly. The computational complexity is reduced enormously due to the implementation of the polyphase filter bank decomposition, thus the proposed architecture can be realized as efficiently as in the Fourier domain. The related simulation results are presented to verify the validity of the theories and methods involved in this paper.展开更多
Nanoparticles(NPs)are widely used for their special physical properties and released into the natural environment.When two types of NPs exist in the same environment,the presence of one type of NP may affect the prope...Nanoparticles(NPs)are widely used for their special physical properties and released into the natural environment.When two types of NPs exist in the same environment,the presence of one type of NP may affect the properties of the other type of NP.This study investigated the toxic effects of multi-walled carbon nanotubes(MWCNTs)and copper oxide nanoparticles(Cu O NPs)on Tetradesmus obliquus.Both NPs had toxic effects on algae,and the toxic effects of MWCNTs were significantly stronger than Cu O NPs which the 96-hr median effective concentration to algae were 33.8 and 169.2 mg/L,respectively.Oxidative stress and cell membrane damage were the main reasons for the toxicity of NPs to algae,and they were concentration-dependent,and the existence of Cu O NPs in some groups reduced cell membrane damage caused by MWCNTs which may because that Cu O NPs formed heteroaggregation with MWCNTs,reducing the contact of nanoparticles with cell membranes,then reducing physical damage.Scanning electron microscopy(SEM)and transmission electron microscope(TEM)results indicated cell damage,the heteroaggregation of MWCNTs-Cu O NPs and obvious nanoparticles internalization.In some groups,the presence of Cu O NPs significantly reduced reactive oxygen species(ROS)level induced by MWCNTs.However,for the highest concentration group,the ROS level was much higher than that of the two NPs alone treatment groups,which might be related to the high concentration of MWCNTs promoting the internalization of Cu O NPs.MWCNTs and Cu O NPs affected and interacted with each other,causing more complex toxic effects on aquatic organisms.展开更多
At present, most of the passive radar system researches utilize FM radios, TV broadcasts, navigation satellites,etc. as illuminators. The transmitted signals are not specifically designed radar waveforms. In this work...At present, most of the passive radar system researches utilize FM radios, TV broadcasts, navigation satellites,etc. as illuminators. The transmitted signals are not specifically designed radar waveforms. In this work, the frequency agile, phased array air surveillance radar(ASR) is used as the illuminator of opportunity to detect the weak target. The phased array technology can help realize beam agility to track targets from different aspects simultaneously. The frequency agility technology is widely employed in radar system design to increase the ability of anti-jamming and increase the detection probability. While the frequency bandwidth of radar signals is usually wide and the range resolution is high, the range cell migration effect is obvious during the long time integration of non-cooperative bistatic radar. In this context, coherent integration methods are not applicable. In this work, a parametric non-coherent integration algorithm based on task de-interweaving is proposed. Numerical experiments verify that this is effective in weak target detection.展开更多
基金supported by the National Natural Science Foundation of China(No.6157010118)。
文摘To detect highly maneuvering radar targets in low signal-to-noise ratio conditions, a hybrid long-time integration method is proposed, which combines Radon-Fourier Transform(RFT), Dynamic Programming(DP), and Binary Integration(BI), named RFT-DP-BI. A Markov model with unified range-velocity quantification is formulated to describe the maneuvering target’s motion. Based on this model, long-time hybrid integration is performed. Firstly, the whole integration time is divided into multiple time segments and coherent integration is performed in each segment via RFT. Secondly, non-coherent integration is performed in all segments via DP. Thirdly, 2/4 binary integration is performed to further improve the detection performance. Finally, the detection results are exported together with target range and velocity trajectories. The proposed method can perform the long-time integration of highly maneuvering targets with arbitrary forms of motion.Additionally, it has a low computational cost that is linear to the integration time. Both simulated and real radar data demonstrate that it offers good detection and estimation performances.
文摘Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume.Continuous coverage from close-in"pop-up"targets in clutter to long-range targets impacts selection of waveform parameters.The coherent processing interval(CPI)must be long enough to achieve a certain signal-to-noise ratio(SNR)that ensures the efficiency of detection.The condition of detection in the case of low SNR is analyzed,and three different cases that would occur during integration are discussed and a method to determine the CPI is presented.The simulation results show that targets detection with SNR as low as-26 dB in the experimental system can possibly determine the CPI.
基金supported by the Program for New Century Excellent Talents in University(NCET-06-0921)
文摘An approach is proposed to realize a digital channelized receiver in the fractional Fourier domain （FRFD） for signal intercept applications. The presented architecture can be considered as a generalization of that in the traditional Fourier domain. Since the linear frequency modulation （LFM） signal has a good energy concentration in the FRFD, by choosing an appropriate fractional Fourier transform （FRFT） order, the presented architecture can concentrate the broadband LFM signal into only one sub-channel and that will prevent it from crossing several sub-channels. Thus the performance of the signal detection and parameter estimation after the sub-channel output will be improved significantly. The computational complexity is reduced enormously due to the implementation of the polyphase filter bank decomposition, thus the proposed architecture can be realized as efficiently as in the Fourier domain. The related simulation results are presented to verify the validity of the theories and methods involved in this paper.
基金supported by the National Natural Science Foundation of China(Nos.51521006,51579095,51378190)Ecology and Environment Department of Hunan,the Program for Changjiang Scholars and Innovative Research Team in University(No.IRT-13R17)。
文摘Nanoparticles(NPs)are widely used for their special physical properties and released into the natural environment.When two types of NPs exist in the same environment,the presence of one type of NP may affect the properties of the other type of NP.This study investigated the toxic effects of multi-walled carbon nanotubes(MWCNTs)and copper oxide nanoparticles(Cu O NPs)on Tetradesmus obliquus.Both NPs had toxic effects on algae,and the toxic effects of MWCNTs were significantly stronger than Cu O NPs which the 96-hr median effective concentration to algae were 33.8 and 169.2 mg/L,respectively.Oxidative stress and cell membrane damage were the main reasons for the toxicity of NPs to algae,and they were concentration-dependent,and the existence of Cu O NPs in some groups reduced cell membrane damage caused by MWCNTs which may because that Cu O NPs formed heteroaggregation with MWCNTs,reducing the contact of nanoparticles with cell membranes,then reducing physical damage.Scanning electron microscopy(SEM)and transmission electron microscope(TEM)results indicated cell damage,the heteroaggregation of MWCNTs-Cu O NPs and obvious nanoparticles internalization.In some groups,the presence of Cu O NPs significantly reduced reactive oxygen species(ROS)level induced by MWCNTs.However,for the highest concentration group,the ROS level was much higher than that of the two NPs alone treatment groups,which might be related to the high concentration of MWCNTs promoting the internalization of Cu O NPs.MWCNTs and Cu O NPs affected and interacted with each other,causing more complex toxic effects on aquatic organisms.
基金supported by the National Natural Science Foundation of China(61401489)
文摘At present, most of the passive radar system researches utilize FM radios, TV broadcasts, navigation satellites,etc. as illuminators. The transmitted signals are not specifically designed radar waveforms. In this work, the frequency agile, phased array air surveillance radar(ASR) is used as the illuminator of opportunity to detect the weak target. The phased array technology can help realize beam agility to track targets from different aspects simultaneously. The frequency agility technology is widely employed in radar system design to increase the ability of anti-jamming and increase the detection probability. While the frequency bandwidth of radar signals is usually wide and the range resolution is high, the range cell migration effect is obvious during the long time integration of non-cooperative bistatic radar. In this context, coherent integration methods are not applicable. In this work, a parametric non-coherent integration algorithm based on task de-interweaving is proposed. Numerical experiments verify that this is effective in weak target detection.
