- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Synthetic Aperture Radar Target Feature Modulation Using Active Frequency Selective Surface
摘要： Target feature control on the synthetic aperture radar (SAR) image using the passive way is a challenging task in the field of SAR jamming. The conventional passive jamming devices such as corner reflectors and chaffs cannot achieve the flexible modulation of SAR target feature duo to their fixed scattering cross section. As a passive material, active frequency selective surface (AFSS) can dynamically control their electromagnetic characteristics and has been widely applied in the radar target stealth field. In this paper, a target feature modulation method based on AFSS is proposed against SAR. The method intermittently switches the scattering intensity of AFSS material and imposes periodic or random code amplitude modulation onto the radar signal. As a consequence, multi-false targets with verisimilar characteristics or cross-shaped areas are formed when modulated signal is received and processed by the victim SAR. Thus the protected target is difficult to detect and identify by SAR system. Microwave anechoic chamber experiments and measured SAR data simulations with different modulating parameters are separately conducted to demonstrate the effectiveness of the proposed method.
关键词： Synthetic aperture radar (SAR),reflectivity,target feature,periodic modulation,random code modulation,active frequency selective surface (AFSS)
更新于2025-09-04 15:30:14
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Imaging With 3-D Aperture Synthesis Radiometers
摘要： The spatial resolution is still a problem in passive microwave remote sensing, especially in low frequency. In recent years, the satellite formation flying has been proposed. Based on this technique, a large array is able to be synthesized in orbit to achieve higher spatial resolution. However, it is a big challenge for the control system to constrain all the satellites in a coplane in orbit. The 3-D array configuration is a good choice for a synthesized array based on satellite formation flying. In this paper, the complete formulation of visibility functions, including system imperfections, in a 3-D aperture synthesis radiometer (3-D ASR) is derived. The array factor of a 3-D ASR is defined. The reconstructed modified brightness temperature (BT) is a 3-D linear convolution of the modified BT and the array factor. Based on this relationship, the reconstruction method for a practical 3-D ASR is studied. The numerical results demonstrate that the reconstruction method is correct and stable. Finally, a discussion is given to analyze several existing methods that were proposed to reconstruct BT image for 3-D arrays in radio astronomy and earth observation. Compared with these existing methods, our imaging method is more suitable for earth observation based on the technique of satellites formation flying in low earth orbit. In addition, according to the derivations, some mature techniques that were developed for 2-D ASRs may be applied to 3-D ASRs.
关键词： visibility functions,image reconstruction,array factor,3-D aperture synthesis radiometers (3-D ASRs),modified brightness temperature (BT)
更新于2025-09-04 15:30:14
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - On the Use of SAR in Studies of Upwelling
摘要： In studies of upwelling, usually data from infrared and optical sensors are used which provide information on the sea surface temperature (SST) and the chlorophyll-a (Chl-a) concentration. In this paper we show that also synthetic aperture radars (SAR) images can give valuable contribution to such studies. Upwelling regions become detectable by SAR because they are associated with a reduction of the radar backscatter due to 1) a change of the stability of the air-sea interface or/and 2) the presence of biogenic slicks.
关键词： Agulhas current,upwelling,biogenic slicks,synthetic aperture radar
更新于2025-09-04 15:30:14
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Processing Spaceborne Interrupted FMCW SAR Data with Modified Aperture Interpolation Technique
摘要： Interrupted FMCW (IFMCW) SAR mode, which only employs a single antenna from a single micro-satellite, was proposed by Ahmed et al., recently. However, periodical data gaps will occur in the interrupted mode, caused by the process of switching the radar transmitter on and off. To solve this problem, in this paper, a modified aperture-interpolation-based approach is proposed to fill the data gaps. The approach can recover the gapped data with excellent performance and thus significantly suppress the artifacts (or ghosts) induced by the periodical data gaps. Processing results of real data acquired with an experimental airborne FMCW SAR system, demonstrate the effectiveness of the proposed approach.
关键词： artifacts,frequency-modulated continuous-wave (FMCW),Synthetic aperture radar (SAR)
更新于2025-09-04 15:30:14
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[IEEE 2018 China International SAR Symposium (CISS) - Shanghai, China (2018.10.10-2018.10.12)] 2018 China International SAR Symposium (CISS) - A Frequency Nonlinearity and Fluctuation Correction Method for Terahertz ISAR Imaging
摘要： Due to the high frequency band and wide bandwidth of Terahertz imaging radar, the high frequency generally performs unstable in system. In detail, the linearly frequency modulated (LFM) signal shows nonlinearity and the frequency center fluctuates randomly with time. It will potentially lead to the degradation of Terahertz inverse synthetic aperture radar (THz-ISAR) imaging quality. To address this problem, this paper presents a frequency nonlinearity and fluctuation correction method based on minimum entropy (ME). Following the error model, both the error can be corrected by applying the ME metric to the range and azimuth direction. The feasibility and adaptability of this proposal have been validated by simulation and real data experimental result.
关键词： minimum entropy,Terahertz,error correction,inverse synthetic aperture radar
更新于2025-09-04 15:30:14
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[IEEE 2018 21st International Conference on Information Fusion (FUSION 2018) - Cambridge (2018.7.10-2018.7.13)] 2018 21st International Conference on Information Fusion (FUSION) - Geometric Multi-Wavelet Total Variation for SAR Image Time Series Analysis
摘要： A time series issued from modern synthetic aperture radar satellite imaging sensors is a huge dataset composed by many hundreds of million pixels when observing large-scale earth structures such as big forests or glaciers. A concise monitoring of these large scale structures for anomaly spotting thus requires loading and analyzing huge spatio/polarimetric multi-temporal image series. The contributions of the present paper for the sake of parsimonious analysis of such huge datasets are associated with a framework having two main processing stages. The first stage is the derivation of an index called geometric multi-wavelet total variation for fast and robust anomaly spotting. This index is useful for identifying significant abnormal patterns appearing as geo-spatial non-stationarities in multi-wavelet total variation map. The second stage consists in the proposal of a concise asymmetric multi-date change information matrix on regions associated with significant multi-wavelet total variations. This stage is necessary for a fine characterization of change impacts on existing geo-spatial structures. Experimental tests based on Sentinel-1 data show relevant results on a wide Amazonian forest surrounding the Franco-Brazilian Oyapock Bridge.
关键词： Multi-Wavelets,Information fusion,Image Time Series,Geometric differencing,Multivariate Synthetic Aperture Radar
更新于2025-09-04 15:30:14
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FOCUSING TRANSLATIONAL VARIANT BISTATIC FORWARD-LOOKING SAR DATA BASED ON TWO-DIMENSIONAL NON-UNIFORM FFT
摘要： Forward-looking imaging has extensive potential applications, such as self-navigation and self-landing. By choosing proper geometry, bistatic synthetic aperture radar (BiSAR) can break through the limitations of monostatic SAR on forward-looking imaging and provide possibility of the forward-looking imaging. In this special bistatic configuration, two problems involving large range cell migration (RCM) and large range-azimuth coupling are introduced by the forward-looking beam, which make it difficult to use traditional data focusing algorithms. To address these problems, a novel Omega-K algorithm based on two-dimensional non-uniform FFT (2-D NUFFT) for translational variant (TV) bistatic forward-looking SAR (BFSAR) imaging is proposed in this paper. In this study, we derive an accurate spectrum expression based on two-dimensional principle of stationary phase (2-D POSP). 2-D NUFFT is utilized to eliminate the range-variant term, which can make full use of the data and improve the computational efficiency as well. The experimental results, presented herein, demonstrate the effectiveness and advantages of the proposed algorithm.
关键词： range-azimuth coupling,Omega-K algorithm,bistatic synthetic aperture radar,forward-looking imaging,2-D NUFFT,range cell migration
更新于2025-09-04 15:30:14
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HIGH-RESOLUTION GRID-INDEPENDENT IMAGING FOR TERAHERTZ 2-D SYNTHETIC APERTURE RADAR WITH SPATIAL UNDER-SAMPLING
摘要： For the purpose of two-dimensional (2-D) imaging in the Terahertz (THz) near field through 2-D synthetic aperture radar technology, Fourier transform (FT) is one of the most popular imaging ways. However, FT-based algorithms would encounter performance loss either when spatial sampling is under Nyquist frequency or there are off-grid scatterers in the scene of interest. Therefore, by exploiting the theory of matrix enhancement and continuous parameter estimation, we propose to use matrix enhancement and matrix pencil (MEMP) method and matched filter to deal with arbitrarily located scatterers when spatial under-sampling is adopted. Through constructing a specifically expanded matrix, the information of the scatterers involved in the small data set can be enhanced. Then, high-resolution grid-independence 2-D imaging can be achieved by the combination of MP and matched filter. Simulation results verify the effectiveness of the proposed algorithm.
关键词： Terahertz,matrix pencil,matrix enhancement,synthetic aperture radar,Fourier transform,grid-independent imaging,under-sampling
更新于2025-09-04 15:30:14
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Nonlinear absorption and Optical limiting of Ag–CdSe nano-hybrids of different growth times
摘要： Metal-semiconductor Nano-composites have enormous applications due to Plasmon –exciton coupling. Open aperture Z-scan is investigated for Ag–CdSe hybrid nanostructure, a toggle from saturable absorption process SA to reverse saturable absorption RSA is observed upon laser power increment. Proofs of crystal and morphological structure are given by selected area electron diffraction (SAED) and high resolution transmission electron microscope (HRTEM). Red shifting in photoluminescence spectra PL is observed which is ascribed to the particle size increment. Intriguing nonlinear findings can be used to engineer optical switching devices and optical limiters.
关键词： Photoluminescence,Open aperture Z scan,Ag:CdSe,Metal semiconductor nanohyrid structure,Optical limiting,Nonlinear absorption coefficient
更新于2025-09-04 15:30:14
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Method for Mueller matrix acquisition based on a division-of-aperture simultaneous polarimetric imaging technique
摘要： The Mueller matrix is an important parameter in the field of polarization optics, and how to measure it efficiently and accurately becomes considerably significant for its practical applications. In this paper, for the first time to our knowledge, we propose a new method for Mueller matrix acquisition based on a division-of-aperture simultaneous polarimetric imaging technique. Different from the traditional method where, for obtaining the 16 elements of the Mueller matrix, a 16-times-measurement must be conducted by jointly changing the states of polarization (SOPs) of the input and output lights, while in our method it is enough by just changing the SOPs of the input light 4 times. This time-saving and easy-calculating feature is owing to our specific polarimetric camera, where a full-Stokes vector is obtained easily since 3 linear SOPs (0o, 45o, 90o) and 1 circular SOP can be recorded simultaneously by spatially sharing the same detector. To simply verify the effectiveness of our method, a specific polarization device patched by 8 sub-polarizers is chosen as the sample to be measured. Experimental results show that they are consistent with the theoretical results, both in the Mueller matrix and the corresponding images. We predict that this method for Mueller matrix acquisition can get wide potential applications for rapid identifications in biomedicine and material science.
关键词： Division-of-aperture polarimetric camera,Mueller matrix,Liquid crystal variable retarder,Polarization
更新于2025-09-04 15:30:14