The Experts below are selected from a list of 7095 Experts worldwide ranked by ideXlab platform

Alberto Moreira - One of the best experts on this subject based on the ideXlab platform.

  • tandem l a technical perspective on future spaceborne sar sensors for earth observation
    IEEE Transactions on Geoscience and Remote Sensing, 2018
    Co-Authors: Sigurd Huber, Gerhard Krieger, Marwan Younis, Felipe Queiroz De Almeida, Michelangelo Villano, Alberto Moreira
    Abstract:

    Tandem-L is proposed as a spaceborne synthetic aperture radar (SAR) mission developed and operated by the German Aerospace Center in cooperation with several Helmholtz research centers and the German space industries. The mission concept comprises two fully polarimetric radar satellites providing monostatic and bistatic SAR imagery. A key feature of these SAR sensors is the employment of large lightweight unfurlable mesh reflectors fed by digital feed arrays. The main advantage of this new SAR system concept is the provision of large antenna apertures in space and flexible operation via reconfigurable feed electronics. By this, it becomes possible to map, for the first time, a continuous 350-km wide swath with a 7-m Azimuth Resolution with excellent noise equivalent sigma zero and ambiguity suppression. This paper shall give an overview on the technical aspects of the Tandem-L SAR instrument and antenna design. In particular, after a short review of the SAR system requirements, the concept of reflector SAR systems is outlined and the operation principle is presented. General guidelines for the design of array-fed reflector antennas with application to SAR imaging are given. Then, the optimization approach of the feed array design is detailed with a specific emphasis on a fixed beamforming concept in Azimuth. In this context, also the problem of cross-pol pattern mitigation is addressed. These optimization steps are shown to be crucial for achieving the performance requirements in quad-pol acquisitions. Beamforming in elevation is performed onboard the spacecraft via digital hardware. This paper presents the beamforming architecture on receive for Tandem-L, which would apply in general for instance also to planar multielevation beam SAR antennas with Scan-On-Receive capabilities. Tandem-L is operated as a staggered SAR, which means varying the pulse repetition interval from pulse to pulse. In this context, the major design challenges are presented. Moreover, the impact of pulse staggering on the imaging performance is discussed. Tandem-L’s SAR performance is presented by means of numerical simulations showing that the performance requirements imposed by the scientific user community could be met. The final part of this paper addresses options for high Azimuth Resolution imaging as well as a beamforming method for enhanced range ambiguity suppression.

  • Multichannel Staggered SAR Azimuth Processing
    IEEE Transactions on Geoscience and Remote Sensing, 2018
    Co-Authors: Felipe Queiroz De Almeida, Gerhard Krieger, Marwan Younis, Alberto Moreira
    Abstract:

    State-of-the-art and future spaceborne synthetic aperture radar (SAR) systems increasingly often face the requirement of providing high-Resolution images with reduced revisit times, requiring coverage of wide swaths. Since these are contradicting drivers in terms of system design, different alternatives for high-Resolution wide-swath SAR imaging have been investigated, relying on digital beamforming and the use of multiple receiver channels, both in elevation and Azimuth dimensions. In this context, staggered SAR, which operates with a pulse repetition frequency (PRF) variation, using a single channel in Azimuth proves itself as a promising alternative for covering wide continuous swaths with moderate Azimuth Resolution, whereas the use of multiple Azimuth receiver channels bears the potential of improving the Azimuth Resolution over a given swath, but has yet only been applied to systems with a fixed PRF. This paper introduces and analyzes in detail processing techniques suitable for the combination of these techniques, leading to novel multichannel staggered SAR imaging modes with the potential for very fine Azimuth Resolution over ultra-wide swaths. A system concept with 2-m Azimuth Resolution over a 400-km swath in quad-pol is provided as an example.

  • staggered sar high Resolution wide swath imaging by continuous pri variation
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Michelangelo Villano, Gerhard Krieger, Alberto Moreira
    Abstract:

    Synthetic aperture radar (SAR) is a remote sensing technique, capable of providing high-Resolution images independent of weather conditions and sunlight illumination. This makes SAR very attractive for the systematic observation of dynamic processes on the Earth's surface. However, conventional SAR systems are limited in that a wide swath can only be achieved at the expense of a degraded Azimuth Resolution. This limitation can be overcome by using systems with multiple receive apertures, displaced in along track, but a very long antenna is required to map a wide swath. If a relatively short antenna with a single aperture in along track is available, it is still possible to map a wide area: Multiple swaths can be, in fact, simultaneously imaged using digital beamforming in elevation, but “blind ranges” are present between adjacent swaths. This paper considers an innovative concept, staggered SAR, where the pulse repetition interval (PRI) is continuously varied. This concept allows the imaging of a wide continuous swath without the need for a long antenna with multiple apertures. The choice of the sequence of PRIs and the preprocessing of the raw data are discussed in detail, showing how the staggered SAR is even less affected by ambiguities of pointlike or extended targets with respect to a system with constant PRI, which simultaneously maps multiple swaths. Some system design examples are finally presented and compared.

  • advanced digital beamforming concepts for future sar systems
    International Geoscience and Remote Sensing Symposium, 2010
    Co-Authors: Gerhard Krieger, Marwan Younis, Nicolas Gebert, Sigurd Huber, Federica Bordoni, Anton Patyuchenko, Alberto Moreira
    Abstract:

    This paper reviews advanced multi-channel SAR system concepts for the imaging of wide swaths with high Resolution. Several novel system architectures employing both direct radiating arrays and reflector antennas fed by a digital array are introduced and compared to each other with regard to their imaging performance. In addition, innovative SAR imaging modes are proposed which enable the mapping of ultra-wide swaths with high Azimuth Resolution. The new techniques and technologies have the potential to enhance the imaging performance of future SAR systems by one order of magnitude if compared to state of the art SAR sensors like TerraSAR-X, ALOS, Radarsat-2 or Sentinel-1.

  • multichannel Azimuth processing in scansar and tops mode operation
    IEEE Transactions on Geoscience and Remote Sensing, 2010
    Co-Authors: Nicolas Gebert, Gerhard Krieger, Alberto Moreira
    Abstract:

    Due to a system-inherent limitation, conventional synthetic aperture radar (SAR) is incapable of imaging a wide swath with high geometric Resolution. This restriction can be overcome by systems with multiple receive channels in combination with an additional digital signal processing network. So far, the application of such digital beamforming algorithms for high-Resolution wide-swath SAR imaging has been restricted to multichannel systems in stripmap operation. However, in stripmap mode, the overall Azimuth antenna length restricts the achievable swath width, thus preventing very wide swaths as requested by future SAR missions. Consequently, new concepts for ultrawide-swath imaging are needed. A promising candidate is a SAR system with multiple Azimuth channels being operated in burst mode. This paper analyzes innovative ScanSAR and Terrain Observation by Progressive Scans (TOPS) system concepts with regard to multichannel Azimuth processing. For this, the theoretical analyses, performance figures, and SAR signal processing, which had previously been derived for multichannel stripmap mode, are extended to systems operating in burst modes. The investigations reveal that multichannel ScanSAR systems enable the imaging of ultrawide swaths with high Azimuth Resolution and compact antenna lengths. These considerations are embedded in a multichannel ScanSAR system design example to demonstrate its capability to image an ultrawide swath of 400 km with a high geometric Resolution of 5 m. In a next step, this system is adapted to TOPS mode operation, including an innovative “staircase” multichannel processing approach optimized for TOPS.

Gerhard Krieger - One of the best experts on this subject based on the ideXlab platform.

  • Instrument Error Model for Internal Calibration
    2020 German Microwave Conference (GeMiC), 2020
    Co-Authors: Jan Paul Kroll, Marwan Younis, Gerhard Krieger
    Abstract:

    Two key requirements for a modern space-borne Synthetic Aperture Radar (SAR) are a high Azimuth Resolution and a wide swath. This can be achieved by using SAR instruments with multiple digital channels. Differences between the channels lead to a reduced performance due to the degraded antenna pattern. To account for that the system has to be calibrated. In this paper we focus on the internal instrument calibration. The internal calibration concept suggested here allows for a simultaneous calibration during SAR transmit and receive operation. For the receive calibration, a single tone calibration signal, the CalTone, is sequentially coupled to the echo signal path. The transmit calibration is done by first characterizing the receiver (Radio Frequency Unit (RFU) and Digital Beam-forming Unit (DBU)) with a CalTone and then couple a part of the transmitted signal to the receiver. We created a mathematical model and a simulation tool to estimate the errors in such a calibration system and aid in the system design. The frequency of the signal can be varied to account for frequency dependencies. We show results with a calibration signals outside the SAR echo signal spectrum and with a varying frequency over time. We then introduce an improved method to estimate the drift and make a prediction. Further, the simulation tool allows for an analysis of the estimation errors.

  • tandem l a technical perspective on future spaceborne sar sensors for earth observation
    IEEE Transactions on Geoscience and Remote Sensing, 2018
    Co-Authors: Sigurd Huber, Gerhard Krieger, Marwan Younis, Felipe Queiroz De Almeida, Michelangelo Villano, Alberto Moreira
    Abstract:

    Tandem-L is proposed as a spaceborne synthetic aperture radar (SAR) mission developed and operated by the German Aerospace Center in cooperation with several Helmholtz research centers and the German space industries. The mission concept comprises two fully polarimetric radar satellites providing monostatic and bistatic SAR imagery. A key feature of these SAR sensors is the employment of large lightweight unfurlable mesh reflectors fed by digital feed arrays. The main advantage of this new SAR system concept is the provision of large antenna apertures in space and flexible operation via reconfigurable feed electronics. By this, it becomes possible to map, for the first time, a continuous 350-km wide swath with a 7-m Azimuth Resolution with excellent noise equivalent sigma zero and ambiguity suppression. This paper shall give an overview on the technical aspects of the Tandem-L SAR instrument and antenna design. In particular, after a short review of the SAR system requirements, the concept of reflector SAR systems is outlined and the operation principle is presented. General guidelines for the design of array-fed reflector antennas with application to SAR imaging are given. Then, the optimization approach of the feed array design is detailed with a specific emphasis on a fixed beamforming concept in Azimuth. In this context, also the problem of cross-pol pattern mitigation is addressed. These optimization steps are shown to be crucial for achieving the performance requirements in quad-pol acquisitions. Beamforming in elevation is performed onboard the spacecraft via digital hardware. This paper presents the beamforming architecture on receive for Tandem-L, which would apply in general for instance also to planar multielevation beam SAR antennas with Scan-On-Receive capabilities. Tandem-L is operated as a staggered SAR, which means varying the pulse repetition interval from pulse to pulse. In this context, the major design challenges are presented. Moreover, the impact of pulse staggering on the imaging performance is discussed. Tandem-L’s SAR performance is presented by means of numerical simulations showing that the performance requirements imposed by the scientific user community could be met. The final part of this paper addresses options for high Azimuth Resolution imaging as well as a beamforming method for enhanced range ambiguity suppression.

  • Multichannel Staggered SAR Azimuth Processing
    IEEE Transactions on Geoscience and Remote Sensing, 2018
    Co-Authors: Felipe Queiroz De Almeida, Gerhard Krieger, Marwan Younis, Alberto Moreira
    Abstract:

    State-of-the-art and future spaceborne synthetic aperture radar (SAR) systems increasingly often face the requirement of providing high-Resolution images with reduced revisit times, requiring coverage of wide swaths. Since these are contradicting drivers in terms of system design, different alternatives for high-Resolution wide-swath SAR imaging have been investigated, relying on digital beamforming and the use of multiple receiver channels, both in elevation and Azimuth dimensions. In this context, staggered SAR, which operates with a pulse repetition frequency (PRF) variation, using a single channel in Azimuth proves itself as a promising alternative for covering wide continuous swaths with moderate Azimuth Resolution, whereas the use of multiple Azimuth receiver channels bears the potential of improving the Azimuth Resolution over a given swath, but has yet only been applied to systems with a fixed PRF. This paper introduces and analyzes in detail processing techniques suitable for the combination of these techniques, leading to novel multichannel staggered SAR imaging modes with the potential for very fine Azimuth Resolution over ultra-wide swaths. A system concept with 2-m Azimuth Resolution over a 400-km swath in quad-pol is provided as an example.

  • staggered sar high Resolution wide swath imaging by continuous pri variation
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Michelangelo Villano, Gerhard Krieger, Alberto Moreira
    Abstract:

    Synthetic aperture radar (SAR) is a remote sensing technique, capable of providing high-Resolution images independent of weather conditions and sunlight illumination. This makes SAR very attractive for the systematic observation of dynamic processes on the Earth's surface. However, conventional SAR systems are limited in that a wide swath can only be achieved at the expense of a degraded Azimuth Resolution. This limitation can be overcome by using systems with multiple receive apertures, displaced in along track, but a very long antenna is required to map a wide swath. If a relatively short antenna with a single aperture in along track is available, it is still possible to map a wide area: Multiple swaths can be, in fact, simultaneously imaged using digital beamforming in elevation, but “blind ranges” are present between adjacent swaths. This paper considers an innovative concept, staggered SAR, where the pulse repetition interval (PRI) is continuously varied. This concept allows the imaging of a wide continuous swath without the need for a long antenna with multiple apertures. The choice of the sequence of PRIs and the preprocessing of the raw data are discussed in detail, showing how the staggered SAR is even less affected by ambiguities of pointlike or extended targets with respect to a system with constant PRI, which simultaneously maps multiple swaths. Some system design examples are finally presented and compared.

  • advanced digital beamforming concepts for future sar systems
    International Geoscience and Remote Sensing Symposium, 2010
    Co-Authors: Gerhard Krieger, Marwan Younis, Nicolas Gebert, Sigurd Huber, Federica Bordoni, Anton Patyuchenko, Alberto Moreira
    Abstract:

    This paper reviews advanced multi-channel SAR system concepts for the imaging of wide swaths with high Resolution. Several novel system architectures employing both direct radiating arrays and reflector antennas fed by a digital array are introduced and compared to each other with regard to their imaging performance. In addition, innovative SAR imaging modes are proposed which enable the mapping of ultra-wide swaths with high Azimuth Resolution. The new techniques and technologies have the potential to enhance the imaging performance of future SAR systems by one order of magnitude if compared to state of the art SAR sensors like TerraSAR-X, ALOS, Radarsat-2 or Sentinel-1.

Jianyu Yang - One of the best experts on this subject based on the ideXlab platform.

  • A Sparse Denoising-Based Super-Resolution Method for Scanning Radar Imaging
    'MDPI AG', 2021
    Co-Authors: Qiping Zhang, Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang
    Abstract:

    Scanning radar enables wide-range imaging through antenna scanning and is widely used for radar warning. The Rayleigh criterion indicates that narrow beams of radar are required to improve the Azimuth Resolution. However, a narrower beam means a larger antenna aperture. In practical applications, due to platform limitations, the antenna aperture is limited, resulting in a low Azimuth Resolution. The conventional sparse super-Resolution method (SSM) has been proposed for improving the Azimuth Resolution of scanning radar imaging and achieving superior performance. This method uses the L1 norm to represent the sparse prior of the target and solves the L1 regularization problem to achieve super-Resolution imaging under the regularization framework. The Resolution of strong-point targets is improved efficiently. However, for some targets with typical shapes, the strong sparsity of the L1 norm treats them as strong-point targets, resulting in the loss of shape characteristics. Thus, we can only see the strong points in its processing results. However, in some applications that need to identify targets in detail, SSM can lead to false judgments. In this paper, a sparse denoising-based super-Resolution method (SDBSM) is proposed to compensate for the deficiency of traditional SSM. The proposed SDBSM uses a sparse minimization scheme for denoising, which helps to reduce the influence of noise. Then, the super-Resolution imaging is achieved by alternating iterative denoising and deconvolution. As the proposed SDBSM uses the L1 norm for denoising rather than deconvolution, the strong sparsity constraint of the L1 norm is reduced. Therefore, it can effectively preserve the shape of the target while improving the Azimuth Resolution. The performance of the proposed SDBSM was demonstrated via simulation and real data processing results

  • super Resolution surface mapping for scanning radar inverse filtering based on the fast iterative adaptive approach
    IEEE Transactions on Geoscience and Remote Sensing, 2018
    Co-Authors: Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang
    Abstract:

    High-Resolution scanning radar mapping of the surface is an effective tool for addressing concerns in local environmental and social investigation fields. Regrettably, the Azimuth Resolution of a scanning radar is constrained by the antenna beamwidth. Multiple super-Resolution approaches have been applied to the scanning radar to enhance the Azimuth Resolution, but they suffer from limited Resolution improvement. In this paper, a methodology to derive surface estimates from the scanning radar at an improved Azimuth Resolution is proposed. We first consider the truncated spectrum by discarding the unreliable frequencies to suppress the noise amplification. Then, based on the iterative adaptive approach (IAA), a novel inverse filtering method is formulated to obtain lower sidelobes and a higher Resolution. Finally, by taking advantage of the Fourier property of the steering matrix and the Toeplitz structure of the covariance matrix, we exploit the Gohberg-Semencul representation and the data-dependent trigonometric polynomials to derive a fast IAA (FIAA)-based inverse filtering to mitigate the computational burden. Simulation results and real data processing demonstrate that the proposed FIAA-based inverse filtering outperforms the existing super-Resolution approaches in Resolution improvement and results in a higher computational efficiency.

  • doppler beam sharpening imaging based on fast iterative adaptive approach
    IEEE Radar Conference, 2017
    Co-Authors: Haiguang Yang, Yongchao Zhang, Yin Zhang, Yulin Huang, Deqing Mao, Jianyu Yang
    Abstract:

    This paper proposes a Doppler beam sharpening (DBS) imaging method to achieve the high Azimuth Resolution in the forward-squint region based on fast iterative adaptive approach (F-IAA). In conventional DBS imaging, fast Fourier transform (FFT) method is adopted to obtain the estimation of Doppler center frequencies of targets, but it suffers from the low Resolution and high sidelobes. Though a weighted least-squares based, nonparametric iterative adaptive approach (IAA) is proposed to instead of FFT method, it can not be applied to engineering applications because of its large computational complexity. In this paper, a F-IAA method, using the Gohberg-Semencul (GS)-type factorization of IAA covariance matrix, is introduced to reduce the computational complexity of brute force IAA method. Compared with the brute force IAA method, the F-IAA method mainly reduces the computational complexity of the operation of IAA covariance matrix and the inverse operation of covariance matrix. The effect is testified in simulation.

  • TSVD with least squares optimization for scanning radar angular super-Resolution
    2017 IEEE Radar Conference (RadarConf), 2017
    Co-Authors: Wu Yang, Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang
    Abstract:

    The poor Azimuth Resolution limits the application of the scanning radar. Several super-Resolution methods have been proposed to improve the angular Resolution. However, they suffer from noise amplification and edge loss. In this paper, a novel angular super-Resolution approach for scanning radar is presented. Firstly, the angular super-Resolution problem is converted into an inverse problem, which is described by a linear combination of a set of singular values. Through singular value decomposition (SVD) method, it is demonstrated that the small singular values cause the solution to be unreliable. Then to suppress noise amplification and resolve the issue that the edge information is lost when the convolution matrix is truncated to be square, the truncated SVD (TSVD) with the least squares optimization technique, termed as LSTSVD is developed. Simulations and experimental results demonstrate that the proposed LSTSVD method can improve the Azimuth Resolution without noise amplification and loss of edge information.

  • Angular SuperResolution for Scanning Radar With Improved Regularized Iterative Adaptive Approach
    IEEE Geoscience and Remote Sensing Letters, 2016
    Co-Authors: Yongchao Zhang, Yin Zhang, Yulin Huang, Wenchao Li, Jianyu Yang
    Abstract:

    In this letter, an improved regularized iterative adaptive approach (IAA) is proposed for scanning radar angular superResolution. Because the IAA requires matrix inversion, the increasing condition number of the covariance matrix leads to the ill-posed problem of the IAA. Based on this reality, the diagonal loading method is introduced to solve the ill-posed problem. Because the loading value controls the tradeoff between the Azimuth Resolution and noise amplification, we use the radiometer uncertainty principle to determine the optimum loading value. When compared with the existing angular superResolution approaches, the proposed regularized IAA is shown to provide significant Resolution improvement. Numerical results illustrate the superior performance of the proposed regularized IAA.

Nicolas Gebert - One of the best experts on this subject based on the ideXlab platform.

  • advanced digital beamforming concepts for future sar systems
    International Geoscience and Remote Sensing Symposium, 2010
    Co-Authors: Gerhard Krieger, Marwan Younis, Nicolas Gebert, Sigurd Huber, Federica Bordoni, Anton Patyuchenko, Alberto Moreira
    Abstract:

    This paper reviews advanced multi-channel SAR system concepts for the imaging of wide swaths with high Resolution. Several novel system architectures employing both direct radiating arrays and reflector antennas fed by a digital array are introduced and compared to each other with regard to their imaging performance. In addition, innovative SAR imaging modes are proposed which enable the mapping of ultra-wide swaths with high Azimuth Resolution. The new techniques and technologies have the potential to enhance the imaging performance of future SAR systems by one order of magnitude if compared to state of the art SAR sensors like TerraSAR-X, ALOS, Radarsat-2 or Sentinel-1.

  • multichannel Azimuth processing in scansar and tops mode operation
    IEEE Transactions on Geoscience and Remote Sensing, 2010
    Co-Authors: Nicolas Gebert, Gerhard Krieger, Alberto Moreira
    Abstract:

    Due to a system-inherent limitation, conventional synthetic aperture radar (SAR) is incapable of imaging a wide swath with high geometric Resolution. This restriction can be overcome by systems with multiple receive channels in combination with an additional digital signal processing network. So far, the application of such digital beamforming algorithms for high-Resolution wide-swath SAR imaging has been restricted to multichannel systems in stripmap operation. However, in stripmap mode, the overall Azimuth antenna length restricts the achievable swath width, thus preventing very wide swaths as requested by future SAR missions. Consequently, new concepts for ultrawide-swath imaging are needed. A promising candidate is a SAR system with multiple Azimuth channels being operated in burst mode. This paper analyzes innovative ScanSAR and Terrain Observation by Progressive Scans (TOPS) system concepts with regard to multichannel Azimuth processing. For this, the theoretical analyses, performance figures, and SAR signal processing, which had previously been derived for multichannel stripmap mode, are extended to systems operating in burst modes. The investigations reveal that multichannel ScanSAR systems enable the imaging of ultrawide swaths with high Azimuth Resolution and compact antenna lengths. These considerations are embedded in a multichannel ScanSAR system design example to demonstrate its capability to image an ultrawide swath of 400 km with a high geometric Resolution of 5 m. In a next step, this system is adapted to TOPS mode operation, including an innovative “staircase” multichannel processing approach optimized for TOPS.

  • sar signal reconstruction from non uniform displaced phase centre sampling in the presence of perturbations
    International Geoscience and Remote Sensing Symposium, 2005
    Co-Authors: Nicolas Gebert, Gerhard Krieger, Alberto Moreira
    Abstract:

    The displaced phase centre (DPC) technique enables a wide swath SAR with high Azimuth Resolution. In classic DPC systems, the pulse repetition frequency (PRF), sensor velocity and antenna length underlie a stringent timing requirement and any deviation will result in a non-uniform sampling of the syn­thetic aperture. This restriction can be overcome by the use of a recon­struction algorithm, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling. This paper ex­plains limitations of the reconstruction imposed by the processing and the impacts on the ambiguity suppression. The potential of the algorithm when applied to DPC systems like TerraSAR-X with its split receive antenna is demon­strated and the benefits re­sulting from the additional receive ap­ertur e regarding swath width and Resolution are pointed out. Further on, the impact of ad­ditive and phase noise on the recon­struction and its sensitivity against these perturbations are shown.

  • sar signal reconstruction from non uniform displaced phase centre sampling
    International Geoscience and Remote Sensing Symposium, 2004
    Co-Authors: Gerhard Krieger, Nicolas Gebert, Alberto Moreira
    Abstract:

    The displaced phase centre (DPC) technique enables a wide swath SAR with high Azimuth Resolution. In a classic DPC system, the PRF has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF results in a non-uniform sampling of the synthetic aperture. This paper shows that an unambiguous reconstruction of the SAR signal is also possible in case of such a non-optimum PRF. For this, an innovative reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling of the synthetic aperture. This algorithm also has a great potential for multistatic satellite constellations as well as the dual receive antennas in Radarsat II and TerraSAR-X

  • unambiguous sar signal reconstruction from nonuniform displaced phase center sampling
    IEEE Geoscience and Remote Sensing Letters, 2004
    Co-Authors: Gerhard Krieger, Nicolas Gebert, Alberto Moreira
    Abstract:

    The displaced phase center (DPC) technique will enable a wide-swath synthetic aperture radar (SAR) with high Azimuth Resolution. In a classic DPC system, the pulse repetition frequency (PRF) has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF will result in a nonuniform sampling of the synthetic aperture. This letter derives an innovative reconstruction algorithm and shows that an unambiguous reconstruction of a SAR signal is possible for nonuniform sampling of the synthetic aperture. This algorithm will also have great potential for multistatic satellite constellations as well as the dual receive antenna mode in Radarsat 2 and TerraSAR-X.

Yongchao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • A Sparse Denoising-Based Super-Resolution Method for Scanning Radar Imaging
    'MDPI AG', 2021
    Co-Authors: Qiping Zhang, Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang
    Abstract:

    Scanning radar enables wide-range imaging through antenna scanning and is widely used for radar warning. The Rayleigh criterion indicates that narrow beams of radar are required to improve the Azimuth Resolution. However, a narrower beam means a larger antenna aperture. In practical applications, due to platform limitations, the antenna aperture is limited, resulting in a low Azimuth Resolution. The conventional sparse super-Resolution method (SSM) has been proposed for improving the Azimuth Resolution of scanning radar imaging and achieving superior performance. This method uses the L1 norm to represent the sparse prior of the target and solves the L1 regularization problem to achieve super-Resolution imaging under the regularization framework. The Resolution of strong-point targets is improved efficiently. However, for some targets with typical shapes, the strong sparsity of the L1 norm treats them as strong-point targets, resulting in the loss of shape characteristics. Thus, we can only see the strong points in its processing results. However, in some applications that need to identify targets in detail, SSM can lead to false judgments. In this paper, a sparse denoising-based super-Resolution method (SDBSM) is proposed to compensate for the deficiency of traditional SSM. The proposed SDBSM uses a sparse minimization scheme for denoising, which helps to reduce the influence of noise. Then, the super-Resolution imaging is achieved by alternating iterative denoising and deconvolution. As the proposed SDBSM uses the L1 norm for denoising rather than deconvolution, the strong sparsity constraint of the L1 norm is reduced. Therefore, it can effectively preserve the shape of the target while improving the Azimuth Resolution. The performance of the proposed SDBSM was demonstrated via simulation and real data processing results

  • super Resolution surface mapping for scanning radar inverse filtering based on the fast iterative adaptive approach
    IEEE Transactions on Geoscience and Remote Sensing, 2018
    Co-Authors: Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang
    Abstract:

    High-Resolution scanning radar mapping of the surface is an effective tool for addressing concerns in local environmental and social investigation fields. Regrettably, the Azimuth Resolution of a scanning radar is constrained by the antenna beamwidth. Multiple super-Resolution approaches have been applied to the scanning radar to enhance the Azimuth Resolution, but they suffer from limited Resolution improvement. In this paper, a methodology to derive surface estimates from the scanning radar at an improved Azimuth Resolution is proposed. We first consider the truncated spectrum by discarding the unreliable frequencies to suppress the noise amplification. Then, based on the iterative adaptive approach (IAA), a novel inverse filtering method is formulated to obtain lower sidelobes and a higher Resolution. Finally, by taking advantage of the Fourier property of the steering matrix and the Toeplitz structure of the covariance matrix, we exploit the Gohberg-Semencul representation and the data-dependent trigonometric polynomials to derive a fast IAA (FIAA)-based inverse filtering to mitigate the computational burden. Simulation results and real data processing demonstrate that the proposed FIAA-based inverse filtering outperforms the existing super-Resolution approaches in Resolution improvement and results in a higher computational efficiency.

  • doppler beam sharpening imaging based on fast iterative adaptive approach
    IEEE Radar Conference, 2017
    Co-Authors: Haiguang Yang, Yongchao Zhang, Yin Zhang, Yulin Huang, Deqing Mao, Jianyu Yang
    Abstract:

    This paper proposes a Doppler beam sharpening (DBS) imaging method to achieve the high Azimuth Resolution in the forward-squint region based on fast iterative adaptive approach (F-IAA). In conventional DBS imaging, fast Fourier transform (FFT) method is adopted to obtain the estimation of Doppler center frequencies of targets, but it suffers from the low Resolution and high sidelobes. Though a weighted least-squares based, nonparametric iterative adaptive approach (IAA) is proposed to instead of FFT method, it can not be applied to engineering applications because of its large computational complexity. In this paper, a F-IAA method, using the Gohberg-Semencul (GS)-type factorization of IAA covariance matrix, is introduced to reduce the computational complexity of brute force IAA method. Compared with the brute force IAA method, the F-IAA method mainly reduces the computational complexity of the operation of IAA covariance matrix and the inverse operation of covariance matrix. The effect is testified in simulation.

  • TSVD with least squares optimization for scanning radar angular super-Resolution
    2017 IEEE Radar Conference (RadarConf), 2017
    Co-Authors: Wu Yang, Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang
    Abstract:

    The poor Azimuth Resolution limits the application of the scanning radar. Several super-Resolution methods have been proposed to improve the angular Resolution. However, they suffer from noise amplification and edge loss. In this paper, a novel angular super-Resolution approach for scanning radar is presented. Firstly, the angular super-Resolution problem is converted into an inverse problem, which is described by a linear combination of a set of singular values. Through singular value decomposition (SVD) method, it is demonstrated that the small singular values cause the solution to be unreliable. Then to suppress noise amplification and resolve the issue that the edge information is lost when the convolution matrix is truncated to be square, the truncated SVD (TSVD) with the least squares optimization technique, termed as LSTSVD is developed. Simulations and experimental results demonstrate that the proposed LSTSVD method can improve the Azimuth Resolution without noise amplification and loss of edge information.

  • Angular SuperResolution for Scanning Radar With Improved Regularized Iterative Adaptive Approach
    IEEE Geoscience and Remote Sensing Letters, 2016
    Co-Authors: Yongchao Zhang, Yin Zhang, Yulin Huang, Wenchao Li, Jianyu Yang
    Abstract:

    In this letter, an improved regularized iterative adaptive approach (IAA) is proposed for scanning radar angular superResolution. Because the IAA requires matrix inversion, the increasing condition number of the covariance matrix leads to the ill-posed problem of the IAA. Based on this reality, the diagonal loading method is introduced to solve the ill-posed problem. Because the loading value controls the tradeoff between the Azimuth Resolution and noise amplification, we use the radiometer uncertainty principle to determine the optimum loading value. When compared with the existing angular superResolution approaches, the proposed regularized IAA is shown to provide significant Resolution improvement. Numerical results illustrate the superior performance of the proposed regularized IAA.