Azimuth Phase Center Adaptive Adjustment upon Reception for High-Resolution Wide-Swath Imaging

Xu, Wei; Hu, Jialuo; Huang, Pingping; Tan, Weixian; Dong, Yifan

doi:10.3390/s19194277

Cited by 5 publications

(9 citation statements)

References 21 publications

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“…In the azimuth multichannel GEO-SA-BiSAR system, the different range history of the moving target causes the different multichannel impulse response in (23) with azimuth time delay and phase shift. To analyze the effects of the target velocity on these parameters in detail, designed simulation experiments are implemented, and Table 1 lists the corresponding simulation parameters.…”

Section: Effects Of the Target Velocity On Imaging Resultsmentioning

confidence: 99%

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Azimuth Multichannel Reconstruction for Moving Targets in Geosynchronous Spaceborne–Airborne Bistatic SAR

Wei

Huang

et al. 2020

Remote Sensing

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In a multichannel geosynchronous spaceborne–airborne bistatic synthetic aperture radar (GEO-SA-BiSAR) system, the airborne receiver can obtain high-resolution microwave images with good signal-to-noise ratios (SNRs) by passively receiving echoes from the desired area. Since the Doppler modulation and range history of a moving target are obviously different from a stationary target, a signal geometry model for moving targets in multichannel GEO-SA-BiSAR is established in this paper. According to simulation results, the along track velocity introduces target defocusing in azimuth, and the slant range velocity mainly causes multiple false targets. To resolve these problems, a modified multichannel reconstruction method in azimuth channel GEO-SA-BiSAR is proposed according to the azimuth multichannel impulse response of the imaged moving target. Before azimuth multichannel raw data combination, both spatial-variant range cell migration correction (RCMC) and azimuth nonlinear chirp scaling (ANLCS) should be performed to reduce the influence of the range offset and lower the Doppler bandwidth of the whole raw data, respectively. Afterward, a novel azimuth multichannel reconstruction algorithm is carried out via the modified reconstruction matrix based on the estimated target velocity. The target slant range velocity estimation is implemented by introducing the signal intensity ratio (SIR). Compared with the conventional method for the stationary target to handle the raw data of the moving target, the false targets could be obviously suppressed by using the proposed approach. Imaging results on both simulated point and distributed scene targets validate the proposed multichannel reconstruction approach.

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Section: Effects Of the Target Velocity On Imaging Resultsmentioning

confidence: 99%

“…Compared with the stationary target in multichannel GEO-SA-BiSAR [22,23], the moving target has a different range history and Doppler modulation [24,25]. If azimuth multichannel reconstruction and imaging approaches for stationary scenes were adopted to handle the echoes of moving targets, imaging quality would be seriously reduced.…”

Section: Introductionmentioning

confidence: 99%

Azimuth Multichannel Reconstruction for Moving Targets in Geosynchronous Spaceborne–Airborne Bistatic SAR

Wei

Huang

et al. 2020

Remote Sensing

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“…Similar to the NLFM signal, the non-uniform frequency distribution should be obtained for sidelobe suppression without window weighting. The method to obtain the non-uniform frequency distribution via adjusting the frequency modulation rate cannot be implemented in azimuth, since the Doppler modulation rate is only related to the imaging geometry and cannot be easily changed [15,16]. The way to obtain the non-uniform Doppler frequency distribution is by using azimuth non-uniform sampling (ANUS) [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging

Zhang

Fang³

et al. 2021

Sensors

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In synthetic aperture radar (SAR) imaging, geometric resolution, sidelobe level (SLL) and signal-to-noise ratio (SNR) are the most important parameters for measuring the SAR image quality. The staring spotlight mode continuously transmits signals to a fixed area by steering the azimuth beam to acquire azimuth high geometric resolution, and its two-dimensional (2D) impulse response with the low SLL is usually obtained from the 2D weighted power spectral density (PSD) by the selected weighting window function. However, this results in the SNR reduction due to 2D amplitude window weighting. In this paper, the staring spotlight SAR with nonlinear frequency modulation (NLFM) signal and azimuth non-uniform sampling (ANUS) is proposed to obtain high geometric resolution SAR images with the low SLL and almost without any SNR reduction. The NLFM signal obtains non-equal interval frequency sampling points under uniform time sampling by adjusting the instantaneous chirp rate. Its corresponding PSD is similar to the weighting window function, and its pulse compression result without amplitude window weighting has low sidelobes. To obtain a similar Doppler frequency distribution for low sidelobe imaging in azimuth, the received SAR echoes are designed to be non-uniformly sampled in azimuth, in which the sampling sequence is dense in middle and sparse in both ends, and azimuth compression result with window weighting would also have low sidelobes. According to the echo model of the proposed imaging mode, both the back projection algorithm (BPA) and range migration algorithm (RMA) are modified and presented to handle the raw data of the proposed imaging mode. Both imaging results on simulated targets and experimental real SAR data processing results of a ground-based radar validate the proposed low sidelobe imaging mode.

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“…The results show that: (a) the image resulting from beamforming features better azimuth ambiguity-to-signal ratio and (b) the proposed approach for PRF selection allows one to individuate a subset of the available images leading to uniform distribution of samples which can be used to support FF-SAR processing.reducing the collision risk [18,19]. System timing is thus more intricate than for a multichannel SAR [20], and proper selection of the pulse repetition frequency (PRF) is mandatory. This work firstly contributes to that topic presenting an approach to PRF selection.A key feature of FF-SAR is the capability to synthesize an image with a higher PRF with respect to the actual PRF of the transmitter.…”

mentioning

confidence: 99%

“…reducing the collision risk [18,19]. System timing is thus more intricate than for a multichannel SAR [20], and proper selection of the pulse repetition frequency (PRF) is mandatory. This work firstly contributes to that topic presenting an approach to PRF selection.…”

mentioning

confidence: 99%

PRF Selection in Formation-Flying SAR: Experimental Verification on Sentinel-1 Monostatic Repeat-Pass Data

et al. 2019

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Formation-flying synthetic aperture radar (FF-SAR) enables new working modes and can achieve very high performance through a series of very compact, low-weight, satellite platforms thanks to passive operations of conveniently distributed formation-flying receivers. System timing is a crucial aspect of FF-SAR. The manuscript presents a novel approach to pulse repetition frequency (PRF) selection in order to obtain a uniform distribution of samples at given platform positions. A digital beamforming algorithm is applied on a stack of monostatic repeat-pass images collected by the Sentinel-1 system to test the validity of the PRF selection method. Processed images were thus properly selected to achieve the best merit index measuring the quality of samples distribution. The results show that: (a) the image resulting from beamforming features better azimuth ambiguity-to-signal ratio and (b) the proposed approach for PRF selection allows one to individuate a subset of the available images leading to uniform distribution of samples which can be used to support FF-SAR processing.

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Azimuth Phase Center Adaptive Adjustment upon Reception for High-Resolution Wide-Swath Imaging

Cited by 5 publications

References 21 publications

Azimuth Multichannel Reconstruction for Moving Targets in Geosynchronous Spaceborne–Airborne Bistatic SAR

Azimuth Multichannel Reconstruction for Moving Targets in Geosynchronous Spaceborne–Airborne Bistatic SAR

Staring Spotlight SAR with Nonlinear Frequency Modulation Signal and Azimuth Non-Uniform Sampling for Low Sidelobe Imaging

PRF Selection in Formation-Flying SAR: Experimental Verification on Sentinel-1 Monostatic Repeat-Pass Data

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