Phaseless Terahertz Coded-Aperture Imaging for Sparse Target Based on Phase Retrieval Algorithm

Phaseless terahertz coded-aperture imaging (PL-TCAI) is a novel radar computational imaging method that utilizes the coded aperture and the incoherent detector array to achieve forward-looking and high-resolution imaging without relying on relative motion. In this paper, we propose a more reasonable and compact architecture for the PL-TCAI system and derive the imaging model of PL-TCAI based on the random frequency-hopping signal. Since most phase retrieval algorithms for PL-TCAI utilize only the intensity of echo signals to accurately reconstruct the target, excessive measurement samples are usually required. In order to reduce the number of measurement samples required for imaging, this paper proposes a sparse Wirtinger flow algorithm with optimal stepsize (SWFOS) by using the sparse prior of the target. The specific procedures of the SWFOS algorithm include the support recovery, initialization by truncated spectral method, iteration via gradient descent scheme, hard threshold operation, and stepsize optimization of iteration. Numerical simulations are performed, and the results show that the SWFOS algorithm not only has good performance for the PR problem, but can also sharply reduce the number of measurement samples required for imaging in the PL-TCAI system.

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Phaseless Terahertz Coded-Aperture Imaging Based on Deep Generative Neural Network

Remote Sensing ◽

10.3390/rs13040671 ◽

2021 ◽

Vol 13 (4) ◽

pp. 671

Author(s):

Fengjiao Gan ◽

Ziyang Yuan ◽

Chenggao Luo ◽

Hongqiang Wang

Keyword(s):

Phase Retrieval ◽

Generative Models ◽

System Structure ◽

Retrieval Algorithm ◽

Coded Aperture ◽

Intensity Measurements ◽

Coded Aperture Imaging ◽

Extended Target ◽

The Matrix ◽

High Resolution Reconstruction

As a promising terahertz radar imaging technology, phaseless terahertz coded-aperture imaging (PL-TCAI) has many advantages such as simple system structure, forward-looking imaging and staring imaging and so forth. However, it is very difficult to recover a target only from its intensity measurements. Although some methods have been proposed to deal with this problem, they require a large number of intensity measurements for both sparse and extended target reconstruction. In this work, we propose a method for PL-TCAI by modeling target scattering coefficient as being in the range of a generative model. Theoretically, we analyze and model the system structure, derive the matrix imaging equation, and then study the deep phase retrieval algorithm. Numerical tests based on different generative models show that the targets with the different spareness can achieve high resolution reconstruction when the number of intensity measurements are smaller than the number of target grids. Also, we find that the proposed method has good anti-noise and stability.

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Three-Dimensional Terahertz Coded-Aperture Imaging Based on Back Projection

Sensors ◽

10.3390/s18082510 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2510 ◽

Cited By ~ 1

Author(s):

Shuo Chen ◽

Chenggao Luo ◽

Hongqiang Wang ◽

Wenpeng Wang ◽

Long Peng ◽

...

Keyword(s):

Computational Complexity ◽

Pulse Compression ◽

Signal To Noise Ratio ◽

Reference Signal ◽

Three Dimensional ◽

Coded Aperture ◽

Imaging Method ◽

Back Projection ◽

Coded Aperture Imaging ◽

Resolution Imaging

Terahertz coded-aperture imaging (TCAI) can overcome the difficulties of traditional radar in forward-looking and high-resolution imaging. Three-dimensional (3D) TCAI relies mainly on the reference-signal matrix (RSM), the large size and poor accuracy of which reduce the computational efficiency and imaging ability, respectively. According to the previous research on TCAI, traditional TCAI cannot reduce the heavy computational burden while the improved TCAI achieve reconstructing the target parts of different ranges in parallel. However, large-sized RSM still accounts for the computational complexity of traditional TCAI and the improved TCAI. Therefore, this paper proposes a more efficient imaging method named back projection (BP)-TCAI (BP-TCAI). Referring to the basic principle of BP, BP-TCAI can not only divide the scattering information in different ranges but also project the range profiles into different imaging subareas. In this way, the target parts in different subareas can be reconstructed simultaneously to synthesize the whole 3D target and thus decomposes the computational complexity thoroughly. During the pulse compression and projection processes, the signal-to-noise ratio (SNR) of BP-TCAI is also improved. This present the imaging method, model and procedures of traditional TCAI, the improved TCAI and the proposed BP-TCAI. Numerical experimental results prove BP-TCAI to be more effective and efficient than previous imaging methods of TCAI. Besides, BP-TCAI can also be seen as synthetic aperture radar (SAR) imaging with coding technology. Therefore, BP-TCAI opens a future gate combining traditional SAR and coded-aperture imaging.

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Phaseless Terahertz Coded-Aperture Imaging Based on Incoherent Detection

Sensors ◽

10.3390/s19020226 ◽

2019 ◽

Vol 19 (2) ◽

pp. 226 ◽

Cited By ~ 3

Author(s):

Long Peng ◽

Chenggao Luo ◽

Bin Deng ◽

Hongqiang Wang ◽

Yuliang Qin ◽

...

Keyword(s):

High Resolution ◽

High Speed ◽

Phase Retrieval ◽

Time Frame ◽

Frame Rate ◽

Future Research ◽

Coded Aperture ◽

Main Work ◽

Coded Aperture Imaging ◽

The Matrix

In this paper, we propose a phaseless terahertz coded-aperture imaging (PTCAI) method by using a single incoherent detector or an incoherent detection array. We at first analyze and model the system architecture, derive the matrix imaging equation, and then study the phase retrieval techniques to reconstruct the original target with high resolution. Numerical experiments are performed and the results show that the proposed method can significantly reduce the system complexity in the receiving process while maintaining high resolution imaging capability. Furthermore, the approach of using incoherent detection array instead of single detector is capable of decreasing the encoding and sampling times, and therefore helps to improve the imaging frame rate. In our future research, the method proposed in this paper will be experimentally tested and validated, and high-speed PTCAI at nearly real-time frame rates will be the main work.

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A three-dimensional imaging method based on the principle of coded aperture imaging

10.1117/12.612667 ◽

2005 ◽

Cited By ~ 1

Author(s):

Haitao Lang ◽

Liren Liu ◽

Qingguo Yang

Keyword(s):

Three Dimensional ◽

Coded Aperture ◽

Imaging Method ◽

Three Dimensional Imaging ◽

Coded Aperture Imaging

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ISAR Autofocus Imaging Algorithm for Maneuvering Targets Based on Phase Retrieval and Keystone Transform

International Journal of Antennas and Propagation ◽

10.1155/2019/8781979 ◽

2019 ◽

Vol 2019 ◽

pp. 1-11 ◽

Cited By ~ 1

Author(s):

Hongyin Shi ◽

Ting Yang ◽

Yue Liu ◽

Jingjing Si

Keyword(s):

Rotational Motion ◽

Phase Retrieval ◽

Translational Motion ◽

Retrieval Algorithm ◽

Imaging Method ◽

Keystone Transform ◽

Maneuvering Targets ◽

Coherent Integration ◽

Motion Parameters ◽

Phase Retrieval Algorithm

In the current scenario of high-range resolution radar and noncooperative target, the rotational motion parameters of the target are unknown and migration through resolution cells (MTRC) is apparent in the obtained inverse synthetic aperture radar (ISAR)images, in both slant-range and cross-range directions. In the case of the high-speed maneuvering target with a small value of rotation, the phase retrieval algorithm can be applied to compensate for the translational motion to form an autofocusing image. However, when the target has a relatively large rotation angle during the coherent integration time, phase retrieval method cannot get an acceptable image for viewing and analysis as the location of the scatterer will not be true due to the Doppler shift imposed by the target’s rotational motion. In this paper, a novel ISAR imaging method for maneuvering targets based on phase retrieval and keystone transform is proposed, which can effectively solve the above problems. First, the keystone transform is used to solve the MTRC effects caused by the rotation component. Next, phase errors caused by the remaining translational motion will be removed by employing phase retrieval algorithm, allowing the scatterers are always kept in their range cells. Finally, the Doppler frequency shifts of scatterers will be time invariant in the phase of the received signal. Furthermore, this approach does not need to estimate the motion parameters of the target, which simplifies the processing steps. The simulated results demonstrate the validity of this method.

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Non-Stationary Platform Inverse Synthetic Aperture Radar Maneuvering Target Imaging Based on Phase Retrieval

Sensors ◽

10.3390/s18103333 ◽

2018 ◽

Vol 18 (10) ◽

pp. 3333 ◽

Cited By ~ 1

Author(s):

Hongyin Shi ◽

Saixue Xia ◽

Qi Qin ◽

Ting Yang ◽

Zhijun Qiao

Keyword(s):

Synthetic Aperture Radar ◽

Phase Retrieval ◽

Experimental Simulation ◽

Synthetic Aperture ◽

Retrieval Algorithm ◽

Imaging Method ◽

Inverse Synthetic Aperture Radar ◽

Maneuvering Target ◽

Motion Parameters ◽

Aperture Radar

As a powerful signal processing tool for imaging moving targets, placing radar on a non-stationary platform (such as an aerostat) is a future direction of Inverse Synthetic Aperture Radar (ISAR) systems. However, more phase errors are introduced into the received signal due to the instability of the radar platform, making it difficult for popular algorithms to accurately perform motion compensation, which leads to severe effects in the resultant ISAR images. Moreover, maneuvering targets may have complex motion whose motion parameters are unknown to radar systems. To overcome the issue of non-stationary platform ISAR autofocus imaging, a high-resolution imaging method based on the phase retrieval principle is proposed in this paper. Firstly, based on the spatial geometric and echo models of the ISAR maneuvering target, we can deduce that the radial motion of the radar platform or the vibration does not affect the modulus of the ISAR echo signal, which provides a theoretical basis for the phase recovery theory for the ISAR imaging. Then, we propose an oversampling smoothness (OSS) phase retrieval algorithm with prior information, namely, the phase of the blurred image obtained by the classical imaging algorithm replaces the initial random phase in the original OSS algorithm. In addition, the size of the support domain of the OSS algorithm is set with respect to the blurred target image. Experimental simulation shows that compared with classical imaging methods, the proposed method can obtain the resultant motion-compensated ISAR image without estimating the radar platform and maneuvering target motion parameters, wherein the fictitious target is perfectly focused.

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Antenna Phase Error Compensation for Terahertz Coded-Aperture Imaging

Electronics ◽

10.3390/electronics9040628 ◽

2020 ◽

Vol 9 (4) ◽

pp. 628

Author(s):

Xingyue Liu ◽

Chenggao Luo ◽

Fengjiao Gan ◽

Hongqiang Wang ◽

Long Peng ◽

...

Keyword(s):

Error Compensation ◽

Phase Error ◽

Radar System ◽

Coded Aperture ◽

Aperture Antenna ◽

Imaging Radar ◽

Phase Errors ◽

Coded Aperture Imaging ◽

Imaging Model ◽

Antenna Phase

Coded-aperture antenna plays an important role in terahertz coded-aperture imaging radar system. However, the performance of a system is inevitably affected by the phase errors introduced by the coded-aperture antenna elements. In this paper, we propose a phase error compensation method by deducing a formula to compute all element phase errors accurately. According to the formula, the phase errors can be calibrated by using a calibrator and can be used to compensate the imaging model of the system. Numerical simulations demonstrate that the proposed method can effectively improve the imaging quality when the elemental phase error exceeds 10 ∘ .

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A Simply Equipped Fourier Ptychography Platform Based on an Industrial Camera and Telecentric Objective

Sensors ◽

10.3390/s19224913 ◽

2019 ◽

Vol 19 (22) ◽

pp. 4913

Author(s):

Shaohui Zhang ◽

Guocheng Zhou ◽

Ying Wang ◽

Yao Hu ◽

Qun Hao

Keyword(s):

Phase Retrieval ◽

Dynamic Range ◽

Numerical Aperture ◽

Complementary Metal Oxide Semiconductor ◽

Computational Imaging ◽

Field Of View ◽

Oxide Semiconductor ◽

Imaging Method ◽

Wide Field ◽

Wide Field Of View

Fourier ptychography microscopy (FPM) is a recently emerged computational imaging method, which combines the advantages of synthetic aperture and phase retrieval to achieve super-resolution microscopic imaging. FPM can bypass the diffraction limit of the numerical aperture (NA) system and achieve complex images with wide field of view and high resolution (HR) on the basis of the existing microscopic platform, which has low resolution and wide field of view. Conventional FPM platforms are constructed based on basic microscopic platform and a scientific complementary metal–oxide–semiconductor (sCMOS) camera, which has ultrahigh dynamic range. However, sCMOS, or even the microscopic platform, is too expensive to afford for some researchers. Furthermore, the fixed microscopic platform limits the space for function expansion and system modification. In this work, we present a simply equipped FPM platform based on an industrial camera and telecentric objective, which is much cheaper than sCMOS camera and microscopic platform and has accurate optical calibration. A corresponding algorithm was embedded into a conventional FP framework to overcome the low dynamic range of industrial cameras. Simulation and experimental results showed the feasibility and good performance of the designed FPM platform and algorithms.

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