Search

MC-GPU is a GPU-based Monte Carlo simulator that realizes enhanced computational speeds by exploiting the parallelism of the GPU architecture. Although MC-GPU is capable in theory of modeling XRD imaging systems, existing MC-GPU configurations are limited to simulating water or water-like materials. Here, we demonstrate MC-GPU's ability to rapidly simulate arbitrary materials and model real-world experimental X-ray diffraction (XRD) imaging systems. We found a mean-squared error (MSE) < 1.50E-02 and cross-correlation (CC) > 0.99 (with a speed-up of 1075x for MC-GPU compared to GEANT4) for all comparisons in the unit-testing/cross-validation phase. Additionally, we showcased MC-GPU's ability to model realistic experimental systems by modelling a fan beam coded aperture XRD imaging system. These results demonstrate MC-GPU's utility in rapidly simulating complex, real-world XRD imaging systems, which is critical in applications ranging from medical to security imaging. [ABSTRACT FROM AUTHOR]

The novel rotating synthetic aperture imaging system has the advantages of short processing cycle, light weight, low cost, and convenient transport, which is a potential development direction for future optical satellite payloads with ultra-large aperture. However, influenced by the coupling effects of the rectangular primary mirror, rotating imaging, and link perturbation, images from this system may have unique spatial and temporal variability with resolution anisotropy, resulting in the dynamics and weak features of targets. The insufficient recognition of system characteristics seriously restricts the application ability of corresponding target interpretation methods. To address this problem, we start with the analysis of system imaging characteristics and target interpretation mechanisms. Considering calculating texture, grayscale, and edge feature parameters in evaluation regions of different sizes, we propose a degradation assessment method based on multi-scale feature characterization. Then, combined with the theoretical calculation and practical target detection experiments, the influence of crucial parameters such as the aspect ratio and rotation angle of the primary mirror on the target interpretation capability is analyzed. The results will provide guidance for the integrated design and optimization of optical imaging systems and intelligent image processing methods. • A degradation assessment method based on multi-scale feature characterization is proposed. • The effect of rotating synthetic aperture system on image target characteristic degradation is analyzed. • The impacts of key system parameters on target detection performance are analyzed. [ABSTRACT FROM AUTHOR]

• A high-speed, high-efficiency solution utilizing phase-change materials (PCM) within a metal-dielectric-metal (MDM) nano-cavity configuration method. • Our 4-layer nano cavity, ∼600 nm thin metal-dielectric cavity offers dynamic switching between bright-field (low pass filtering) and dark-field (high pass filtering) modes. Enhancing optical imaging, it provides essential morphological information. • Pioneering the application of nano-photonics devices in reflection mode for optical analog computing, demonstrated through experimental schemes involving interferometry setups, offering potential applications in biomedical imaging, computer vision, and artificial intelligence. A combination of optical analog computing and nanophotonic design is attractive due to its fast-processing times, large data processing rates, and high integration with modern imaging systems. However, most of the proposed nano-photonics designs for this purpose have static functionality, which limits their applicability. By modulating the Green's function response of the thin film nanocavity using phase change properties of S b 2 S 3 , we propose tunable bright and dark-field imaging. We optimize the nano-cavity for the bright field in a crystalline and dark field in the amorphous phase of S b 2 S 3. The proposed design shows a near-unity numerical aperture which enables the resolution of the system to ∼500 nm. Lastly, we examine the potential integration of this cavity into a standard interferometric setup and scattering microscopy, leveraging the tunable modulation capability of the proposed cavity as a substrate in reflection mode scheme. This ultrathin, on-chip, and real-time tunable lithographic-free imaging system can play a crucial role in a host of applications such as machine vision, medical imaging, and sensing. [ABSTRACT FROM AUTHOR]

Rotating Synthetic Aperture (RSA) technology is one of the distinctly advantageous Earth geostationary orbit optical remote sensing technologies. However, the continuous rotation of the RSA system's rectangular primary mirror results in a discernible drop in resolution along the shorter side of the mirror. Additionally, the captured images exhibit periodic and time-varying characteristics. To improve the image quality to meet interpretation needs, we first delineate the imaging process of the rotating primary mirror and analyze the characteristics of image degradation based on the system's imaging mechanism. Then, we propose a dual super-resolution (SR) framework based on Swin Transformer and introduce a self-supervised learning method for jointly training the unified SR network using wavelet fusion. The self-supervised learning method effectively utilizes the spatiotemporal correlation of the information contained in images captured at different rotation directions of the rectangular pupil. Moreover, the attention mechanism in Transformer can adopt a global perspective and utilize content-based interactions between image content and attention weights to model strong long-range dependencies in remote sensing images. This approach significantly enhances image quality along the pupil's shorter side, consequently yielding superior results. Extensive digital and semi-physical imaging experiments, involving six aspect ratios of the primary mirror, demonstrate that our SR method surpasses state-of-the-art methods. The work in this paper can serve as a valuable reference for future space applications of the RSA technology. • Analyzing the imaging mechanisms of the rotating synthetic aperture system. • Self-supervised learning enhances the utilization of image internal information. • Designing a dual framework that can be trained jointly for image super resolution. • Interactions between image content and attention weights improve performance. • Performance is evaluated through digital and semi-physical experiments. [ABSTRACT FROM AUTHOR]

• Analyzing the imaging characteristics of the rotating synthetic aperture system. • Intra-frame self-attention enhances the utilization of spatial information. • Inter-frame mutual attention enhances the utilization of temporal information. • Interactions between image content and attention weights improve performance. • Performance is evaluated through digital and semi-physical experiments. Rotating synthetic aperture (RSA) technology offers a promising solution for achieving large-aperture and lightweight designs in optical remote-sensing systems. It employs a rectangular primary mirror, resulting in noncircular spatial symmetry in the point-spread function, which changes over time as the mirror rotates. Consequently, it is crucial to employ an appropriate image-fusion method to merge high-resolution information intermittently captured from different directions in the image sequence owing to the rotation of the mirror. However, existing image-fusion methods have struggled to address the unique imaging mechanism of this system and the characteristics of the geostationary orbit in which the system operates. To address this challenge, we model the imaging process of a noncircular rotating pupil and analyse its on-orbit imaging characteristics. Based on this analysis, we propose an image-fusion network based on a vision transformer. This network incorporates inter-frame mutual attention and intra-frame self-attention mechanisms, facilitating more effective extraction of temporal and spatial information from the image sequence. Specifically, mutual attention was used to model the correlation between pixels that were close to each other in the spatial and temporal dimensions, whereas long-range spatial dependencies were captured using intra-frame self-attention in the rotated variable-size attention block. We subsequently enhanced the fusion of spatiotemporal information using video swin transformer blocks. Extensive digital simulations and semi-physical imaging experiments on remote-sensing images obtained from the WorldView-3 satellite demonstrated that our method outperformed both image-fusion methods designed for the RSA system and state-of-the-art general deep learning-based methods. 1 1 Dataset is available at https://github.com/sherlockyusun/RSA-Fuse. [ABSTRACT FROM AUTHOR]

Optical sparse aperture imaging technology has promising applications in the next generation of high-resolution imaging systems, but the phasing errors correction of sparse aperture is an urgent problem to be addressed. In this paper, we propose a blind structured-illumination super-resolution imaging system using a sparse aperture as the transmitter to overcome phasing errors and obtain higher resolution. In our scheme, an unknown pattern is projected onto the object by a sparse aperture system. By translating the unknown pattern, a sequence of modulated raw images is obtained. Based on these low-resolution raw images, the super-resolution object and the unknown illumination pattern are jointly estimated by the Adam algorithm. Here we show, both in the simulation and experiment, the resolution of reconstructions using sparse aperture as transmitter are similar to those using monolithic lens. Furthermore, we validate that the proposed method can protect the reconstruction effect from piston error and widen the tolerance range of tip/tilt error (peak-valley values) up to 0.5λ. At the same time, our proposed system can also alleviate to some extent the problem of mid-frequency modulation transfer function (MTF) attenuation that exists in sparse aperture imaging. Our approach not only simplifies the process of constructing synthetic aperture system, but also provides a novel application for synthetic aperture systems. • The introduction of structured illumination improves the resolution of synthetic aperture imaging. • Protect the reconstruction effect from piston error in the sparse aperture transmitter. • Widen the tolerance range for imaging system of tip/tilt error in sparse aperture transmitter. • Alleviate to some extent the problem of mid-frequency attenuation that exists in sparse aperture imaging. [ABSTRACT FROM AUTHOR]

• Holographic images can be combined coherently to increase image resolution and field of view. • The choice of illumination and observation geometries affect the point-spread and transfer characteristics of the imaging system. • Phase contrast imaging in transmission and reflection geometries is possible. This paper discusses a modular implementation of synthetic aperture interferometry (SAI) using inexpensive telecommunications technologies that can be expanded for use in optical instruments with arbitrarily large fields of view. Exploiting multiple image sensors and multiple illumination sources, transmission and reflection SAI geometries, capable of emulating the phase contrast and interference modes of conventional interference microscopes, are considered. The point-spread and transfer characteristics of these geometries are illustrated for the case of a transmission mode instrument. It is shown that although imaging is strictly field dependent (i.e. shift-variant), the response of modular instruments is periodic and with careful choice of illumination and sensor positioning can be made quasi shift-invariant. We demonstrate SAI in a transmission configuration comprising of a single coherent imager that holographically records the field scattered from a test target sequentially illuminated by 16 different plane waves. This set-up is equivalent to a single module of a larger SAI system and since brightfield regions in the individual reconstructed images overlap, provides an ideal platform to examine the effect of tilt and phase offset errors in the illumination. By applying a first order correction and assuming phase continuity over the overlapping regions, we demonstrate a significant improvement in the SAI reconstruction. [ABSTRACT FROM AUTHOR]

In a sparse aperture imaging system, the piston error affects the co-phase of subapertures and reduces the imaging resolution. Based on the image quality evaluation function, the piston error correction can be converted into a class of optimization problems. In this paper, a metaheuristic algorithm is used to implement global search based on stochastic parallel gradient descent algorithm. A hybrid algorithm is obtained by combining the stochastic parallel gradient descent algorithm with the Gray Wolf algorithm. The hybrid algorithm is developed at the best three positions of the population (the head wolf) using the gradient direction of the SPGD algorithm, and the other populations keep moving toward the best three head wolves. This hybrid algorithm balances exploration and exploitation better in the piston error correction of sparse aperture systems. The hybrid algorithm has a good optimization speed while satisfying the correction accuracy. The performance of this hybrid algorithm is verified in simulations with three-aperture and seven-aperture systems. • A hybrid algorithm is obtained by combining the stochastic parallel gradient descent algorithm with the Gray Wolf algorithm. • The hybrid algorithm balances exploration and exploitation better in the piston error correction of sparse aperture systems. [ABSTRACT FROM AUTHOR]

Condition assessment of masonry structures is important for maintaining their safety and durability. In this paper, a 10-GHz synthetic aperture radar (SAR) imaging system is proposed for assessing the condition of brick specimens. Three brick specimens of different sizes were manufactured and imaged remotely by the SAR system inside an anechoic chamber at different ranges (from 0.4 m to 0.9 m). Empirical models for ranging, sizing and predicting dielectric constant of brick specimens were developed from the SAR images. Range, size, and dielectric constant of a brick specimen can be calculated from the amplitudes and distribution from its SAR image. [ABSTRACT FROM AUTHOR]

Abstract Inverse synthetic aperture imaging lidar is a new active imaging system, which can offer a finer azimuth resolution than that achieved in conventional SAR system and obtain vivid images close to the optical photos. Firstly, the principle of the inverse synthetic aperture techniques is described. Secondly, after analyzing the data of the inverse synthetic aperture imaging lidar, the mathematic model of the data is given. Thirdly, a method, combined with "CLEAN" techniques, is proposed for inverse synthetic aperture imaging lidar processing, which is based on the analysis of data's time-frequency character. The presented method uses the second-order phase of the data in azimuth, estimates the instantaneous Doppler spectrum and obtains the instantaneous images in the range and the instantaneous Doppler domains, which can avoid the defocusing of the images using the range Doppler algorithm and improve the imaging quality. Finally, the data processing of the real data proves the validity of the given method. [ABSTRACT FROM AUTHOR]

Highlights • DB-SAT yields better, and depth independent, lateral resolution compared to CFB. • The frame –rate achievable using DB-SAT is several times more compared to CFB. • DB-SAT with only 8-TX/64-RX elements achieved the above characteristics. Abstract In this paper, a technique combining Diverging Beam with Synthetic Aperture Technique (DB-SAT) is demonstrated that utilizes only limited number of active elements yet provides better quality images at higher frame rates than possible with Conventional Focused Beamforming (CFB). The DB-SAT has been investigated in simulations and experiments on wire and tissue-mimicking phantoms, and the results are compared with routinely used CFB with Linear Array (CFB-LA). The estimated lateral resolution at the focal point was 0.41 mm and 0.34 mm for CFB-LA and DB-SAT, respectively, in simulations. These were estimated to be 0.78 mm and 0.71 mm, respectively, in experiments. Experimentally computed contrast resolution (contrast-to-noise ratio) for the cyst located at 60 mm depth were 0.50 (1.31 dB) and 0.58 (2.33 dB) for CFB-LA and DB-SAT, respectively. The frame-rate achieved by DB-SAT was 8 times and 2 times higher than that achieved by CFB-LA when transmit sub-apertures had an overlap 0% and 75%, respectively. Therefore, it can be concluded from the results that DB-SAT using 8 active transmit elements and 64 active receive elements yields better quality images at higher frame-rates than those obtained using CFB-LA with 64 active elements in transmit and receive. Since there is a reduction in the number of active transmit elements in the case of DB-SAT, it leads to a reduction in the overall system complexity. [ABSTRACT FROM AUTHOR]

Abstract The Phased Array Ultrasonic Technique (PAUT) offers great advantages over the conventional ultrasound technique (UT), particularly because of beam focusing, beam steering and electronic scanning capabilities. However, the 2D images obtained have usually low resolution in the direction perpendicular to the array elements, which limits the inspection quality of large components by mechanical scanning. This paper describes a novel approach to improve image quality in these situations, by combining three ultrasonic techniques: Phased Array with dynamic depth focusing in reception, Synthetic Aperture Focusing Technique (SAFT) and Phase Coherence Imaging (PCI). To be applied with conventional NDT arrays (1D and non-focused in elevation) a special mask to produce a wide beam in the movement direction was designed and analysed by simulation and experimentally. Then, the imaging algorithm is presented and validated by the inspection of test samples. The obtained images quality is comparable to that obtained with an equivalent matrix array, but using conventional NDT arrays and equipments, and implemented in real time. [ABSTRACT FROM AUTHOR]

Large-aperture optical components have a wide application in high-power laser facilities. Surface flaws such as damages and contaminants generated under high-power laser irradiation can greatly affect the optical or mechanical performance of optics, so the optical components must be carefully inspected to evaluate optics damage and cleanliness. However, it is of great challenge to achieve rapid and accurate positioning, classification, and measurement of micron-level flaws on the surface of large-aperture optics. This paper proposes a novel surface flaw detection technology based on machine vision and machine learning. To balance efficiency and accuracy, a dark-field imaging system based on progressive scanning is designed to obtain the image of optics surface. A set of surface flaw detection algorithms based on machine learning including object segmentation, flaw feature extraction, and classification and size calibration of flaw are proposed to accurately assess the state of surface flaws. The experiments show that the system can complete the detection of an optical component (430 mm × 430 mm) within 6 min. The minimum detectable size of the flaws can reach 20 μm, and the position accuracy of the flaws is better than 50 μm. The classification accuracy of flaw is 98.59 %, and the average relative errors of the size measurement of damages and contaminants are 3.23 % and 6.58 %, respectively. The experimental results demonstrate the effectiveness of the method in detecting surface flaws of large-aperture optics. [ABSTRACT FROM AUTHOR]

• An ultra-compact add-on module (about 30 mm in total) based on two polarization gratings is built for single shot DIC type quantitative phase imaging. • A fast sythethis aperture (line-scanning) method is proposed. • The zdirectional sectional ability of 3D phase imaging is discuused in the supplementary material and several important conlusions are made. Differential interference contrast (DIC) microscopy is an important member of quantitative phase imaging (QPI) family owing to its simple optical implementation and high compatibility regarding to different coherence degree of illumination field. Such compactivity means that the DIC-based phase imaging can be conveniently converted between 2D-integrational and 3D-sectional modes by switching the spatial coherence degree of illumination field between low degree and high. However, there is a potential trade-off compromise in the existed experimental implementations for DIC imaging regarding to the optical simplicity, space-bandwidth utilization and temporal resolution. In this manuscript, we proposed a polarization gratings pair (PGs) based off-axis DIC system to realize integrational and sectional QPI. Building on a bright field microscope and getting rid of the additional 4f lens system, the proposed PGs-DIC system can realize single-shot QPI with an ultra-compact optical configuration. In order to improve the imaging resolution and optical sectional ability, a fast synthetic aperture technology is introduced, in which multiple interferograms with different line-filtered illumination are captured. Both high resolution 2D-integrational and 3D-sectional phase imaging results indicate that the proposed PGs-DIC system is a good candidate for QPI. Specially, a theoretical model is proposed to quantitatively estimate z-direction resolution for z -scanning 3D phase imaging technology and future application in the PGs-DIC system. [ABSTRACT FROM AUTHOR]

Multiple-aperture SAR interferometry (MAI) is an advanced technique that is used to retrieve actual surface motions by complementing missing components of InSAR measurements. Despite the wide use of the MAI method in the geosciences, X-band SAR has rarely been applied in MAI-based studies due to the relatively shorter decorrelation periods involved. Thus, we need to evaluate the MAI measurements from X-band SAR for the use in the geosciences. In this paper, an assessment of the MAI performance for TerraSAR-X system was carried out at the test site, Kīlauea Volcano, Hawaii, focusing on the Kamoamoa fissure eruption episode that occurred on March 6–10, 2011. The root-mean-square (RMS) errors of single MAI interferograms were 3.26 ± 1.32 cm and 2.95 ± 0.77 cm for descending and ascending datasets, respectively. Multi-stacked MAI interferograms showed reduced error levels of 1.77 and 2.04 cm for descending and ascending datasets, respectively. In addition, empirical uncertainty models of the MAI measurements were generated with respect to the interferometric coherence of single- and multi-stacked MAI measurements, and these regression models enabled us to confirm the difference between the theoretical and practical accuracies of the MAI measurements. Moreover, the MAI-based 3D model based on high accuracy 3D maps showed some possibilities of new findings and interpretations of the geologic sources. [ABSTRACT FROM AUTHOR]

The resolution of a conventional optical imaging radar system is constrained by the diffraction limit of the telescope's aperture. The combination of lidar and synthetic aperture processing techniques can overcome the diffraction limit and provide a higher resolution air borne remote sensor. Atmospheric turbulence is an important factor affecting lidar imaging, and the phase screen simulation method is an effective method to simulate the degradation of laser signal propagating through turbulent atmosphere. By using Monte-Carlo random factor, the randomness of phase screens can be improved. The lidar imaging with different turbulence intensity is also calculated in this paper, then the improved rank one phase estimation autofocus method is used to compensate the imaging phase errors. The results show that the method of generating phase screen is consistent with the statistics of atmospheric turbulence, which can well simulate the effect of atmospheric turbulence on synthetic aperture lidar, and the influence on synthetic aperture lidar azimuth resolution is greater when atmospheric turbulence is stronger. Improved rank one phase estimation algorithm has good autofocus effect, which can effectively compensate the phase errors and enhance the image quality degraded by turbulence. [ABSTRACT FROM AUTHOR]

• The current Fourier ptychographic imaging need high aperture overlapping ratio to ensure the convergence. This limitation dictates that the images can only be acquired by dense aperture scanning. We proposed a new framework to solve the Fourier ptychographic imaging with sparse aperture. Our method breaks the limitation of dense aperture scanning and allows multiple separate imaging systems to capture images simultaneously, which could simplify the imaging configuration and improve the acquisition efficiency. • In our work, the aperture overlapping ratio is reduced to less than 25% for the first time. The imaging quality of proposed method also outperforms than the state-of-the-art methods under the same imaging parameters. Our work shows the potential for single-shot imaging by using a camera array instead of aperture scanning mentioned in previously published works, so that the observation of rapidly changing scenes can be realized. Synthetic aperture technique could effectively expand the passband and beyond the diffraction limit of aperture. Macroscopic Fourier ptychography (FP) makes synthetic aperture feasible in visible light by incorporating phase retrieval process into synthetic aperture. In FP, a dense aperture sampling is necessary to overcome the ill-posedness of phase retrieval, which leads to long acquisition time and heavy computation. Here, a total variation regularization-based Fourier ptychographic (TVFP) reconstruction method is proposed for long-range imaging. The TVFP method imposes total variation constraints to improve the ill-posedness of the imaging model, and recovers high-quality image from sparse aperture sampling. For the imaging system with aberration, a joint optimization of pupil function and target image is also proposed to achieve the aberration free image and the estimated pupil function simultaneously. The results show the aperture overlapping ratio could be reduced to 25% or less. The proposed method simplifies the imaging configuration and improves the robustness for long-range imaging. [Display omitted] [ABSTRACT FROM AUTHOR]

We analyze interferometric synthetic aperture radar (InSAR) data acquired between 2004 and 2014, by the ERS-2, Envisat, ALOS and TerraSAR-X/TanDEM-X satellite missions to measure and characterize time-dependent deformation at the Brady Hot Springs geothermal field in western Nevada due to extraction of fluids. The long axis of the ∼4 km by ∼1.5 km elliptical subsiding area coincides with the strike of the dominant normal fault system at Brady. Within this bowl of subsidence, the interference pattern shows several smaller features with length scales of the order of ∼1 km. This signature occurs consistently in all of the well-correlated interferometric pairs spanning several months. Results from inverse modeling suggest that the deformation is a result of volumetric contraction in shallow units, no deeper than 600 m, likely associated with damaged regions where fault segments mechanically interact. Such damaged zones are expected to extend downward along steeply dipping fault planes, providing a high permeability conduit to the production wells. Using time series analysis, we test the hypothesis that geothermal production drives the observed deformation. We find a good correlation between the observed deformation rate and the rate of production in the shallow wells. We also explore mechanisms that could potentially cause the observed deformation, including thermal contraction of rock, decline in pore pressure and dissolution of minerals over time. [ABSTRACT FROM AUTHOR]

The dune field intersected by the Israel–Egypt borderline has attracted many remote sensing studies over the years because it exhibits unique optical phenomena in several domains, from the visual to the thermal infrared. These phenomena are the result of land-use policies implemented by the two countries, which have differing effects on the two ecosystems. This study explores the surface properties that affect radar backscatter, namely the surface roughness and dielectric properties, in order to determine the cause for the variation across the border. The backscatter contrast was demonstrated for SIR-C, the first synthetic aperture radar (SAR) sensor to capture this phenomenon, as well as ASAR imagery that coincides with complementary ground observations. These field observations along the border, together with an aerial image from the same year as the SIR-C acquisition were used to analyze differences in vegetation patterns that can affect the surface roughness. The dielectric permittivity of two kinds of topsoil (sand, biocrust) was measured in the field and in the laboratory. The results suggest that the vegetation structure and spatial distribution differ between the two sides of the border in a manner that is consistent with the radar observations. The dielectric permittivity of sand and biocrust was found to be similar, although they are not constant across the radar spectral region (50 MHz–20 GHz). These findings support the hypothesis that changes to the vegetation, as a consequence of the different land-use practices in Israel and Egypt, are the cause for the radar backscatter contrast across the border. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) step parallel confocal image processing algorithm for synthetic aperture imaging ladar (SAIL) is proposed. The feature of the algorithm is the collected data are confocal imaged in space domain by 2D Fourier transform. The collected data are first expressed by separation of variables and time-domain data are translated into a spatial coordinate expression suitable for space optical conversion, compensated with an azimuth quadratic phase and then imaged in space domain by 2D Fourier transform. Functions of the algorithm for SAIL with rectangular apertures is described and analyzed in terms of continuous variables and functions. Then the position of the imaging point is given. The technique is a new, one-step confocal imaging method for ladar echo signal. The confocal image processing is simplified and the imaging time is shortened. The requirement of a ladar image processing system is also reduced. It has a significant advantage in the data processing of synthetic-aperture ladar target echo confocal imaging. [ABSTRACT FROM AUTHOR]

Using elastic-wave-based NDT methods to detect defects in RC structures is difficult because of the interference of rebars. In this study, the interference effect on the quality of SAFT images was quantitatively explored using a series of numerical simulations. Furthermore, two concrete specimens were fabricated for experimental verification. The experimental results exhibited strong agreement with those of quantitative analyses used in numerical simulations. These results indicated that using SAFT images to expose the defects under a layer of rebars is feasible. Moreover, a useful guideline for selecting the impacting source to produce a high-quality SAFT image is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Fast decoding algorithms are described for a number of established coded aperture systems. The fast decoding algorithms for all these systems offer significant reductions in the number of calculations required when reconstructing images formed by a coded aperture system and hence require less computation time to produce the images. The algorithms may therefore be of use in applications that require fast image reconstruction, such as near real-time nuclear medicine and location of hazardous radioactive spillage. Experimental tests confirm the efficacy of the fast decoding techniques. [Copyright &y& Elsevier]

Abstract: In recent years, sparse-optical-synthetic-aperture telescope has emerged as an important developing trend for large-scale telescope, where the correction of piston error among different sub-apertures plays an important role for achieving high resolution. The 2π ambiguity effect is the most important aspect of piston error's influences upon system's far-field intensity, which was theoretically analyzed at first. Then the bi-sub-aperture system was taken as an example to test the correctness of the theoretical model through distributions of the system's far-field intensity. In addition, a theoretical proof was made to get some important properties of piston errors within such kind of system. From the results, it is shown that the 2π ambiguity comes along with any piston error in the system, and this effect stands independent for different piston errors between different pair of sub-apertures. The derivation also provides effective theoretical model for related concerns within such kind of system. [Copyright &y& Elsevier]

Highlights: [•] Airborne 3-D volumetric imaging system based on capacitive micromachined ultrasonic transducers. [•] A 26×26 2-D array implemented by using the classic synthetic aperture method. [•] Measured lateral resolution (3.17°) agrees with theoretical point spread function. [•] The 3-D imaging of two plates at a distance of 350mm and 400mm is constructed. [ABSTRACT FROM AUTHOR]

Highlights: [•] A technique for imaging of contact acoustic nonlinearity at closed interfaces was developed. [•] Variation in the second harmonic magnitude at the contact interfaces as the contact pressure was visualized. [•] Variation in the acoustic nonlinear parameter at the contact interfaces as the contact pressure was visualized. [•] This technique will be useful to detect the closed cracks and improve the sizing accuracy. [Copyright &y& Elsevier]

The blur is a problem impacting the image quality of optical synthetic aperture imaging (OSAI) system and requiring image restoration techniques for deconvolution. However, most traditional image deconvolution algorithms are non-blind methods and also highly susceptible to the unknown noise. The turbulence perturbation and the co-phase error are both factors that may affect the recovery performance. As for the image restoration under noises and turbulence correction error, a further optimized network named as RestoreNet-Plus is designed. After further optimization, RestoreNet-Plus has advantages as below: • Blind restoration ability and generalization capacity: RestoreNet-Plus could remove the blur better in the blind way facing different targets through OSAI system; • Anti-noise ability: It could beat other methods under different levels noises, including Wiener filter, Hyper-Laplacian prior algorithm, Lucy-Richardson algorithm, Blind Deconvolution algorithm and RestoreNet. • Anti-turbulence correction error ability: RestoreNet-Plus could maintain good Blind restoration ability under the influence of turbulence correction error in imaging. • Fast for applying: RestoreNet-Plus performances the best in the image restoration of OSAI system under noises and turbulence correction error with only 54 ms time costs. The synthetic aperture technology can improve the resolution effectively in the optical imaging system. In fact, the imaging blur, turbulence aberration and noise can affect the imaging quality of optical synthetic aperture imaging system seriously. Several non-blind methods are applied generally to recover the degraded maps with the prior information. However, the restoration effect is not stable enough and satisfactory. As a data-driven approach, the deep learning framework possesses advantages in solving this problem. In this paper we propose an improved network, RestoreNet-Plus, for the image restoration of optical synthetic aperture imaging system. After the proofs of numerical simulation and experiment results, RestoreNet-Plus is a better alternative compared with other methods, owing to its better restoration ability, strong denoising ability and capacity for turbulence correction error. [ABSTRACT FROM AUTHOR]

Abstract: Synthetic aperture imaging using an array of cameras, which has become popular recently, can easily handle the occlusion problem by “seeing through” occluders. Unfortunately, the resulting image is still blurry because it combines information not only from the region of interest but also from the occluding regions. Removing the blurriness of synthetic aperture images has become a challenging task for many computer vision applications. In this paper, we propose a novel method to improve the image quality of synthetic aperture imaging using energy minimization. Unlike the conventional synthetic aperture imaging method, which averages images from all the camera views, we reformulate the problem as a labeling problem. In particular, we use the energy minimization method to label each pixel in each camera view to decide whether or not it belongs to an occluder. After that, the focusing at the desired depth is by averaging pixels that are not labeled as occluder. The experimental results show that the proposed method outperforms the traditional synthetic aperture imaging method as well as its improved versions, which are simply dim and blur occluders in the resulting image. To the best of our knowledge, our proposed method is the first one for improving the results of synthetic aperture image without using a training set from the input sequence. As well, it is the first method that makes no assumptions on whether or not the objects in the scenes are static. [Copyright &y& Elsevier]

Abstract: This paper proposes a novel multi-object detection method using multiple cameras. Unlike conventional multi-camera object detection methods, our method detects multiple objects using a linear camera array. The array can stream different views of the environment and can be easily reconfigured for a scene compared with the overhead surround configuration. Using the proposed method, the synthesized results can provide not only views of significantly occluded objects but also the ability of focusing on the target while blurring objects that are not of interest. Our method does not need to reconstruct the 3D structure of the scene, can accommodate dynamic background, is able to detect objects at any depth using a new synthetic aperture imaging method based on a simple shift transformation, and can see through occluders. The experimental results show that the proposed method has a good performance and can synthesize objects located within any designated depth interval with much better clarity than that using an existing method. To our best knowledge, it is the first time that such a method using synthetic aperture imaging has been proposed and developed for multi-object detection in a complex scene with a significant occlusion at different depths. [Copyright &y& Elsevier]

Abstract: A new functional model for determining the minimum and maximum detectable deformation gradients of interferometric synthetic aperture radar (InSAR) is developed. The model incorporates both the interferometric coherence and the look number, representing an extension to the existing models that consider only the interferometric coherence. Experimental results with Envisat ASAR data show that the new model performs well for interferograms with different look numbers and interferometric coherences. The model can serve as an important tool in determining whether InSAR technology can be used effectively to monitor a particular ground deformation. In addition, the model can also be used to determine the optimum look number for multi-looking operations to result in the best deformation monitoring results. [Copyright &y& Elsevier]

Abstract: Image formation in focal modulation microscopy using quadrant apertures (QFMM) is presented. The spatial resolution is discussed: compared with confocal microscopy, QFMM can simultaneously enhance the axial and transverse resolution. In contrast to focal modulation microscopy using D-shaped apertures (DFMM), QFMM can maintain x–y symmetry of spatial resolution, thus causing less confusion in imaging interpretation. The capability of background rejection is investigated, showing QFMM has the potential to increase imaging penetration depth. The signal level is also analyzed, indicating that the preferred detector pinhole radius is greater than for DFMM, resulting in a higher signal level. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated changes in cortical oscillations following congruent and incongruent grapheme–phoneme stimuli. Hiragana graphemes and phonemes were simultaneously presented as congruent or incongruent audiovisual stimuli to native Japanese-speaking participants. The discriminative reaction time was 57ms shorter for congruent than incongruent stimuli. Analysis of MEG responses using synthetic aperture magnetometry (SAM) revealed that congruent stimuli evoked larger 2–10Hz activity in the left auditory cortex within the first 250ms after stimulus onset, and smaller 2–16Hz activity in bilateral visual cortices between 250 and 500ms. These results indicate that congruent visual input can modify cortical activity in the left auditory cortex. [Copyright &y& Elsevier]

Abstract: The vectorial modification of Kirchhoff approach is proposed for the calculation of the diffracted electromagnetic field in the vicinity of small apertures in thin metal and black screens. [Copyright &y& Elsevier]

Optical vortices in focal regions are studied using the Debye approximation. We discuss how scalar vortices give rise to different intensity structures in the focal region for a certain class of apertures. Vortices in cylindrical symmetric polarization distributions form new complex structures in the focal region, and in some cases the intensity is no longer zero on the optical axis. In particular, we find that for an azimuthal polarization distribution the local circulation deviates from that of the vortex impinging on the lens. On the other hand, upon using a radially polarized field distribution combined with an annular aperture, only the electric-field component along the optical axis remains, and the field structure is the same as in the scalar case. [Copyright &y& Elsevier]

After generating the first femto-second X-ray pulses at the Advanced Light Source (ALS), it becomes critical to improve the flux of this femto-second source for user experiments. A narrow-gap in-vacuum undulator has been proposed to be installed in one of the ALS straight sections. To realize the optimal performance of this undulator, a straight section lattice with a mini vertical beta function has been designed. Separation of electrons has been achieved by generating a sizable vertical dispersion via a local dispersion bump and a closed orbit bump. Particle tracking study shows that the modified ALS lattice for the femto-second X-ray source has an adequate dynamic aperture. [Copyright &y& Elsevier]

• The imaging mechanism of the novel rotating synthetic aperture system is deduced. • The image degradation model of the rotating synthetic aperture system is presented. • The effects of factors causing image quality degradation are analyzed. The Rotating synthetic aperture (RSA) is one of the most promising novel imaging systems to meet the requirements of lightweight and high resolution for optical remote sensing satellites, especially in geostationary orbit. The point spread function (PSF) orientation relative to the observed scene, intentionally changes to measure all spatial frequency information available to a filled circular aperture having a diameter approximately equal to the length of the rectangular aperture. As with all precision optical systems, RSA is also subject to dynamic disturbances from the spacecraft/environment. If not accommodated properly in the measurement and synthesis process, the dynamic disturbances can result in significant image quality degradation. To quantify methods to reduce or eliminate the errors, we first analyze the on-orbit imaging mechanism of the RSA system theoretically and then represent the worst-case on-orbit imaging degradation characteristics. [ABSTRACT FROM AUTHOR]

• A diffusing model and an aliasing-free DOF model were proposed to analyses the influence of the position and diffusing-angle for holographic diffuser based InIm display system. • The larger the diffusing-angle and the farther away from the reconstructed point, the more blurred the reconstructed image will be. • Enhanced aliasing-free depth of field and better viewing effect are achieved, when the holographic diffuser is located at the far-end of the marginal depth plane instead of the traditional central depth plane. The holographic diffuser plays a significant role in the reconstruction performance of the large-size integral imaging display system. However, the influence of the holographic diffuser on the display quality is seldom theoretically analyzed. In this paper, a quantitative beam analysis approach is proposed, and a diffusing model is established to analyses the influence of the position and diffusing-angle of the holographic diffuser on different reconstruction points, then the mechanism of the aliasing effect caused by the holographic diffuser is revealed. Both the numerical and optical experiments are implemented to prove the validity of the established model, and the results are well agreed with the theoretical analysis, which shows that when the holographic diffuser with a certain diffusing-angle is located at the far-end of the marginal depth plane instead of the traditional central depth plane (CDP), the system can obtain an enhanced aliasing-free depth of field and have a better viewing effect, which is inconsistent with the traditional intuition and experience. [ABSTRACT FROM AUTHOR]

• Non-blind algorithms, such as the Wiener filter and the Lucy-Richardson algorithm, are always used to restore images of the optical synthetic aperture imaging (OSAI) system, but can't apply in practice easily due to the unknown prior information of system. Deep learning is a new technology rising nowadays, and has many successful application cases in different fields. An improved U-shaped network named RestoreNet is designed to remove the blur and recover the image from OSAI system. • After enough training, RestoreNet has advantages as below: • Restoring ability : After enough training, RestoreNet can remove the blur definitely and easily in OSAI system; • Fast for applying : In testing period, the recovering time for one image is just ~30ms , but the restoration effect is better than the Lucy-Richardson algorithm, which takes 470ms for one image; • Prior information unknown : RestoreNet can restore images without the prior information of system , for example, the point spread function or the optical transfer function, which is not provided by the non-blind algorithms; • Generalization ability : RestoreNet has strong ability in generalization ability whether facing different types of images or imaging systems with different sub-aperture arrangements. Imaging blur is an inevitable problem in optical synthetic aperture imaging system because of the low response of frequency. Non-blind deconvolution algorithms are usually used for image restoration to obtain clear and high-resolution images. However, accurate prior information on the optical transfer function of system is required in the non-blind methods. As a data-driven approach, recent developments in deep learning have shown great potential in image processing. In this paper, a U-shaped deep learning framework named RestoreNet is proposed for image restoration, especially for removing the blur of optical synthetic aperture imaging system in a blind way. Numerical simulation and experiment results show that RestoreNet is an effective alternative with great restoration ability, stability and generalization in the image restoration of optical synthetic aperture imaging system. [ABSTRACT FROM AUTHOR]

• We present a multi-camera-based method for improving data capture speed in Fourier ptychographic microscopy. • A new reconstruction algorithm along with robust calibration methods are proposed for multi-camera Fourier ptychographic systems. • A proof-of-concept experiment is performed to validate the principle by imaging a resolution target and a plant root cross section, using 9 times fewer LED illuminations compared to a regular Fourier ptychographic setup. We present a novel microscopy concept, termed Multi-Aperture Fourier ptychographic microscopy (MA-FPM), to enable implementation of parallel detectors in microscopy to increase the space-bandwidth-time product. MA-FPM is a synthetic aperture technique: an array of objectives together with tilt-shift illumination are used to synthesize high-resolution, wide field-of-view images. Here, the phase is recovered using Fourier ptychography (FP) algorithms unlike conventional optical synthetic aperture techniques where holographic measurements are used. In this article we report a proof-of-concept experiment by translating a lens and a detector to positions according to the proposed design and demonstrate high-quality imaging performance despite using nine-fold fewer illumination angles compared to an equivalent FP setup. Calibration procedures and a reconstruction algorithm were developed to address the challenges of multiple imaging systems. [ABSTRACT FROM AUTHOR]

• F-DMAS is modified by introducing a weighting factor in the beamforming process. • The novel beamformers, F-D w MAS and F-D ew MAS, were evaluated on the 2R-SAFT. • F-D w MAS and F-D ew MAS yields better image quality compared to DAS and F-DMAS. • The above improvements are more prominent at greater depths. • The proposed approach shows potential, especially for high frequency ultrasound. In this paper, the development of modified beamforming methods, Filtered Delay Weight Multiply and Sum (F-D w MAS) and Filtered Delay Euclidian-Weighted Multiply and Sum (F-D ew MAS), are reported. These methods were investigated on a minimum-redundancy synthetic aperture technique, called as 2 element Receive Synthetic Aperture Focusing Technique (2R-SAFT), which uses one element on transmit and two consecutive elements on receive, for reducing hardware complexity without compromising much on the image quality. The performance of the developed F-D w MAS and F-D ew MAS methods were compared with Delay and Sum (DAS) and recently introduced F-DMAS beamforming methods. Notably, in the proposed methods, an additional aperture window function is designed and incorporated to the F-DMAS method. The different methods of F-D w MAS, F-D ew MAS, F-DMAS and DAS were compared in terms of the resulting image quality metrics, Lateral Resolution (LR), Axial Resolution (AR), Contrast Ratio (CR) and contrast-to-noise ratio (CNR), in simulation and experiments on tissue-mimicking phantoms. Experimental results show that (F-D w MAS) and {F-D ew MAS} resulted in improvements of AR by (46.32% and 23.51%), {43.56% and 17.78%}, LR by (47.81% and 30.27%), {44.26% and 26.14%} and CR by (45.68% and 17.15%), {42.16% and 9.87%} compared to those obtained using DAS and F-DMAS, respectively. However, CNR of F-D w MAS and F-D ew MAS was found to be 31.19% and 21.16% less compared to DAS, but 4.89% and 18.64% more than F-DMAS, respectively. Hence, it can be concluded that the image quality improved by both F-D w MAS and F-D ew MAS compared to DAS and F-DMAS. Also, between F-D w MAS and F-D ew MAS, the later has the advantage of ready applicability to different acquisition schemes and settings compared to the former also having an additional advantage of better CNR compared to both F-DMAS and F-D ew MAS. [ABSTRACT FROM AUTHOR]

We demonstrate the photonic-assisted high-resolution synthetic aperture radar imaging applying broadband photonic signal generation and a modified incoherent back projection (BP) imaging algorithm. The radar transmits linear frequency modulated (LFM) signals generated by period-one oscillation in an optically injected semiconductor laser. Since the signal bandwidth is greatly enlarged compared with traditional electric radars, a significantly improved imaging resolution can be achieved. Besides, we use a modified incoherent BP imaging algorithm with self-amplitude weighting and multiplicative tomography weighting, to further increase the imaging resolution and to suppress the undesired high-energy artifacts and background interferences. An experiment is carried out. Based on the established radar with a signal bandwidth as large as 12 GHz, high-resolution and clear images of different scenes are successfully constructed, through which the advantages of the proposed scheme over traditional BP imaging system can be soundly verified. The demonstrated scheme provides a good solution to enhance the performance of the incoherent BP imaging algorithm and simultaneously overcome the radar bandwidth limitation. It would find applications where high-resolution radar imaging is needed. [ABSTRACT FROM AUTHOR]