- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Properties of the Finite Airy beam propagating in the misaligned slab system with a rectangular aperture
摘要： In this letter, we deduce the approximate analytical formula for the finite Airy beam propagating in the misaligned slab system with a rectangular aperture by using the generalized Huygens-Fresnel integral equation, the light transfer matrix and expanding the hard-edged rectangular function into a finite sum of complex Gaussian function. The particular cases of this beam propagating in the apertured aligned slab system, unapertured misaligned slab system and unapertured aligned one are further illustrated through numerical examples as well. The effects of aperture size and misaligned factors on beam evolution in these slab structures are developed, which can provide a fast and effective method for investigating other kinds of pseudo non-diffracting laser beams through the rectangularly apertured misaligned slab system because most of the optical devices are slightly misaligned more or less in the practical application.
关键词： Finite Airy beam,Generalized Huygens-Fresnel integral equation,Misalignment,Rectangular aperture,Transfer matrix
更新于2025-09-10 09:29:36
-
One-bit compressive sensing with time-varying thresholds in synthetic aperture radar imaging
摘要： In this study, the authors introduce a new framework for 1-bit compressed synthetic aperture radar (SAR) imaging by using time-varying thresholding. They show how to recover sparse SAR images from noisy measurements which have been quantised to 1-bit with time-varying thresholds. In the conventional 1-bit compressive sensing (CS) SAR imaging methods, 1-bit quantisation is implemented by comparing the received signal to a zero threshold. This makes the information about the magnitude of the signal to be lost and exact signal recovery becomes impossible. One-bit quantisation with time-varying thresholds allows them to reconstruct the magnitude of the signal more accurately and an explicit unit-norm constraint is no longer required in the proposed optimisation formulation. Using the proposed approach, the authors formulate 1-bit CS SAR imaging reconstruction problem as an unconstrained optimisation problem where the objective function includes an ?2 data-fidelity term and a non-smooth regularisation function. In order to solve this unconstrained optimisation problem, they use variable splitting and the alternating direction method of multipliers based approach which is computationally efficient and easy to implement. The results from experiments with synthetic and real SAR images validate the effectiveness of the proposed method named as BCST-SAR (binary CS with time-varying thresholds in SAR imaging).
关键词： ADMM,time-varying thresholds,sparse signal recovery,1-bit compressive sensing,synthetic aperture radar
更新于2025-09-10 09:29:36
-
Three-Dimensional Terahertz Coded-Aperture Imaging Based on Geometric Measures
摘要： For synthetic aperture radars, it is dif?cult to achieve forward-looking and staring imaging with high resolution. Fortunately, terahertz coded-aperture imaging (TCAI), an advanced radar imaging technology, can solve this problem by producing various irradiation patterns with coded apertures. However, three-dimensional (3D) TCAI has two problems, including a heavy computational burden caused by a large-scale reference signal matrix, and poor resolving ability at low signal-to-noise ratios (SNRs). This paper proposes a 3D imaging method based on geometric measures (GMs), which can reduce the computational burden and achieve high-resolution imaging for low SNR targets. At extremely low SNRs, it is dif?cult to detect the range cells containing scattering information with an ordinary range pro?le. However, this dif?culty can be overcome through GMs, which can enhance the useful signal and restrain the noise. By extracting useful data from the range pro?le, target information in different imaging cells can be simultaneously reconstructed. Thus, the computational complexity is distinctly reduced when the 3D image is obtained by combining reconstructed 2D imaging results. Based on the conventional TCAI (C-TCAI) model, we deduce and build a GM-based TCAI (GM-TCAI) model. Compared with C-TCAI, the experimental results demonstrate that GM-TCAI achieves a more impressive performance with regards to imaging ability and ef?ciency. Furthermore, GM-TCAI can be widely applied in close-range imaging ?elds, for instance, medical diagnosis, nondestructive detection, security screening, etc.
关键词： three-dimensional (3D),geometric measures (GMs),pulse compression,coded-aperture imaging
更新于2025-09-10 09:29:36
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Coherence Change Detection For Sentinel-1 Sar: Methods And Applications
摘要： We propose a full Space and Time Coherent Change Detection (ST-CCD) that takes advantage of Sentinel-1 (S1) short interferometric revisit to enhance sensitivity in detecting changes at a fine space resolution. It extends the Generalized Likelihood Ratio Test (GLRT) used for change detection by single baseline images, to the multi-pass, multi-polarimetric stacks of S1 data. Applications are shown for damage mapping after hazards and for agriculture. A preliminary validation is performed by processing data referred to central Italy earthquake in 2016.
关键词： interferometry,damage mapping,Synthetic aperture radar,multidimensional signal detection
更新于2025-09-10 09:29:36
-
First measurements of the vertical beam size with an X-ray beam size monitor in SuperKEKB rings
摘要： This paper reports first measurements of the vertical beam size using an X-Ray Beam Size Monitor (XRM) for each of the SuperKEKB rings (Low Energy Ring, LER, and High Energy Ring, HER) during Phase 1 and 2 commissioning of SuperKEKB. The XRM device is dedicated to measuring the e?/e+ vertical beam size using X-ray synchrotron radiation, and will eventually have the capability for single-shot (single bunch, single turn) measurements. The preparation of a deep Si detector and high-speed readout electronics for single-shot measurements is underway. In the meantime for Phase 1 and 2, we used a scintillator screen and CCD camera for multi-bunch measurements. The XRM has been installed in each ring and images X-rays from a bending magnet that pass through optical elements (a single pinhole and coded apertures). Several studies (geometrical scale factors, emittance control knob, and beam lifetime study) were carried out during the commissioning. In Phase 1 (February-June 2016), the measured vertical emittances εy are ～10 pm for LER (consistent with the optical estimation) and ～35 pm for HER (3.5× greater than the optical estimation). Analysis of the beam size and lifetime measurements suggests unexpectedly large point spread functions (PSF), particularly in the HER. The spatial resolution of the imaging system (defect of focus, diffraction, and spherical aberration) and scattering in the beamline (EGS5 simulation) contribute ～6 μm of PSF, which does not adequately account for the observed PSF. The Phase 2 commissioning commenced in May-July 2018, with thinner Be filters, new optical elements, scintillator, and CCD camera with the purpose to reduce the PSF in HER. The Phase 2 study results suggest the PSF σs ～6.6 μm in HER (corresponding to the spatial resolution of the imaging system and scattering in the beamline), which is ～5× smaller than in Phase 1. The overall performances of XRMs in LER and HER are accurate. The XRM in LER will be able to measure the design beam size at the zero current (14 μm). For the HER, the PSF that we observed during the Phase 2 indicates that the minimum measured beam size corresponds to the emittance at the design current (12.9 pm) and the XRM will be able to measure the design beam size at the zero current (7 μm).
关键词： SuperKEKB,synchrotron radiation,vertical beam size,X-ray beam size monitor,coded aperture,pinhole
更新于2025-09-10 09:29:36
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Superpixel Segmentation with Boundary Constraints for Polarimetric SAR Images
摘要： Superpixel segmentation has been commonly used in various image processing tasks such as object detection and image classification. In this paper, we propose a novel superpixel segmentation method based on a new distance function and superpixel seed updating strategy for polarimetric synthetic aperture radar (PolSAR) images. We initialize superpixel seeds with an expected number of superpixels. Then, we iteratively cluster the pixels based on the distance function and update the superpixel seeds based on the updating str-ategy. When the termination condition is reaches, we stop the iteration and obtain the superpixels. The experimental results based on RADARSAT-2 data demonstrate that our method is effective and achieves a better tradeoff between boundary adherence and compactness.
关键词： Polarimetric synthetic aperture radar (PolSAR),image segmentation,superpixel
更新于2025-09-10 09:29:36
-
Beamforming Optimization for Time-Modulated Circular-Aperture Grid Array with DE Algorithm
摘要： This paper put forward a method of numerical optimization for the circular-aperture time-modulated grid array. The amplitude weight and time modulation pulse width are optimized based on differential evolution algorithm to get the needed array pattern. Adopting the weighting mode of conventional rectangular array, the equivalent weighting of circular-aperture time-modulated array is decomposed into two independent components respectively in horizontal and vertical direction, so to shorten the length of optimization vector from M×N order to M+N order. Besides, the circular-aperture time-modulated array is symmetrically excited in horizontal and vertical direction. The numerical experiments show that differential evolution algorithm can realize sidelobe level of -35dB and nulling level of -60dB in the patterns of the center frequency and one chosen sideband, and the unexploited sidebands are also suppressed with their peak level lower than -35dB. Meanwhile the dynamic range of the amplitude weighting and time modulation pulse width can be limited in 10dB. The overall efficiency of the time-modulated array is 0.28.
关键词： Beamforming optimization,differential evolution algorithm,circular-aperture grid array,time modulation
更新于2025-09-10 09:29:36
-
Ship Detection From PolSAR Imagery Using the Complete Polarimetric Covariance Difference Matrix
摘要： In this paper, we proposed a complete polarimetric covariance difference matrix [C P]-based algorithm for ship detection in polarimetric synthetic aperture radar (PolSAR) imagery. To calculate [C P], we first developed a scheme to reflect the polarimetric scattering differences between ship pixel (SP) and its neighboring pixels (ISPs) and, then, dividedly accumulated the amplitude and phase differences between SP and ISPs. Compared to the polarimetric covariance difference matrix [ P] developed in our earlier work, [C P] effectively overcomes the drawback of the lack of the phase information in [ P]. To demonstrate the effectiveness of the proposed algorithm, we applied the [C P]-based ship detection algorithm to four PolSAR data sets, including one UAVSAR L-band data set with 21 ships, two AIRSAR L-band data sets with 11 and 22 ships, respectively, and one Radarsat-2 C-band data set with 8 ships. Experimental results show that: 1) the proposed algorithm can effectively detect ships with high target-to-clutter ratio (TCR) values and 2) [C P] has a better performance than the traditional polarimetric covariance matrix [C] and [ P] on ship detection. To be more specific, the average TCR value of the proposed algorithm (23.86 dB) is 6.07 and 7.47 dB higher than PNFC (i.e., the geometrical perturbation-polarimetric notch filter) and RSC (i.e., the reflection symmetry method), respectively.
关键词： reflection symmetry (RS),target-to-clutter ratio (TCR),Complete polarimetric covariance difference matrix [C P],scattering differences,ship detection,polarimetric synthetic aperture radar (PolSAR) imagery,polarimetric notch filter (PNF)
更新于2025-09-10 09:29:36
-
The Polarimetric L-Band Imaging Synthetic Aperture Radar (PLIS): Description, Calibration, and Cross-Validation
摘要： The polarimetric L-band imaging synthetic aperture radar (PLIS) is a high spatial resolution (better than 6 m) airborne synthetic aperture radar system that has been dedicated to scientific research into civilian applications since 2010. The weight of PLIS is ～38 kg, allowing it to be installed aboard small low-cost aircraft, with two antennas used to measure the full backscatter matrix for a swath between 15° and 50° on each side of the flight direction. Calibration based on a total of 96 calibration points and a homogeneous forest during the two recent soil moisture active passive experiments (SMAPEx-4 and 5) showed an overall radiometric accuracy of 0.58 dB (root-mean-square error) over trihedral passive radar calibrators. Independent evaluation based on polarimetric active radar calibrators showed an amplitude imbalance of 0.17 dB with a standard deviation of 0.15 dB and a phase imbalance of 3.87° with a standard deviation of 2.86°. Two calibrated phased-array L-Band synthetic aperture radar-2 (PALSAR-2) images with different observation modes (ScanSAR and Stripmap) were compared with the calibrated PLIS images. The agreement between PALSAR-2 Stripmap and PLIS had a root mean square difference of 1.27 dB and a correlation coefficient of 0.87. Further comparisons over different landcover types confirmed that homogeneous forest and grassland areas constitute optimal targets for cross-validation and/or calibration.
关键词： Calibration and validation,phased-array L-Band synthetic aperture radar-2 (PALSAR-2),cross-calibration,synthetic aperture radar (SAR),polarimetric L-band imaging SAR (PLIS)
更新于2025-09-09 09:28:46
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Potential of the Reverse Synthesis Method for the High-Quality SAR Image Synthesis
摘要： A potential of a new Reverse synthesis method proposed at IGARSS 2017 for the high-quality Synthetic Aperture Radar (SAR) image synthesis is presented. Images produced by the method are compared with the best existing approaches for the speckle noise reduction. Further capabilities for the image quality improvement like side lobe, range and azimuth reduction, contrast improvement, autofocusing and target detectability improvement are considered. The novel approach allows both: to produce high quality and high-resolution images from existing SAR raw data and to create new high-quality systems with reduced demands to the on-board equipment.
关键词： SAR,speckle noise,image synthesis,high resolution,synthetic aperture radar,synthetic aperture imaging,image quality
更新于2025-09-09 09:28:46