- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Pixel-Wise MTInSAR Estimator for Integration of Coherent Point Selection and Unwrapped Phase Vector Recovery
摘要： Coherent point (including persistent and distributed scatterers) selection and phase ambiguity treatment (or parameter estimation) are the key tasks involved in multitemporal InSAR (MTInSAR) algorithms, which are usually conducted separately with empirical thresholds. It is not rare to see that due to the discrepancies on threshold setting, even for the same MTInSAR technique with the same data sets, it will raise different (sometimes quite notable) results and affect the applicability of InSAR techniques. We propose here an integrated MTInSAR estimator that combines the coherent point selection and phase vector unwrapping into a single step. Essentially, the estimator aims to recover the unwrapped phase vector at coherent points. Therefore, it could serve as an alternative solution of spatial–temporal phase unwrapping problem. In the estimator, wrapped phase at all pixels in short baseline interferograms are taken as observations. Starting from the phase differences at arcs of a fully connected network of pixels, based on the residual analysis and spatial closure of phase triangularity, the estimator can detect and delete the arcs having unacceptable phase noise and phase ambiguities. By integrating the phase differences at the remained arcs, the unwrapped phase at coherent points in consecutive acquisition intervals can be obtained. Impressively, the estimator is immune to the bias raised by improper deformation model. The performance of the proposed estimator is evaluated via semisynthetic and real data tests. Considering that the phase enhancement algorithms (e.g., phase-linking and Extended Minimum Cost Flow-Small BAseline Subset) that can reconstruct high-quality wrapped phases are gaining popularity, the proposed estimator can also be implemented as a postprocessing module of these algorithms for retrieval of unwrapped phase vectors at coherent points.
关键词： phase unwrapping,phase recovery,InSAR (MT-InSAR),consistency,Ambiguity detection,coherent points detection
更新于2025-09-10 09:29:36
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[IEEE 2018 IEEE 3rd International Conference on Image, Vision and Computing (ICIVC) - Chongqing (2018.6.27-2018.6.29)] 2018 IEEE 3rd International Conference on Image, Vision and Computing (ICIVC) - Multiple Chinese Vehicle License Plate Localization in Complex Scenes
摘要： License plate localization is an essential part of automated vehicle license plate recognition (ALPR). This paper proposes a two-step approach of the vehicle license plate (LP) localization which includes a novel attempt for LP detection and a new method for LP skew correction. The proposed approach begins with detecting the LP region while classifying the LP type in the image using single shot multi-box detector (SSD) and then further precisely determining the LP corner points in detected region by fitting LP borderlines according to the character contours based on the multi-level thresholding binarization. The experiment evaluated the performance of the proposed method on 600 vehicle images (~800(cid:13)(cid:13)800) captured under realistic complex environment. The result shows that LPs in 579 images can be localized exactly (96.5% accuracy) and processing speed is up to 27 FPS on average.
关键词： single shot multi-box detection,license plate corner points determination,vehicle license plate localization
更新于2025-09-10 09:29:36
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Exceptional points in a time-periodic parity-time-symmetric Rabi model
摘要： We investigate the effect of a periodic modulation on parity-time symmetry in a non-Hermitian Rabi model with balanced gain or loss. It is shown that under the multiple-photon resonance conditions, this Rabi model supports exact Floquet solutions for certain special parameter conditions which allow us to find exact analytical results for the position of certain exceptional points (EPs). It is also found numerically that there exists a universal relation between the number of the EPs and the gain or loss strength.
关键词： non-Hermitian Rabi model,exceptional points,Floquet solutions,parity-time symmetry,periodic modulation
更新于2025-09-10 09:29:36
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Higher Order Exceptional Points in Discrete Photonics Platforms
摘要： The introduction of parity-time (PT) symmetry in optics and photonics has initiated intense activities exploring the exotic properties of these structures, eventually leading to the more general notion of non-Hermitian photonics. Efforts to understand the behavior of these systems have revealed a host of distinct features originating from the unusual character of their eigenspectra and eigenstates. These include for example, spontaneous symmetry breaking, bandgap merging, laser self-termination, unidirectional invisibility, and ultra-sensitivity to external perturbations. A central notion pertinent to all these effects is the concept of exceptional points (EPs). Also known as branch points, EPs are non-Hermitian spectral singularities that arise when two (or more) eigenvalues and their corresponding eigenstates become identical. While exceptional points of order two have been studied thoroughly at both the theoretical and experimental level, higher order EPs are attracting attention only recently. Here we discuss a systematic approach based on a recursive bosonic quantization scheme for generating discrete photonic networks that exhibit exceptional points of any arbitrary order. We also discuss the spectral properties and the extreme dynamics near these singularities as well as their physical implementation in various photonic platforms.
关键词： non-Hermitian photonics,parity-time symmetry,photonic networks,recursive bosonic quantization,exceptional points
更新于2025-09-10 09:29:36
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Construction of Non- P T $$\mathbb {PT}$$ -Symmetric Complex Potentials with All-Real Spectra
摘要： We review recent work on the generalization of PT symmetry. We show that, in addition to PT -symmetric complex potentials, there are also large classes of non-PT -symmetric complex potentials which also feature all-real spectra. In addition, some classes of these non-PT -symmetric potentials allow phase transitions which do or do not go through exceptional points. These non-PT -symmetric potentials are constructed by a variety of methods, such as the symmetry and supersymmetry methods and the soliton theory. A generalization of PT symmetry in multi-dimensions is also reviewed.
关键词： all-real spectra,exceptional points,soliton theory,symmetry methods,supersymmetry methods,non-PT -symmetric potentials,PT symmetry,phase transitions
更新于2025-09-10 09:29:36
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Non-Hermitian Effects Due to Asymmetric Backscattering of Light in Whispering-Gallery Microcavities
摘要： A whispering-gallery microcavity is an open optical system which supports well con?ned counterpropagating electromagnetic waves. Deforming the boundary of the cavity or perturbing it by other means, e.g. by placing small scatterers near the boundary, leads to coherent backscattering of these waves inside the cavity. In general, this backscattering is asymmetric, i.e. the strength of scattering from the clockwise to the counterclockwise propagation direction is different from the other way around. This asymmetry is intrinsically tied to the non-Hermiticity of the system including the nonorthogonality of mode pairs and the coalescence of modes at exceptional points. We review and present new results on asymmetric backscattering with emphasis on its non-Hermitian effects. Several types of perturbed whispering-gallery cavities are considered. Different applications, such as single-particle detection with enhanced sensitivity, are discussed.
关键词： whispering-gallery microcavities,chirality,copropagation,asymmetric backscattering,nonorthogonality,Non-Hermitian effects,exceptional points
更新于2025-09-10 09:29:36
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Accuracy of Unmanned Aerial Vehicle (UAV) and SfM Photogrammetry Survey as a Function of the Number and Location of Ground Control Points Used
摘要： The geometrical accuracy of georeferenced digital surface models (DTM) obtained from images captured by micro-UAVs and processed by using structure from motion (SfM) photogrammetry depends on several factors, including flight design, camera quality, camera calibration, SfM algorithms and georeferencing strategy. This paper focusses on the critical role of the number and location of ground control points (GCP) used during the georeferencing stage. A challenging case study involving an area of 1200+ ha, 100+ GCP and 2500+ photos was used. Three thousand, four hundred and sixty-five different combinations of control points were introduced in the bundle adjustment, whilst the accuracy of the model was evaluated using both control points and independent check points. The analysis demonstrates how much the accuracy improves as the number of GCP points increases, as well as the importance of an even distribution, how much the accuracy is overestimated when it is quantified only using control points rather than independent check points, and how the ground sample distance (GSD) of a project relates to the maximum accuracy that can be achieved.
关键词： Unmanned Aerial Vehicles (UAV),accuracy,structure from motion,ground control points
更新于2025-09-10 09:29:36
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The Evaluation of Static Deficiencies of Lower Limbs with the Use of Non-Contact Measurement
摘要： The purpose of this paper is to develop a procedure of the lower limbs volumetric modelling using the laser measurement arm and the evaluation of defects, which can cause disorders in the field of locomotion. The procedure is presented based on the analysis of two specimens: woman (age 22) and man (age 23), whose lower limbs are fully formed. The method includes the laser scanning and the lower limbs regularity evaluation based on the characteristic lines, which were identified during palpation examination of the skin and bones characteristic points or during the radiological examination. The valgus knee and the knee joint hyperextension were determined for the woman’s case and no deficiencies for the man’s case. Presented procedure has a screening application and can support the rehabilitation process. The advantage is that the developed method is noninvasive and the diagnostics can be performed while muscles are active in the natural standing position. The SL method was verified by the Laser Tracker system. On the group of 55 students with the average age of 10.4 years, the measurements were performed in order to define the influence of BMI on the correctness of the results, which were achieved while using the proposed method of the evaluation of the static deficiencies. No relevant influence of BMI on errors occurring in the determination of defects valgus and varus of the lower limbs.
关键词： Valgus,BMI,Characteristic points,Varus,3D modelling,Baseline,Laser scanning
更新于2025-09-10 09:29:36
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Theory of relaxation oscillations in exciton-polariton condensates
摘要： We provide an analytical and numerical description of relaxation oscillations in the nonresonantly pumped polariton condensate. Presented considerations are based on coupled rate equations that are derived from the open dissipative Gross-Pitaevskii model. The evolution of the condensate density can be explained qualitatively by studying the topology of the trajectory in phase space. We use a ?xed points analysis for the classi?cation of the different regimes of condensate dynamics, including fast stabilization, slow oscillations, and ultrashort pulse emission. We obtain an analytical condition for the occurrence of relaxation oscillations. Continuous and pulsed condensate excitations are considered and we demonstrate that, in the latter case, the existence of the second reservoir is necessary for the emergence of oscillations. We show that relaxation oscillations should be expected to occur in systems with relatively short polariton lifetimes.
关键词： phase space,nonresonantly pumped,relaxation oscillations,fixed points analysis,exciton-polariton condensates,Gross-Pitaevskii model
更新于2025-09-09 09:28:46
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Precision optical metrology with alkali-atom isoclinic points
摘要： Vapour-phase spectroscopy rarely involves transitions between well-isolated atomic states. Routinely, the spectra comprise overlapped Doppler/pressure-broadened resonances, which leads to a “pulling” of the spectral peaks from their true atomic resonance frequencies. This pulling gives the absorption resonances a temperature sensitivity, which limits their utility for precision spectroscopy when sub-Doppler techniques are not viable. Here, we discuss the use of alkali isoclinic points as a solution to this problem.
关键词： precision spectroscopy,alkali isoclinic points,vapor-phase spectroscopy,Doppler/pressure-broadened resonances
更新于2025-09-09 09:28:46