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Cirrus clouds often contain numerous hollow ice crystals, which are distinct in scattering properties from solid ice crystals, and will be challenging to microphysical retrieval and radiative forcing assessment. Currently, hollow ice crystals have not been observed by remote sensing methods, and the estimation of their hollowness is a complex task. To address this issue, the Mixed Modal Hollow Columns (MMHC) model for hollow ice crystals is introduced, and its backscattering properties are computed using the physical optics approximation method. Through comparison with spaceborne lidar observations, we identify a specific type of cirrus associated with the MMHC model for the first time. The visible optical depth of this cirrus is less than or equal to 0.1, and the temperature is between −60 and −40°C. The MMHC characteristic cirrus clouds are prevalent in middle and high latitudes but less comm+on in low latitudes. They exhibit distinct patterns in terms of sea and land distribution as well as seasonal variation. Plain Language Summary: Cirrus clouds typically form at altitudes exceeding 6 km and consist of non‐spherical ice crystals, each with unique optical properties affecting the earth's radiation balance through scattering and absorption. Notably, these crystals include hollow formations, which are distinct in scattering properties from their solid counterparts. The coexistence of hollow and solid ice crystals presents challenges in accurately inverting ice crystal morphology in remote sensing and evaluating radiation properties in climate models. To address these complexities, we propose a MMHC model. Through analysis of spaceborne lidar observational data, we identify characteristic cirrus clouds associated with such type of ice crystals and study the global distribution and seasonal distribution of this kind of cirrus clouds. Key Points: A Mixed Modal Hollow Columns model is formulated to characterize the presence of hollow ice crystals in cirrus cloudsFor the first time, hollow characteristic cirrus clouds are observed using spaceborne lidarHollow characteristic cirrus clouds exhibit distinct global and seasonal distribution variations [ABSTRACT FROM AUTHOR]

Single-solution-based optimization algorithms are computationally cheap yet powerful methods that can be used on various optimization tasks at minimal processing expenses. However, there is a considerable shortage of research in this domain, resulting in only a handful of proposed algorithms over the last four decades. This study proposes the Prism Refraction Search (PRS), a novel, simple yet efficient, single-solution-based metaheuristic algorithm for single-objective real-parameter optimization. PRS is a physics-inspired algorithm modeled on a well-known optimization paradigm in ray optics arising from the refraction of light through a triangular prism. The key novelty lies in its scientifically sound background that is supported by the well-established laws of physical optics. The proposed algorithm is evaluated on several numerical objectives, including 23 classical benchmark functions, the CEC-2017 test suite, and five standard real-world engineering design problems. Further, the results are analyzed using standard statistical tests to prove their significance. Extensive experiments and comparisons with state-of-the-art metaheuristic algorithms in the literature justify the robustness and competitive performance of the PRS algorithm as a lightweight and efficient optimization strategy. [ABSTRACT FROM AUTHOR]

Synchrotron light sources can provide the required spatial coherence, stability and control to support the development of advanced lithography at the extreme ultraviolet and soft X-ray wavelengths that are relevant to current and future fabricating technologies. Here an evaluation of the optical performance of the soft X-ray (SXR) beamline of the Australian Synchrotron (AS) and its suitability for developing interference lithography using radiation in the 91.8 eV (13.5 nm) to 300 eV (4.13 nm) range are presented. A comprehensive physical optics model of the APPLE-II undulator source and SXR beamline was constructed to simulate the properties of the illumination at the proposed location of a photomask, as a function of photon energy, collimation and monochromator parameters. The model is validated using a combination of experimental measurements of the photon intensity distribution of the undulator harmonics. It is shown that the undulator harmonics intensity ratio can be accurately measured using an imaging detector and controlled using beamline optics. Finally, the photomask geometric constraints and achievable performance for the limiting case of fully spatially coherent illumination are evaluated. [ABSTRACT FROM AUTHOR]

For the application of vortex electromagnetic (EM) beams in practical detection scenes, the scattering characteristics of electrically large arbitrarily shaped targets illuminated by an off-axis Laguerre–Gaussian (LG) vortex beam are investigated and compared to the on-axis incidence case. The vector potential method is used to extract the electric and magnetic field components of the LG beam in different polarization states. The physical optics algorithm is adopted to calculate the scattering fields of four typical targets with the shape of a sphere, NASA almond, blunt cone, and blade model. The results revealed that as the beam center offset and the topological charge of the incident vortex beam increase, the scattering field distorts, and the obvious orbital angular momentum (OAM) spectrum mixing occurs. In addition, OAM spectrum aliasing occurs for asymmetric targets, even at on-axis incidence. These results elucidate the mechanism of vortex EM scattering and provide a reference for applying vortex beams for target detection and recognition. [ABSTRACT FROM AUTHOR]

This paper illustrates an interferometric inverse synthetic aperture radar based on three‐dimensional imaging and rotational velocity estimation from a multistatic setup with three ground‐based radars with non‐orthogonal baselines. The radar backscattering along the orbit is simulated based on physical optics approximation. The paper illustrates a novel shape‐dependent and rotation‐invariant feature called normalised eigenvalues for classification. A database of interferometric point clouds is generated using radar back scattering at different aspect angles and classified using various classification algorithms. The classification accuracy at varying SNR levels was evaluated using Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

In this study, we obtained the intensity and orbital angular momentum (OAM) spectral distribution of the scattering fields of vortex electromagnetic beams illuminating electrically large targets composed of different materials. We used the angular spectral decomposition method to decompose a vortex beam into plane waves in the spectral domain at different elevations and azimuths. We combined this method with the physical optics algorithm to calculate the scattering field distribution. The OAM spectra of the scattering field along different observation radii were analyzed using the spiral spectrum expansion method. The numerical results indicate that for beams with different parameters (such as polarization, topological charge, half-cone angle, and frequency) and targets with different characteristics (such as composition), the scattering field intensity distribution and OAM spectral characteristics varied considerably. When the beam parameters change, the results of scattering from different materials show similar changing trends. Compared with beams scattered by uncoated metal and dielectric targets, the scattering field of the coating target can better maintain the shape and OAM mode of beams from the incident field. The scattering characteristics of metal targets were the most sensitive to beam-parameter changes. The relationship between the beam parameters, target parameters, the scattering field intensity, and the OAM spectra of the scattering field was constructed, confirming that the spiral spectrum of the scattering field carries the target information. These findings can be used in remote sensing engineering to supplement existing radar imaging, laying the foundation for further identification of beam or target parameters. [ABSTRACT FROM AUTHOR]

The detection of weak time-dependent alternating signals in a strongly noisy background is an important problem in physics and a critical task in metrology. Quantum lock-in amplifier can extract alternating signals within extreme noises by using suitable quantum resources, which has been widely used for magnetic field sensing, vector light shift detection, and force detection. In particular, entanglement-enhanced quantum lock-in amplifier can be realized via many-body quantum interferometry. The many-body lock-in measurement provides a feasible way to achieve high-precision detection of alternating signals, even in noisy environments. In this article, we review general protocol, experiment progresses and potential applications of quantum lock-in measurements. [ABSTRACT FROM AUTHOR]

Correlations between stochastic electromagnetic beams' intensity variations which are produced by sources with anisotropic crossspectral density matrices are explored. Recently introduced spectral degree of cross-polarization, spectral degree of coherence, and the intensity fluctuations of electromagnetic sources are analyzed upon propagation by considering the source as an anisotropic beam. An analytical formula is given for the cross-spectral density matrix of an anisotropic electromagnetic Gaussian Schell beam moving across free space and extended to longitudinal and transverse directions. The analysis shows that the cross-polarization of two beams having same source parameters might increase or decrease on propagation depending on the anisotropy ratio α. Numerical results are presented to show that the beam anisotropy might be one of the convenient methods for modeling partially coherent sources. [ABSTRACT FROM AUTHOR]

The capability to design, manufacture and test Hypersonic Glide Vehicles (HGVs) has been demonstrated by a number of nations, and they are increasingly forming part of military inventories, potentially offering capabilities highly unique to this technology. This article reports the simulated Monostatic Radar Cross Section of a generic HGV in five frequency ranges, HF, VHF, UHF, L, and S‐bands associated with different radar types. Full spherical datasets of complex co‐ and cross‐polar data are synthesised so that backscatter resulting from illumination by r.f./microwave energy of linear or circular polarisation can subsequently be computed from the raw dataset. Circular polarisation is commonly employed by ground‐based Ballistic Missile Early Warning Systems and Space Object Surveillance and Identification radars to avoid polarisation mis‐match losses resulting from ionospheric Faraday rotation effects. The data was generated using Ansys' Finite Element Solver at 10, 150 and 430 MHz, with the Geometric Optics/Physical Optics based SBR+ solver employed for 1.3 and 3 GHz data. All data was produced at below the Nyquist sampling interval relevant to the target's electrical size. These datasets were then imported into a Matlab routine which extracted data over limited angular ranges associated with the likely radar line‐of‐sight in particular scenarios, typically having a standard deviation of ±10° about the direction of flight, applying either a Gaussian or Uniform sampling distribution as part of a Monte Carlo analysis. These extracted data were then used to form histograms giving the probability of sampling particular RCS values. Probability density functions and cumulative distribution functions were then fitted, to aid in the representation of statistical target fluctuations for each band and angular sampling range. The HGV exists in either the 'Rayleigh', 'resonance' or 'optical' scattering regimes, depending on its relative electrical size. The results suggest that for this target shape at HF and VHF cases a simple Swerling 0 (fluctuation invariant) approximation is adequate in most instances, whilst a Gamma distribution may be applied for UHF band cases. At L and S‐band a Beta distribution was found to provide a good fit to the available data. [ABSTRACT FROM AUTHOR]

Off-axis parabolic mirrors (OAPMs) are widely used in the THz and mm-wave communities for spectroscopy and imaging applications, as a result of their broadband, low-loss operation and high numerical apertures. However, the aspherical shape of an OAPM creates significant geometric aberrations: these make achieving diffraction-limited performance a challenge, and lower the peak electric field strength in the focal plane. Here, we quantify the impact of geometric aberrations on the performance of the most widely used spectrometer designs, by using ray tracing and physical optics calculations to investigate whether diffraction-limited performance can be achieved in both the sample and the detector plane. We identify simple rules, based on marginal ray propagation, that allow spectrometers to be designed that are more robust to misalignment errors, and which have minimal aberrations for THz beams. For a given source, this allows the design of optical paths that give the smallest THz beam focal spot, with the highest THz electric field strength possible. This is desirable for improved THz imaging, for better signal-to-noise ratios in linear THz spectroscopy and optical-pump THz-probe spectroscopy, and to achieve higher electric field strengths in non-linear THz spectroscopy. [ABSTRACT FROM AUTHOR]

The knife‐edge diffraction model (KED) and the uniform geometrical theory of diffraction (UTD) have been widely used to predict the shadowing effect at millimetre‐wave (mmWave) bands. This letter proposes a mathematical derivation to rigorously prove that, for an absorbing screen, UTD applying the narrow‐angle Fresnel approximation is equivalent to KED. The simulation scenarios are designed to validate the proposal by comparing KED with UTD in the narrow‐angle (less than 20°) and wide‐angle (over 20°) regions at mmWave bands (20100 GHz). Simulated results agree with the proposal that KED is identical to UTD with a low error of less than 0.1 dB in the narrow‐angle region, while they have a difference with an error of over 1 dB in the wide‐angle region. In addition, the average computational time is measured and results in both UTD and KED taking approximately 8.0 ms for one test. From the proposal, it can be theoretically explained the differences and similarities between KED and UTD for an absorbing screen. [ABSTRACT FROM AUTHOR]

Reaction conditions: o -formylbenzoic acid (1a) (0.2 mmol), benzylamine (2a) (0.2 mmol), acetophenone (3a) (0.6 mmol), H 2 O (1 mL), 70 °C. When the molar ratio of I o i -formylbenzoic acid/benzylamine/acetophenone was 1:1:3, the highest yield of 71% was obtained. Reaction conditions: o -formylbenzoic acid (1a) (0.2 mmol), benzylamine (2a) (0.2 mmol), acetophenone (3a) (0.6 mmol), H 2 O (1 mL), 12 h. Keywords: isoindolin-1-one; water; catalyst-free; three-component reaction; o -formylbenzoic acid EN isoindolin-1-one water catalyst-free three-component reaction o -formylbenzoic acid 3172 3178 7 09/11/23 20231004 NES 231004 Graph Nitrogen-containing heterocycles are an important class of compounds, and form the basic skeletons of many drugs, natural products, and functional materials. [Extracted from the article]

In this review work, we give a review of recent works of high-frequency electromagnetic (EM) wave scattering in complex media and structures. The EM wave scattering from electrically large scatterers remains an important and challenging problem. We introduce the quadratic patches to discretize the electrically large scatterers and present the fast physical optics (FPO) method to solve the PO radiation integral. The computational workload and accuracies of the physical optics (PO) scattered fields from the quadratic patches are error-controllable and frequency-independent, respectively. To remedy the limitations of the accuracies of the PO scattered fields in the lit region of the electrically large scatterers, we consider the Fock current from the convex scatterers to cover the contributions of creeping wave fields in the shadow region. For the coated material from the perfectly conducting structure, we propose the multi-level technique together with the PO method to calculate the scattered field in an efficient way. In the process of mesh discretization for electrically large scatterers, we adopt the quadratic patches and further extend them to adaptive patches. For the multi-scale scatterers, we use the hybrid method of moment and FPO (MoM-FPO) method to calculate the scattered field from the multi-scale scatterers. [ABSTRACT FROM AUTHOR]

The "Synchrotron Radiation Workshop" (SRW) code is a computer program developed by the European Synchrotron Radiation Facility in 1997. It is used for simulating X-ray beamlines and coherence-exploiting experiments at synchrotron light sources. The code allows for the simulation of partially coherent wavefront propagation and the calculation of intensity distributions and coherence lengths. It has been used for electron beam diagnostics and offers brighter and more coherent X-ray beams for scientific experiments. The code is continuously developed and has interfaces with various software platforms. The article provides examples of simulations and mentions ongoing development and support from different organizations and research facilities. [Extracted from the article]

The rough structure may affect the flow field and electromagnetic (EM) scattering characteristics of a hypersonic vehicle. In this study, the EM scattering characteristics of the hypersonic vehicle RAM C-II with a microrough surface were investigated in the millimeter wave band. We first simulated the flow field of a smooth RAM C-II vehicle and calculated the radar cross section (RCS) in the wideband using the physical optics method. The calculation results show that many factors contribute to the variation in the RCS; however, it is occasionally difficult to predict. We then used a one-dimensional Gaussian random rough surface to generate a RAM C-II with a microrough surface through a point-coordinate transformation and simulated its flow field. The electron density flow field of the rough surfaced aircraft fluctuates greatly on the wall. Finally, we calculated the RCS of RAM C-II with different values of roughness in the millimeter wave band. The change of surface structure can be reflected in millimeter waves, and the RCS is determined by both plasma and rough structure. [ABSTRACT FROM AUTHOR]

The Shack–Hartmann wavefront sensor (SHWS) is a common option to characterize optical fields, due to its noninterference, high accuracy, and high-speed advantages. However, the current methods for evaluating measurement accuracy can only work for predefined standard wavefronts and cannot provide the error estimate for an arbitrary wavefront. Here, we propose an SHWS uncertainty evaluation approach for specific wavefronts based on the physical optics propagation. Our approach constructs a comprehensive SHWS model that incorporates twelve error sources. We analyzed the influence of different error sources on the measurement accuracy under the diffraction effect and reported that our model could achieve an accuracy of λ/559 under the ideal condition. In the experiment, we measured three different wavefronts and confined their uncertainty down to λ/65, λ/260, and λ/40, respectively. Our work may offer an effective solution for evaluating measurement errors in the high-accuracy wavefront measurement and provide a reliable, unbiased evaluation criterion. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to study the radar cross-section (RCS) of an intermeshing rotor with blade pitch. Design/methodology/approach: The variation of rotor blade pitch is designed into three modes: fixed mode, linear mode and smooth mode. The dynamic process of two crossed rotors is simulated, where the instantaneous RCS is calculated by physical optics and physical theory of diffraction. Findings: Increasing the pitch angle in the fixed mode can reduce the average RCS of rotor at the given head azimuth. The RCS curve of helicopter in linear mode and smooth mode will have a large peak in the side direction at the given moment. Although the blade pitch in smooth mode is generally larger than that in fixed mode, the smooth mode is conducive to reducing the peak and mean value of helicopter RCS at the given heading azimuth. Originality/value: The calculation method for analyzing RCS of intermeshing rotor with variable blade pitch is established. [ABSTRACT FROM AUTHOR]

Phase-space transforms describe spatial and angular information about light sources where one example is the Wigner functions in wave optics. Stokes parameters, on the other hand, supply information about the polarization of light beams. The generalized phase space Stokes parameters of 2D stochastic electromagnetic beams are already developed. In this article, the application of anisotropic light sources in generalized phase space Stokes parameters is theoretically investigated and numerically analyzed. There are several different ways of studying electromagnetic light beams depending on the spatial domain. But, most measure of the polarization of random light fields is carried out within the Stokes parameters context. In this account we study the electromagnetism, Stokes parameters, phase space, and the anisotropy properties of random light beams at once. We find here that when an anisotropy introduced in phase space then the cross terms of the Wigner matrix depart from the diagonal terms, which is not the same in configuration space. As a result, anisotropy has a different effect in Phase space, i.e. an anisotropic source introduces a phase and a variance change only in the cross terms of Wigner matrix. This is due to the use of anisotropy in the shifted kernel of Wigner transform. [ABSTRACT FROM AUTHOR]

LiteBIRD is a future satellite mission designed to observe the polarization of the cosmic microwave background radiation in order to probe the inflationary universe. LiteBIRD is set to observe the sky using three telescopes with transition-edge sensor bolometers. In this work we estimated the LiteBIRD instrumental sensitivity using its current design. We estimated the detector noise due to the optical loadings using physical optics and ray-tracing simulations. The noise terms associated with thermal carrier and readout noise were modeled in the detector noise calculation. We calculated the observational sensitivities over fifteen bands designed for the LiteBIRD telescopes using assumed observation time efficiency. [ABSTRACT FROM AUTHOR]

This paper presents the light-scattering matrices of atmospheric-aggregated hexagonal ice particles that appear in cirrus clouds. The aggregates consist of the same particles with different spatial orientations and numbers of these particles. Two types of particle shapes were studied: (1) hexagonal columns; (2) hexagonal plates. For both shapes, we studied compact and non-compact cases of particle arrangement in aggregates. As a result, four sets of aggregates were made: (1) compact columns; (2) non-compact columns; (3) compact plates; and (4) non-compact plates. Each set consists of eight aggregates with a different number of particles from two to nine. For practical reasons, the bullet-rosette and the aggregate of hexagonal columns with different sizes were also calculated. The light scattering matrices were calculated for the case of arbitrary spatial orientation within the geometrical optics approximation for sets of compact and non-compact aggregates and within the physical optics approximation for two additional aggregates. It was found that the light-scattering matrix elements for aggregates depend on the arrangement of particles they consist of. [ABSTRACT FROM AUTHOR]

Canonical objects with known radar cross section (RCS), for example, the trihedral corner reflector (TCR), play a crucial role in the calibration of automotive radar sensors. Moreover, these canonical objects are also used in the validation of simulated RCS obtained using asymptotic methods, such as hybrid geometric optics (GO) and the physical optics (PO) based methods. However, accurate RCS prediction with asymptotic methods is highly dependent on the individual scattering mechanisms considered in a simulation, for example reflection and diffraction from the TCR surfaces and edges, respectively. Reliable measurements are therefore required to evaluate if a particular interaction mechanism can be neglected to reduce computation complexity without adversely affecting the accuracy of the predicted RCS. In this letter, the monostatic scattering characteristics of three metallic TCRs are investigated with varying geometrical sizes in the E‐band, that is, from 60 GHz to 90 GHz. The ultra‐wideband (UWB) measurements, which offer a high delay resolution, can enable the identification of the individual scattering mechanisms. Diffraction from the TCR edges is experimentally demonstrated to contribute to a non‐negligible scattered power in this frequency band. [ABSTRACT FROM AUTHOR]

In this study physical optics (PO) surface current is obtained by using the Malyughinetz solution to get the scattered field expression for a truncated cylindrical conductive cap satisfying the related boundary conditions given throughout this paper. This is done by using the inverse edge point method for the transformation from the Malyughinetz solution for the wave diffraction by a half plane to the wave diffraction by a truncated conductive cylinder. This transformation method can be used to examine the diffraction and scattering phenomena for curved surfaces having discontinuities as dealt with in this work. Total scattered field comprising the incident and scattered fields is plotted with respect to the observation angle for some parameters of the problem. The obtained results are examined numerically for the same parameters. [ABSTRACT FROM AUTHOR]

Single-pass soil moisture retrieval has been a key objective of Global Navigation Satellite System-Reflectometry (GNSS-R) for the last decade. Achieving this goal will allow small satellites with GNSS-R payloads to perform such retrievals at high temporal resolutions. Properly modeling the soil surface roughness is key to providing high-quality soil moisture estimations. In the present work, the Physical Optics and Geometric Optics models of the Kirchhoff Approximation are implemented to the coherent and incoherent components of the reflectometry measurements collected by the SMAP radar receiver (SMAP-Reflectometry or SMAP-R). Two surface roughness products are retrieved and compared for a single-polarization approach, critical for single-polarization GNSS-R instruments that target soil moisture retrievals. Then, a polarization decoupling model is implemented for a dual-polarization retrieval approach, where the ratio between two orthogonal polarizations is evaluated to estimate soil moisture. Differences between linear and circular polarization ratios are evaluated using this decoupling parameter, and the theoretical soil moisture error with varying decoupling parameters is analyzed. Our results show a 1-sigma soil moisture error of 0.08 cm3/cm3 for the dual-polarization case for a fixed polarization decoupling value used for the whole Earth, and a 2-sigma error of 0.08 cm3/cm3 when the measured reflectivity and the VOD are used to estimate the polarization decoupling parameter. [ABSTRACT FROM AUTHOR]

This study estimated raindrop size distribution (DSD) and rainfall intensity with an infrared surveillance camera in dark conditions. Accordingly, rain streaks were extracted using a k -nearest-neighbor (KNN)-based algorithm. The rainfall intensity was estimated using DSD based on a physical optics analysis. The estimated DSD was verified using a disdrometer for the two rainfall events. The results are summarized as follows. First, a KNN-based algorithm can accurately recognize rain streaks from complex backgrounds captured by the camera. Second, the number concentration of raindrops obtained through closed-circuit television (CCTV) images had values between 100 and 1000 mm -1 m -3 , and the root mean square error (RMSE) for the number concentration by CCTV and PARticle SIze and VELocity (PARSIVEL) was 72.3 and 131.6 mm -1 m -3 in the 0.5 to 1.5 mm section. Third, the maximum raindrop diameter and the number concentration of 1 mm or less produced similar results during the period with a high ratio of diameters of 3 mm or less. Finally, after comparing with the 15 min cumulative PARSIVEL rain rate, the mean absolute percent error (MAPE) was 49 % and 23 %, respectively. In addition, the differences according to rain rate are that the MAPE was 36 % at a rain rate of less than 2 mm h -1 and 80 % at a rate above 2 mm h -1. Also, when the rain rate was greater than 5 mm h -1 , MAPE was 33 %. We confirmed the possibility of estimating an image-based DSD and rain rate obtained based on low-cost equipment during dark conditions. [ABSTRACT FROM AUTHOR]

HERAS is a tool developed in Matlab for the analysis of reflector antennas using physical optics (PO) theory. Its graphical user interface (GUI) and source code are freely available for educational and research purposes. It has the necessity of being a flexible tool to provide adaptability to system engineering requirements and can also be of interest to antenna engineers working on the design of reflector antennas. Due to the increasing demand of broadband services, satellite communications systems are becoming highly complex in order to meet connectivity requirements. To fully exploit the benefits of these systems, multidimensional optimisations are crucial, which call for an efficient estimation of the coverage characteristics. Reflector-based solutions are one of the preferred architectures for very high-throughput satellite (VHTS) systems. A detailed description of HERAS is presented in this paper which has been validated with available commercial software packages. In addition, some examples are described in which the tool has been used for the efficient estimation of VHTS systems performance. [ABSTRACT FROM AUTHOR]

Polarimetric decomposition is an effective way to analyze the scattering mechanism of targets in polarimetric synthetic aperture radar (PolSAR) images. However, the analysis of urban areas is frequently a challenge. Most decomposition methods use a rotated dihedral derived via rotation matrix to model the double-bounce scattering mechanism of buildings. However, according to electromagnetic theory, the existing dihedral model is not accurate, especially when the orientation angle of the dihedral is large. Therefore, the double-bounce scattering contribution in urban areas with large orientation angles will be difficult to extract. To address this problem, based on physical optics (PO) and geometric optics (GO), the interaction process of electromagnetic waves and the rotational dihedral is analyzed, and then a modified rotational dihedral model (MRDM) is proposed for the accurate representation of the rotational double-bounce scattering mechanism. Accordingly, MRDM is introduced to a five-component decomposition method (MRDM-5SD) to analyze the scattering components in an urban area. The validity of MRDM-5SD is demonstrated using several data sets. The experimental results show that the power contributions of double-bounce scattering in urban areas with large orientation angles increase by using MRDM-5SD. Therefore, MRDM can provide support for feature extraction and target detection in urban areas. [ABSTRACT FROM AUTHOR]

Optics means a general area of physics that covers a broad range of topics relevant to the study of light. Optics has subfields they are quantum optics, geometrical optics, and physical optics. Photonics refers to a subset of the optics discipline. The simplicity, high efficiency, reliability, transparency, and robust feature of PID controllers were few factors behind the reasons for its acceptance and more popularity for control in processing industries globally. All the conventional techniques for PID controller design and tuning offer early workable values for reaching favorable performances. The manual tuning of the PID controller variables becomes a difficult role that needs comprehensive knowledge and expertise in that field. Certain meta-heuristic techniques are explored to design PID controllers with the main aims of attaining minimum overshoot in lesser settling time and steady state response. For accomplishing enhanced robustness, minimization of disturbance elimination, operating, and physical restraints are treated as multi-optics functions. Therefore, this article presents a modified honey badger optimization (MoHBO) algorithm-based parameter tuning of the PID controller for optics and photonics. The tuning of the PID controller with constraints on the relative delay margin was considered an optimum disturbance rejection issue and summarized the tuning process. The presented MoHBO algorithm is derived by the inclusion of oppositional based learning (OBL) with standard HBO algorithm. In addition, the MoHBO algorithm is tested using the Magnetic Levitation System (MLS) and Phase Locked Loop system (PLL) to assure the enhanced robust nature of the PID controller. A wide ranging comparison study with other metaheuristic optimization algorithms demonstrates the better performance of the MoHBO algorithm over recent algorithms. [ABSTRACT FROM AUTHOR]

This article presents a systematic procedure to shape the body of an electrically large object in order to achieve a desired radiation/scattering pattern. In particular, the object surface is described by non‐uniform rational B‐splines (NURBS) and physical optics (PO) is used for electromagnetic field calculations. The NURBS control points and weights are considered as degrees of freedom for an evolutionary optimization algorithm. They are iteratively optimized according to the specific constraints of radiation/scattering problem under consideration. To speedup the optimization process, the electromagnetic codes are implemented on graphics processing unit (GPU). The accuracy of the simulation results are verified by CST commercial electromagnetic software. Furthermore, the results show simulation speedup on the order of several times to a few tens of times. This makes an iterative optimization of a surface rather practical on a single personal computer. [ABSTRACT FROM AUTHOR]

A compact antenna test range (CATR) system based on a planner stepped‐edged reflectarray antenna is proposed in this article. The parameters of the reflectarray antenna are determined by the design method of a single reflector system. Physical Optics (PO) method is used to calculate the unit phase of the reflectarray. The performance of the quiet zone is improved by optimizing the array shape. A 4320‐element reflectarray antenna with a dual‐ring structure is proposed and fabricated. The measured results show that the amplitude distribution of the designed reflectarray compact range is within ±1 dB, the phase distribution is within ±10°, and the cross‐polarization isolations are greater than 24 dB in the region of 50% at 10 GHz. The performance of the quiet zone is favorable for the usage of CATR systems. [ABSTRACT FROM AUTHOR]

Soft X-ray monochromators for synchrotron radiation sources have been continuously developed over the years, improving energy resolution and stability. Great effort has been made in improving the surface quality of the optics involved, reaching values permitting diffraction-limited images. Still, one problem has not been solved, nor fully understood, yet: groove placing errors. Nowadays, these are one of the major factors responsible for resolving the power reduction of diffraction-gratings-based X-ray monochromators. Despite decades of use of gratings, there is not yet a universally established method for predicting and simulating the effect of groove placing errors on monochromator performance. This is especially important in the new scenario of high-coherent X-ray sources, i.e. diffraction-limited storage rings and free-electron lasers. To address this problem, in this article an approach based on WISER (Wavefront propagatIon Simulation codE libRary) is presented. WISER is a physical optics simulation package, also available in the user-friendly Orange Synchrotron Radiation Suite - OASYS. Even though it was originally conceived to assess the focusing performance of X-ray mirrors in the presence of height defects, it perfectly simulates the performance of a periodic (or quasi-periodic) structure like a diffraction grating. In this article, the way to use WISER and its application to a specific case, e.g. the design of a monochromator for the upgrade of a beamline at the Advanced Light Source, are shown. A simple rule for estimating how well the grooves are placed on a grating, based on calculation of the Strehl ratio, is also presented. [ABSTRACT FROM AUTHOR]

Visibility status determination for every mesh element/edge with respect to an illuminating source is routinely required in mesh-based physical optics (PO) methods, where the scatterer is represented by subwavelength sized elements. This article presents an optimally efficient shadowing determination algorithm for both plane wave and point source (Hertzian dipole) illumination of large-scale triangle meshes. It is based on a recursive multilevel field-of-view (image space) subdivision buffer approach, whereby a point’s status is determined by only checking against a small subset of elements. It is error-free and formulated to maintain efficiency for inhomogeneous meshes and grazing incidence, which result in concentration of projected elements in small areas of the buffer plane. A key step is to separate the grazing and nongrazing parts of the mesh. Very challenging test cases affirm the algorithm’s expected optimal and robust linear computational cost scaling of $\mathcal {O}(N)$ , where $N$ denotes the number of mesh elements. For fixed $N$ , almost constant runtimes under extreme illumination and mesh variations, further demonstrate robustness. [ABSTRACT FROM AUTHOR]

We demonstrate theoretically coherent optical propagation in a composite photonic-molecule-cavity optomechanical system consisting of two whispering-gallery microcavities in which one of the optical cavities is optomechanical with high cavity dissipation and the other is an auxiliary with a high quality factor. Optomechanically induced transparency and its related propagation properties such as fast and slow light effects are investigated based on the hybrid system for suitable parametric regimes. By controlling the coupling strength J between the two cavities, which is determined by their distance and the decay rate ratio δ of the two cavities, tunable and controllable fast-to-slow light propagation (or vice versa) can be achieved. Our study may provide a further insight of the composite photonic-molecule optomechanical systems and may open up promising on-chip applications in quantum information processing. [ABSTRACT FROM AUTHOR]

This document is an editorial preface for a collection of articles on computational imaging for biophotonics and biomedicine. Computational imaging involves the joint design of optics and signal processing to extract images from raw data. It can perform multimodal imaging and enhance image resolution and contrast. The integration of computational imaging with artificial intelligence and machine learning is a key trend, enabling automation and new applications in fields like medical imaging. Computational imaging has the potential to revolutionize biophotonics and biomedicine by providing comprehensive, accurate, and non-invasive imaging for research, diagnosis, and monitoring. [Extracted from the article]

Hybrid and asymptotic methods of diffraction theory used when the electric size of a scatterer is large are based on the use of a solution for the radiation pattern of a cylindrical wave, which appears when a plane wave is scattered by an edge with a given boundary condition. The expression of the radiation pattern of a wave scattered by the edge of a half-plane with generalized semitransparent boundary conditions has not been obtained using the Sommerfeld integral technique. The use of the solution for the semitransparent case allows us to expand the asymptotic methods to scatterers with semitransparent edges. In this article, based on solving the problem of the scattering of a plane wave by a half-plane with the generalized semitransparent boundary conditions using the Sommerfeld integral technique, we derive a solution for the far-field of the cylindrical wave scattered by the semitransparent edge. Based on the obtained solution, we derive an expression for the calculation of an amendment to the physical optics approximation, which allows us to extend the physical theory of diffraction method to scatterers with semitransparent edges. We apply the uniform asymptotic theory of diffraction method to the problem of cylindrical-wave scattering by the semitransparent half-plane. [ABSTRACT FROM AUTHOR]

The depolarization ratio and backscattering cross sections have been calculated for shapes and size of ice crystals that are typical in cirrus clouds. The calculations are performed in the physical-optics approximation. It is shown that the depolarization ratio approaches some constant when the size of the crystals becomes much larger than the incident wavelength. For the transparent ice crystals, when absorption is absent, the magnitude of this constant strongly depends on crystal shapes. This fact allows inferring the crystal shape from magnitudes of the depolarization ratio in lidar signals. For the lidar wavelengths, where absorption of light is considerable, the depolarization ratio of lidar signals can be used for inferring crystal sizes. Such results are important for the development of algorithms interpreting the signals obtained by both ground-based and space-borne lidars. [ABSTRACT FROM AUTHOR]

This communication provides a novel adaptive irregular grid model (AIGM) to improve the scattering simulation efficiency of electrically large terrains. This model distinguishes the steep and flat regions of the measured topographic point cloud models by a threshold. To determine the optimal threshold, we present the height gradient as the criterion to describe the topographic undulation. The optimal threshold is located at the inflection point of the curve describing topographic similarity in the range of height gradient. This generated AIGM can reduce the grid quantity and maintain consistency with the original point cloud model. It is also valuable in the popular coherent and incoherent (C&I) scattering model of global navigation satellite system reflectometry (GNSS-R). In this communication, the coherent component can be expressed by a simple product of the electric field of the conductor grid, the characteristic function of roughness, and the Fresnel reflection coefficient. The incoherent component comes from the diffuse scattering simulated by the integral equation method (IEM). Compared with the traditional solution to C&I scattering by using the Kirchhoff approximation (KA), the modified C&I model has a more extensive application. The precision of the AIGM-based-C&I model is verified by traditional physical optics (PO). The excellent simulation efficiency of the AIGM-based-C&I model is also demonstrated. [ABSTRACT FROM AUTHOR]

Due to that the polarization scattering matrices (PSM) of single reflection (SR), double reflection (DR), and single diffraction (SD) at different angles are ignored, the PSM of trihedral corner reflector (TCR) is usually assumed to be [1 0; 0 1], which results in inaccuracy by utilizing its polarization to antijamming. Therefore, this article comprehensively analyzes the PSM of TCR based on high-frequency approximation. First, we separately analyze various reflection components based on the physical optics (PO)-shooting bouncing ray (SBR) model, so as to cure the deficiency that the classification discussion methods are susceptible to changes in target size and shape. Then, the PSMs of SR, DR, triple reflection, and SD are rigorously deduced and demonstrated by combining amplitude/phase information. In this process, we successfully integrate the six kinds of DR by the transforming of polarization base. Subsequently, the PSMs in the 2-D space are extended into the 3-D space, which are more suitable for the polarization characteristics of TCR. Finally, we compare the model in this article with the method of moment (MoM) of Feko software and obviously accelerate the model in this article through compute unified device architecture (CUDA). The conclusion of this article is significant for the polarization analysis of TCR to antijamming. [ABSTRACT FROM AUTHOR]

The multilevel fast multipole algorithm (MLFMA) is often used to speed up the solution of surface integral equations in electromagnetics. The method makes it possible to calculate electrodynamic systems with characteristic sizes of hundreds of wavelengths on a personal computer in a relatively short time (a few hours). The paper demonstrates the use of the MLFMA together with the principle of physical optics for fast calculation of microwave radiation between the elements of the mirror transmission lines. The complexity of the calculation is O(NlogN), where N is the number of elementary parts of the mirror surfaces involved in the calculation. Thus, the calculation time for a transmission line with characteristic total mirror sizes of hundreds of wavelengths is a few minutes. By using this method, it is also possible to significantly speed up the calculation of fields in oversized transmission lines, including both waveguides and mirrors, without loss of accuracy. [ABSTRACT FROM AUTHOR]

An efficient iterative hybrid multilevel fast multipole algorithm (MLFMA) and the physical optics (PO) is presented to efficiently analyze the large size antenna mounted on the electrically large platform, in which, the MLFMA is used to accelerate the impedance matrix–vector multiply procedure of method of moment (MoM) and the PO is employed to simulate the large platform. In this hybrid scheme, to overcome the computational cost required in the evaluation of the electrically large PO region contribution to the MLFMA region, the strategy of the efficient iterative MoM‐PO (EI‐MoM‐PO) is employed. In addition, the electrically large PO region shadowing effect coefficient will be checked before the computation of PO current, then the coefficient will be stored in bit format by using the Bitmap index method which is general enough to reduce the CPU time and memory consumption. The combination of EI‐MLFMA‐PO and Bitmap assists us to construct a proposed method that can reduce the computation cost dramatically and obtain good accuracy. Several examples are demonstrated to validate and prove the accuracy and efficiency of our method compared with the hybrid MLFMA‐PO method in FEKO. [ABSTRACT FROM AUTHOR]

The target scattering characteristics in microwave band are necessary to be researched for Orbital‐Angular‐Momentum (OAM) wave‐based radar applications. A theoretical description of electromagnetic (EM) scattering from a typical target by OAM waves is proposed in this paper. First, OAM waves are decomposed into plane waves in the spectral domain with different elevation and azimuth angles. Then, the scattering form of each decomposed plane wave is determined through coordinate system transformation and physical optics approximation. Formulas and numerical results are presented for OAM‐based radar scattering cross section of a perfect electric conductor and dielectric plate and a cylinder. Unlike the conventional results of EM plane wave scattering, the scattering properties of OAM waves from plate and cylinder are analysed with particular emphasis on OAM mode influence. The results provide insights into OAM wave‐matter interactions and may find important applications in wave propagation and OAM wave‐based radar detection and imaging. [ABSTRACT FROM AUTHOR]

A plane-wave spectrum method is presented for the fast computation of radiation integrals for source and observation plates, which can be arbitrarily tilted and separated by an intermediate-to-far-field distance. The method expedites the direct and inverse transforms between spatial and spectral domains using unequally spaced fast Laplace transforms. These fast algorithms allow one to combine fast Fourier transforms (FFTs) and contour deformation in the complex plane with controllable accuracy and computation times close to that of a single 2-D FFT. Hence, scattering interactions between plates of sizes up to thousands of wavelengths can now be computed within seconds using current desktop computers. The fast method is validated here for the case of radio propagation in a canyon street modeled with electrically large facets using the physical optics approximation. [ABSTRACT FROM AUTHOR]

The paper considers a physical optics model based on the Kirchhoff–MacDonald approximation taking into account re-reflections for solving electromagnetic-wave scattering problems. This model uses an integral representation of the electromagnetic field via surface currents. The paper describes an iterative algorithm in which, at each iteration step, the surface currents on the surface partition cells is determined by multiplying the influence matrix by the currents found at the previous iteration. To increase the computational efficiency of the algorithm, the influence matrix is compressed using the method of mosaic-skeleton approximations. In this case, the specificity of the matrix being approximated is taken into account by determining its elements via the matrix of the discrete representation of the integral operator, which contains the matrix of "visibility" of the partition cells. The visibility matrix indicates whether the segment connecting the centers of two cells intersects the illuminated surface at its internal points. The method was tested on model problems, which showed the applicability of the proposed algorithm to solving the problems of scattering by non-convex bodies, as well as the computational efficiency of the algorithm. [ABSTRACT FROM AUTHOR]

This study estimated raindrop size distribution (DSD) and rainfall intensity with an infrared surveillance camera in dark conditions. Accordingly, rain streaks were extracted using a k-nearest neighbor (KNN)-based algorithm. The rainfall intensity was estimated using DSD based on physical optics analysis. The estimated DSD was verified using a disdrometer. Furthermore, a tipping-bucket rain gauge was used for comparison. The results are summarized as follows. First, a KNN-based algorithm can accurately recognize rain streaks from complex backgrounds captured by the camera. Second, the number concentration of raindrops obtained through closed-circuit television (CCTV) images was similar to the actual PArticle SIze and VELocity (PARSIVEL)-observed number concentration in the 0.5 to 1.5 mm section. Third, maximum raindrop diameter and the number concentration of 1 mm or less produced similar results during the period with a high ratio of diameters of 3 mm or less. Finally, after comparing with the 15-min cumulative PARSIVEL rain rate, the mean absolute percent error (MAPE) was 44 %. The differences according to rain rate can be determined. The MAPE was 32 % at a rain rate of less than 2 mm h-1 and 73 % at a rate above 2 mm h-1. We confirmed the possibility of estimating an image-based DSD and rain rate obtained based on low-cost equipment during dark conditions. [ABSTRACT FROM AUTHOR]

All elements of the scattering matrix have been numerically studied for particles of irregular shapes whose size is much larger than incident wavelength. The calculations are performed in the physical optics approximation for a particle size of 20 μm at a wavelength of 0.532 μm. Here the scattered intensity reveals the backscattering coherent peak. It is shown that the polarization elements of the matrix reveal the surges within the backscattering peak. The angular width of the surges does not practically depend on particle shape, but depends on the particle size. It is shown that these surges are created by interference between the conjugate scattered waves propagating in the inverse directions. The results obtained are of interest for interpretation of lidar measurements in cirrus clouds. [ABSTRACT FROM AUTHOR]

This paper presents a passive bistatic radar (PBR) configuration using a global navigation satellite system as an illuminator of opportunity for the rotor blade feature extraction of a helicopter. Aiming at the strong fixed clutter in the surveillance channel of the PBR, a novel iteration clutter elimination method-based singular-value decomposition approach is proposed. Instead of the range elimination method used in the classic extended cancellation algorithm, the proposed clutter elimination method distinguishes the clutter using the largest singular value and by remove this value. At the same time, the fuselage echo of the hovering helicopter can also be suppressed along with the ground clutter, then the rotor echo of this can be obtained. In the micro-motion feature extraction, the mathematic principle of the flash generation process in the time–frequency distribution (TFD) is derived first. Next, the phase compensation method is applied to achieve the time–frequency flash shift in the TFD. After this, the center frequencies of the standard flashes in the TFD are compared with the standard frequency dictionary. The mean l1 norm is utilized to estimate the feature parameters of the helicopter rotor. In the experiments, the scattering point model and the physical optics facet model demonstrate that the proposed method can obtain more accurate parameter estimation results than some classic algorithms. [ABSTRACT FROM AUTHOR]