Effect Of Incidence Angle Research Articles

An exploration, analysis, and correction of the distance effect on terrestrial hyperspectral LiDAR data

Terrestrial hyperspectral light detection and ranging (LiDAR) (HSL), as one novel LiDAR system integrated with more wavelengths, has supplied enhanced possibilities in many fields by delivering the geographic coordinate and the hyperspectral backscattered intensity simultaneously. However, like the traditional single-wavelength LiDAR, it is faced with the distance effect, which restricts the accurate acquisition of the hyperspectral intensities and the quantitative retrieval of characteristics of the targets. The previously reported distance effect correction models mainly concentrated on the distance effect correction for the single-wavelength LiDAR system, and some normalization methods with the standard reflectance panel were also provided to calibrate the data measured by multispectral LiDAR and HSL, producing the reflectance-related value. Nevertheless, it is valuable to systematically explore the distance effect of HSL over long distances and search for the corresponding correction methods. Along these lines, in this study, the homogeneous targets and standard reflectance panels with different reflectance values were employed to participate in the distance experiment to systematically explore and analyze the distance effect phenomenon on terrestrial HSL data. A novel practical piecewise fitting model was proposed to output realistic correction results and it was also compared with the classic inverse distance square law and polynomial fitting model. To further demonstrate the feasibility and good capability, the models were employed in the intensity correction for the various vegetation leaf species. A simple 3-D scene experiment was then carried out to demonstrate the intensity variation before and after the implementation of the distance effect correction. From the acquired result, it suggests that (1) the distance effect on terrestrial HSL data is not related to the wavelength and the scanned target. All the wavelengths share a common distance effect; (2) the concept of the ‘distance effect function’ could represent well the distance effect for the terrestrial HSL; (3) as far as the correction ability is concerned, the proposed piecewise fitting model achieved better performance than the others because it exhibited the smallest standard deviation (σ), coefficient of variation (CV), and the ratio of the coefficient of variation (ε) for the correction results of the homogeneous targets, and the leaf experiments confirmed it again; and (4) the further 3-D experiment result exhibited the intensity variation. It proves that the distance effect does exist in the 3-D scanning results and the correction is necessary. Besides, for small-scanned scenes, the incidence angle effect dominates and largely affects the intensity data instead of the distance effect. This study enriches the study of the distance effect mechanism on the terrestrial HSL data, which facilitates the development of research on the radiative effect correction of the HSL. At the same time, the proposed model can be adopted for the analysis and correction of the distance effect on terrestrial HSL data in actual scanning tasks.

Reactive ion beam smoothing of rapidly solidified aluminum (RSA) 501 surfaces for potential visible and ultraviolet light applications

Optical elements made of aluminum with surface roughness in the sub-nanometer range are required for applications in the visible (VIS) and ultraviolet (UV) spectral range. Rapidly solidified aluminum (RSA) 501 is an interesting candidate to produce sufficiently smooth surfaces for these applications in an ultra-precision (UP) fly-cutting process. However, the polycrystalline grain structure and precipitates contained in the material limit the achievable surface roughness. In this research, a reactive ion beam finishing process of RSA 501 is investigated employing an electron cyclotron resonance (ECR)-driven ion source using CF4 and N2 gasses. Emphasis is placed on understanding the etching mechanisms that influence the topographic evolution to provide the basis for future production processes using the material for UV optics. Material composition characterization is applied to analyze the interaction between the reactive ion species and the RSA material. Surface modification transferring the native oxide top layer to an in situ forming and developing aluminum fluoride or -nitride etch front layer is found to prevent grain orientation-dependent etching. The effect of the ion incidence angle on the etch rates of precipitates and bulk material can be used to reduce the height of precipitates protruding from the surface after the UP-machining process. A surface roughness value of Sq = 0.9 nm ± 0.1 nm (areal root mean square height) is achieved in the micro-roughness range when etching at 40° and 80° angle of incidence using collimated ion beams with CF4 process gas.

Experimental Study of Wind Loads on Tubular Crossarms of Transmission Towers

The actions exerted by yawed wind on the crossarm substantially differ from those on the tower body due to the presence of the angle between the crossarm’s cross-section and the incoming flow, and this phenomenon deserves a better understanding. Focusing on the tubular crossarms with round-section members, this paper aims to determine insights into wind actions, as affected by various factors, such as the tower type, the mean width to mean height ratio, the solidity ratio, and the wind incidence angle, and thereby derive the wind loads for design. Accordingly, a succession of wind tunnel tests was conducted by using quadrilateral and triangular crossarm models with various solidity ratios and mean width to mean height ratios. The method of direct force measurement (DFM) is employed for the high frequency force balance (HFFB) test to attain the transverse and longitudinal forces on the crossarm simultaneously. It was found that the wind load coefficients increase with increases of the mean width to mean height ratio and decreases of the solidity ratio. Moreover, in the case of the incoming flow perpendicular to the crossarm face, it is concluded that compared to the quadrilateral crossarm, the triangular crossarm possesses a relatively smaller drag coefficient, provided a moderate mean width to mean height ratio of 1.19. Furthermore, an analysis of the experimental results shows that the skewed wind load factor specified in the relevant codes would overestimate the effects of the wind incidence angle and the variations in mean width to mean height ratio, which is evident in the tests but not considered in the codes. It is worth noting that the experimental results show that the crosswind force is pronounced, which is usually ignored in the skewed wind load factor-based approach. Comparatively, using wind load distribution factors seems to be more rational. Thus, the corresponding estimating equations are proposed for the wind load-distribution factors of the crossarms, which agree well with the experimental results. The developed equations would greatly facilitate the determination of wind loads on tubular crossarms.

Scattering of SH Waves by a Semi-cylindrical Bump in an Inhomogeneous Half-space

The wave propagation in an inhomogeneous half space with a semi-cylindrical surface bump is investigated by the means of complex function method. With the origin of the coordinate system as the center, the density of the medium changes radially. To solve the Helmholtz equation with variable coefficients caused by the inhomogeneous of the medium, a conformal transformation technique based on the theory of complex variable functions is adopted. Then, by adjusting the inhomogeneous parameters and comparing with the published analytical results, the correctness of the method in this paper is verified. Finally, the displacement amplitudes of typical observation points on the surface and inside are given, and the effects of incident wave angle, wave number and inhomogeneous parameters on wave energy distribution are analyzed.

Evaluation of Heat Flux Distribution on Flat Plate Compound Parabolic Concentrator With Different Geometric Indices

AbstractThe Compound Parabolic Concentrator (CPC), when coupled with the photovoltaic system, namely the Concentrated Photovoltaic Thermal System (CPVT), makes utilizing solar energy efficient. The major challenge that hinders the electrical and thermal performance of the CPC–CPVT system is the non-uniform heat flux distribution on the absorber surface. In the present paper, detailed ray-tracing simulations have been carried out to understand the heat flux distribution characteristics of CPC with different geometrical conditions, and those are concentration ratio, truncation ratio, incident angle, and average heat flux on the absorber surface. To have a thorough understanding, the analysis has been carried out in multiple steps. First, it is performed by analyzing the effect of concentration ratio and incident angle on heat flux distribution characteristics at a fixed truncation ratio. Second, investigations have been carried out to understand the heat flux distribution characteristics at different truncation ratios and different incident angles by keeping the concentration ratio constant. Local concentration ratio and non-uniformity index have been employed to quantify the non-uniformity of heat flux distribution on the absorber surface. It has been observed that the 0-deg incidence angle is the most effective angle to achieve uniform heat flux distribution on the absorber surface. This paper sheds insight into the heat flux distribution characteristics on the absorber surface of a CPC–CPVT system which can be used by the research community for designing an effective CPVT system from the perspective of uniform heat flux distribution on the absorber surface.

Numerical Investigation on Vortex-Induced Vibrations of Two Cylinders with Unequal Diameters

A series of numerical simulations of two-degree-of-freedom vortex-induced vibration of two coupled cylinders with unequal diameters are performed at the Reynolds number of 20,000. The effects of incident angle, spacing ratio, and diameter ratio on the VIV responses for two cylinders are investigated. It is shown that the lock-in range of the large cylinder is significantly widened and the maximum vibration amplitude decreases as a result of the existence of small cylinder. The mean drag coefficients and root mean square force coefficients of the large cylinder are not varied significantly with the incident angle and diameter ratio, but the force coefficients of the small cylinder vary considerably under different configurations. For the configuration of α = 0°, d/D = 0.05 and G/D = 0.05, the variations in vibration amplitude and frequency ratio are similar to those of the isolated cylinder. Different vortex shedding modes such as 2S mode, P+S mode, and 2P mode are observed for two coupled cylinders at different reduced velocities for different configurations.

An Improved Theoretical Model to Extract the Optical Conductivity of Two-Dimensional Material from Terahertz Transmission or Reflection Spectroscopy

The technique of terahertz time-domain spectroscopy (THz-TDS) enables us to simultaneously determine the real and imaginary parts of optical parameters. However, it is still a challenge to extract the optical parameters of a two-dimensional (2D) material (or an ultra-thin film) on a substrate accurately and flexibly for an arbitrary incident angle and different polarization. By treating a 2D material as a conductive boundary without thickness, we propose an improved theoretical model to extract the optical conductivity of the 2D material on a substrate from THz transmission or reflection spectroscopy. Importantly, the effects of wave polarization, incident angle, and multiple reflections in the substrate are considered in our model and the analytical formulae associated with the optical conductivity of the 2D material are provided. Furthermore, we verify the validation of our model based on the THz transmission and reflection experiments for mono- and few-layer MoS2 on sapphire substrates. These results not only are of practical significance for investigating the THz properties of 2D materials but can also be extended to the situations of ultra-thin films and/or incoherent detection such as Fourier transform infrared spectroscopy.

Optical performance analysis of InP nanostructures for photovoltaic applications.

In this article, we have performed a comparative analysis of six different types of nanostructures that can improve photon management for photovoltaic applications. These nanostructures act as anti-reflective structures by improving the absorption characteristics and tailoring the optoelectronic properties of the associated devices. The absorption enhancement in indium phosphide (InP) and silicon (Si) based cylindrical nanowires (CNWs) and rectangular nanowires (RNWs), truncated nanocones (TNCs), truncated nanopyramids (TNPs), inverted truncated nanocones (ITNCs), and inverted truncated nanopyramids (ITNPs) are computed using the finite element method (FEM) based commercial COMSOL Multiphysics package. The influence of geometrical dimensions of the investigated nanostructures such as period (P), diameter (D), width (W), filling ratio (FR), bottom W and D (W bot/D bot), and top W and D (W top/D top) on the optical performance are analyzed in detail. Optical short circuit current density (J sc) is computed using the absorption spectra. The results of numerical simulations indicate that InP nanostructures are optically superior to Si nanostructures. In addition to this, the InP TNP generates an optical short circuit current density (J sc) of 34.28 mA cm-2, which is ∼10 mA cm-2 higher than its Si counterpart. The effect of incident angle on the ultimate efficiency of the investigated nanostructures in transverse electric (TE) and transverse magnetic (TM) modes is also explored. Theoretical insights into the design strategies of different nanostructures proposed in this article will act as a benchmark for choosing the device dimensions of appropriate nanostructures for the fabrication of efficient photovoltaic devices.

A doped-polymer based porous silicon photonic crystal sensor for the detection of gamma-ray radiation.

In this research, a theoretical investigation of the one-dimensional defective photonic crystals is considered for the detection of gamma-ray radiation. Each unit cell of the considered one-dimensional photonic crystals (1D PhCs) is composed of two layers designed from porous silicon infiltrated by poly-vinyl alcohol polymer doped with crystal violet (CV) and carbol fuchsine (CF) dyes (doped-polymer) with different porosity. In addition, a single layer of doped-polymer is included in the middle of the designed 1D PhCs to stimulate the localization of a distinct resonant wavelength through the photonic band gap. In particular, the appearance of this resonant mode represents the backbone of our study towards the detection of γ-ray radiation with doses from 0 to 70 Gy. The Bruggeman's effective medium equation, the fitted experimental data to the refractive index of the doped-polymer, and the Transfers Matrix Method (TMM) serve as the mainstay of our theoretical treatment. The numerical findings provide significant contributions to some of the governing parameters such as the thicknesses of the considered materials on the performance of the presented sensor, the effect of incidence angle and the porosity of the considered materials on the resonance wavelength. In this regard, at optimum values of these parameters the sensitivity, quality factor, signal-to-noise ratio, detection limit, sensor resolution, and figure of merit that are obtained are 205.7906 nm RIU-1, 9380.483, 49.315, 2.05 × 10-5 RIU, 3.27 × 10-5, and 2429.31 RIU-1, respectively. Therefore, we believe that the suggested design could be of significant interest in many industrial, medical, and scientific applications.

A nonlinear static procedure for seismic assessment of unreinforced masonry buildings with rigid-diaphragms considering the effect of seismic incidence angle

A nonlinear static procedure for seismic assessment of unreinforced masonry buildings with rigid-diaphragms considering the effect of seismic incidence angle

Goniometric Examination of Diffuse Reflectance of a Skin Phantom in the Wavelength Range from 400 to 1600 nm

Since all of noninvasive optical monitors such as near-infrared spectroscopy are transcutaneous, it is important to consider the optical properties of the skin. The purpose of the present study was to clarify the effects of incident angle and source-detector separation (SDS) on the detection of components in the dermal layer. Here, we developed a novel skin phantom consisting of epidermal and dermal layers with optical properties ranging from 400 to 1600 nm. The phantom was simulated by only water, scatters and absorbers, without agarose, silicone or other materials. The phantom showed reflectance spectra very similar to those of actual human skin by the integrating sphere measurements. Furthermore, an optical system was assembled in which the incident angle could be changed from 20º to 80º and the SDS from 0 to 6 mm independently. For the wavelength range of 400 to 900 nm, the absorption spectrum of hemoglobin in the dermal layer was investigated to assess detectability. For the wavelength range of 900 to 1600 nm, the absorption spectrum was confirmed by including glucose in the dermal layer. The absorbance was calculated from the measured diffuse reflected light intensity. The optimal incident angle and SDS for optical measurements focused on the dermal layer were estimated by the signal-to-noise ratio (SNR). In the wavelength range of 400 to 900 nm, the absorption spectrum of hemoglobin with the highest SNR was obtained at an incident angle of 70° and SDS of 4 mm. In the wavelength range of 900 to 1600 nm, the absorption spectrum of glucose with the highest SNR was obtained at an incident angle of 20° and SDS of 0 mm. These conditions are expected to be optimal for transcutaneous measurement of biomolecules within the dermis using diffuse reflected light of wavelength range from 400 to 1600 nm.

The Absorption Properties of One‐Dimensional Spherical Photonic Crystals Based on Magnetized Ferrite Materials

AbstractBased on a spherical coordinate system and Maxwell's set of equations, the calculation formulas of one‐dimensional (1‐D) magnetized ferrite spherical photonic crystals (MFSPCs) are obtained and treated with the solution method of the spherical Bessel equations. Combined with the conventional transmission matrix method, expressions for the absorptance, reflectance, and transmittance of the 1‐D MFSPCs are given. 1‐D MFSPCs consisting of the general dielectric and Yttrium iron garnet (YIG) are also designed to verify the correctness of the conclusions. Variables such as external magnetic field, incidence angle, initial radius, and YIG thickness effects on the features of such 1‐D MFSPCs are also discussed. The transformation of the external magnetic field has a linear relationship with the position of the absorption band (AB). The three variables of incidence angle, initial radius, and YIG thickness have a substantial influence on the width and position of the AB, which can be adjusted according to the actual demand and are of high application significance. The results of this study can be helpful for the design of multifunctional absorbers and radome.

A Near-Infrared Plasmonic Sensor Based on Wedge Fiber-Optic for Ultra-Sensitive Hg Detection

The growing number of serious diseases caused by ever-increasing heavy metal ions pollution have necessitated the use of ion sensors in healthcare and environment monitoring systems. Even with low concentrations heavy metal ions can cause significant harm, so ultra-sensitive on-site and label-free monitoring of heavy metal ions is of great importance. In this work, a simple, portable and high sensitivity optical fiber surface plasmon resonance (SPR) sensor is demonstrated for the detection of Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> . On the basis of the investigation of the effects of different incident angles, the optical fiber sensor adopts wedged tip probe with a 75° incident angle. The plasmonic sensor exhibits a superior refractive index bulk sensitivity of up to 13830 nm/RIU in near-infrared band, which is a further step in ultrasensitive sensing detection, compared with the traditional optical fiber SPR sensors. In addition, we validate the optical fiber sensor's performance for Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> sensing. By self-assembling monolayer of 1,6-Hexanedithiol (HDT) on the sensing surface, the Au-coated fiber-optic probe is modified to capture Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> . The lowest detection limit is found to be 0.324 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf{ug}/\mathbf{mL}$</tex-math></inline-formula> for the near-infrared band and the sensitivity can reach up to 0.22 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$({\mathbf{ug}/\mathbf{mL}})$</tex-math></inline-formula> . The experimental results show the excellent promise for our sensor in applications of environmental monitoring due to high sensitivity, selectivity and low-cost.

Long wave absorption by a dual purpose Helmholtz resonance OWC breakwater

In this paper, a novel hybrid breakwater-WEC system consisting of a Helmholtz-resonance oscillating water column (OWC) caisson array and a perforated wall is proposed to attenuate long waves. The principle of Helmholtz-resonance OWC is analogous to the acoustic Helmholtz resonator for noise reduction. A semi-analytical model was developed based on potential flow theory using the matching eigenfunction method to investigate wave interaction with the OWC-breakwater system. The velocity singularity at the tip of the wall is resolved using the Galerkin method to improve the model convergence. The semi-analytical model of the present wave-air-structure interaction problem is verified using Haskind relation and energy conservation rule. Furthermore, we validate the model using numerical and experimental data in terms of wave reflection and wave power absorption. Hydrodynamic characteristics of the proposed hybrid breakwater-WEC system and the influence of key geometrical and wave parameters were investigated. Theoretical results indicate that long waves can be effectively absorbed by the OWC caisson through Helmholtz resonance for both normal and oblique waves. The resonance frequency of OWC varies with the chamber wall draft and chamber width in the along-shore direction. It was found that installing a perforated wall in front of the OWC array could broaden the frequency bandwidth of significant wave attenuation. The along-shore length of each OWC chamber ( 2l ) and the incident wave angle ( θ ) are identified as the key parameters that affect the hydrodynamic performance of the system at high frequency range due to the along-shore sloshing of water column, but have a relatively minor effect on long waves attenuation. The present OWC-breakwater system demonstrates advantage and superior performance over conventional rubble mound breakwaters and breakwaters of multiple perforated walls in attenuating long waves. The findings of this paper provide guidance for a novel design of breakwaters for absorbing long waves. • Novel Helmholtz-resonance OWC breakwater with a perforated wall is proposed to absorb longer waves．. • Semi-analytical model of wave interaction with OWC array with perforated wall is developed and validated．. • Present hybrid OWC-breakwater system is more effective in absorbing long waves than conventional breakwaters. • Significant effect of incident wave angle on wave reflection is observed at higher frequency range but not at low frequency range.

Individually frequency and amplitude tunable metamaterial absorber with sensing functions based on strontium titanate and graphene

A terahertz metamaterial absorber with sensing function based on strontium titanate (STO) and graphene is designed. The optical characteristics of the designed structures are simulated and numerically calculated by the finite difference time domain (FDTD) and coupled mode theory (CMT) method. The results show that the temperature of STO is 300 K and Fermi level of graphene is 1.0 eV, the absorptance achieves 99.8 % and 92.7 % at 0.36 THz and 2.18 THz, respectively. When the temperature of the STO is set from 250 K to 400 K, the center frequency is moved from 0.32 THz and 1.96 THz to 0.43 THz and 2.54 THz. When the temperature is stable at 300 K, the dual narrow band absorption can be converted to single narrow band absorption by tuning the Fermi level from 1.0 eV to 0 eV. The physical mechanism of the dual narrow band absorptions and active tuning is analyzed by electric field distribution and impedance matching theory. The effect of polarization direction and incident angle on the absorber performance is also investigated. In addition, we also investigated the sensing characteristics of the absorber when the Fermi level of graphene is 0 eV, and the sensitivity and figure of meritis of the structure for detecting different refractive indices is 50 GHz/RIU and 0.33/RIU. The proposed structure provides new ideas for future multifunctional terahertz device design.

Correlation between non-spectral and cumulative-based ground motion intensity measures and demands of structures under mainshock-aftershock seismic sequences considering the effects of incident angles

One of the pivotal steps in seismic assessment of structures is the definition of functional relationships between an Engineering Demand Parameter (EDP) and a ground motion Intensity Measure (IM). This paper investigates the correlation between widely used non-spectral and cumulative-based ground motion intensity measures and corresponding engineering demand parameters for regular and irregular structures as bidirectional single-degree-of-freedom (2D-SDOF) systems. The correlation is investigated under sequential earthquakes in terms of efficiency and sufficiency, considering various seismic incident angles. Structural performance is expressed as maximum inelastic displacement, MD, maximum inelastic absolute acceleration, MA, residual displacement, RD, and hysteretic energy, EH. The results of extensive parametric analyses show that if the MD, MA, EH and RD of regular systems are considered as demand parameters, the optimal IMs in terms of efficiency and sufficiency are vsq, arms, vrs and vsq, respectively.

Normalized Radar Scattering Section Simulation and Numerical Calculation of Freak Wave

The improved phase modulation method is used to numerically simulate a two-dimensional freak wave. While generating freak waves at specific positions, the spectral structure of the target spectrum can also be maintained, and the statistical characteristics of wave sequences can be satisfied. The numerical simulation process is discussed in detail from the perspective of different wave spectra and other parameters, the priority applicability of the Joint North Sea Wave Project (JONSAWP) spectrum is determined, and the accuracy of the numerical simulation is significantly improved. At the same time, the electromagnetic scattering characteristics of freak waves are studied based on the two-scale method (TSM). The calculation results of normalized radar cross section (NRCS) under different wave spectra and different polarization modes are compared, and the effects of wind speed, incident frequency, and incident angle on the calculation results are discussed. Experiments show that the NRCS of the freak wave is obviously lower than the background wave, and the calculation of the NRCS is relatively simple. This provides an effective reference for radar detection of freak waves in offshore engineering.

Simulation of an Indoor Visible Light Communication System Using Optisystem

Visible light communication (VLC ) is an emerging research area in wireless communication. The system works the same way as optical fiber-based communication systems. However, the VLC system uses free space as its transmission medium. The invention of the light-emitting diode (LED) significantly updated the technologies used in modern communication systems. In VLC, the LED acts as a transmitter and sends data in the form of light when the receiver is in the line of sight (LOS) condition. The VLC system sends data by blinking the light at high speed, which is challenging to identify by human eyes. The detector receives the flashlight at high speed and decodes the transmitted data. One significant advantage of the VLC system over other communication systems is that it is easy to implement using an LED and a photodiode or phototransistor. The system is economical, compact, inexpensive, small, low power, prevents radio interference, and eliminates the need for broadcast rights and buried cables. In this paper, we investigate the performance of an indoor VLC system using Optisystem simulation software. We simulated an indoor VLC system using LOS and non-line-of-sight (NLOS) propagation models. Our simulation analyzes the LOS propagation model by considering the direct path with a single LED as a transmitter. The NLOS propagation model-based VLC system analyses two scenarios by considering single and dual LEDs as its transmitter. The effect of incident and irradiance angles in an LOS propagation model and an eye diagram of LOS/NLOS models are investigated to identify the signal distortion. We also analyzed the impact of the field of view (FOV) of an NLOS propagation model using a single LED as a transmitter and estimated the bitrate (Rb). Our theoretical results show that the system simulated in this paper achieved bitrates in the range of 2.1208×107 to 4.2147×107 bits/s when the FOV changes from 30∘ to 90∘. A VLC hardware design is further considered for real-time implementations. Our VLC hardware system achieved an average of 70% data recovery rate in the LOS propagation model and a 40% data recovery rate in the NLOS propagation model. This paper’s analysis shows that our simulated VLC results are technically beneficial in real-world VLC systems.

Evaluation of Multi-Incidence Angle Polarimetric Gaofen-3 SAR Wave Mode Data for Significant Wave Height Retrieval

Significant wave height (SWH) is one of the most important descriptors for ocean wave fields. The polynomial regression (PolR) and Gaussian process regression (GPR) models are implemented to explore the effects of polarization and incidence angles on the SWH estimation from multi-incidence angle quad-polarization Gaofen-3 SAR wave mode data, based on the collocated data set of approximately 12,000 Gaofen-3 wave mode imagettes, matched with SWH from the fifth generation reanalysis (ERA5) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The results show that the model performance improves, as long as polarimetry information increases. The hybrid polarizations perform stronger than the co-polarizations or cross-polarizations alone, and they show better performance over the low to high seas. The lower incidence angles are more favorable for SAR SWH inversion. It is superior to introduce incidence angle in piecewise way, rather than to include it as an independent variable in the models. Then, the final PolR and GPR models, with the superior input scheme that includes the quad-polarized features and introduces the incidence angle in piecewise way, are assessed independently through a comparison with observations from altimeter and buoys. The accuracies of our SWH estimates are comparable or even higher than other published results. The GPR model outperforms the PolR model, due to the superiority of the added nonlinearity of GPR.

Novel optical behaviors of metamaterial and polymer-based ternary photonic crystal with lossless and lossy features

In this simulation work, we analyze a ternary photonic crystal composed of polymer, metamaterial and Silicon with the help of simple transfer matrix method. First, it is noted that there exist three regions for the metamaterial in the frequency range 0 –10 GHz, namely as DNG, SNG, and DPS regions. In this investigation, we focus on the effects of incident angle, metamaterial thickness and electromagnetic damping, on the EM wave transmission. From the transmittance spectra obtained by TMM, it is observed that a wide PBG exists covering all these three regions at normal incidence, and it is enhanced with increase in the incident angle. It is found that at oblique incidences, the gap gets splitted into two components due to the existence of a splitting transmission line similar to defect mode, whose transmission is highly increased up to 1 at an incident angle above 75°. It is demonstrated that the splitting frequency increases with increase in the incident angle exhibiting a blue shift. The increase is monotonic and nonlinear, where the increase is more for larger thickness of the metamaterial. Further, on comparing the results obtained with electric and magnetic damping cases, it is found that a linear decrease in the transmittance corresponding to the peak frequency in the magnetic loss is dominant over the electric loss, where the PBG shows least dependence on the electric and magnetic damping frequency. These insights of the paper may be exploited to fabricate metamaterial-based devices, split-ring resonators, sensors, microwave antennas, super-lenses, clocking, and switching devices.