Effect Of Incidence Angle Research Articles

A PET detector module with monolithic crystal, single end readout, SiPM array and high depth-of-interaction resolution

Depth of interaction (DOI) technology can improve the spatial resolution of nuclear medicine imaging system which uses scintillation detectors such as Positron Emission Tomography (PET). In this paper, a prototype detector module with DOI capability is established to make complementary characteristic tests on an existing method and to improve the experimental performance using the same method. We investigate the gamma incident surface and incident angle effects on the positioning method with our model in simulations and evaluate its 3-D positioning results in experiment. It shows that the positioning results are highly affected by the gamma incident surface and incident angle. The 137Cs energy resolution is 12.1% and the DOI resolution is estimated at 2.26 mm in average by our detector in experiment.

Study of the incidence angle effect on the aerodynamic structure characteristics of an incurved Savonius wind rotor placed in a wind tunnel

In this paper, we are interested on the study of the incidence angle effect on the aerodynamic structure of an incurved Savonius wind rotor. The numerical model is based on the resolution of the Navier-Stokes equations in conjunction with the standard k-ε turbulence model. These equations were solved by a finite volume discretization method. The software “Solidworks Flow simulation” has been used to characterise the flow characteristics in different transverse and longitudinal planes. To confirm the computer method validity, an experimental validation has been done using a wind tunnel equipped by the incurved Savonius wind rotor.

A method for controlled target strength measurements of pelagic fish, with application to European anchovy (Engraulis encrasicolus)

Abstract Measuring fish target strength (TS) in the wild is challenging because: (i) TS varies versus physical (orientation relative to the incident sound wave, size, and depth) and physiological fish attributes (maturity and condition), (ii) the target species and its aforementioned attributes are difficult to assess in near real time, and (iii) in the case of packed fish schools, accepted echoes may originate from multiple unresolved targets. We propose a method for controlled TS measurements of densely packed small pelagic fish during daytime, based on the joint use of a Remotely Operated Towed Vehicle, “EROC”, with a pelagic trawl fitted with a codend opening system, “ENROL”. EROC, equipped with a 70-kHz split-beam echosounder (Simrad EK60) and a low-light black and white camera, can be moved inside the fishing trawl. Pelagic fish are funnelled into the open trawl and their TS is measured in the middle of the net, where small groups actively swim towards the trawl mouth. The swimming behaviour allows for near-dorsal TS to be measured, minimizing the large effect of incidence angle on TS variability. The EROC camera, located near the open codend, provides optical identification of the species. This method was used to measure the TS of European Anchovy, Engraulis encrasicolus in the Bay of Biscay during 2014. The mean, near dorsal TS was −43.3 dB, for a mean fork length of 12.5 cm. This value is compared to published values of clupeiforms mean TS obtained for a range of natural incidence angles and discussed in the light of TS modelling results obtained for E. encrasicolus.

Investigation of ellipsometric parameters of 2D microrough surfaces by FDTD.

Ellipsometry is a powerful method for measuring the optical constants of materials and is very sensitive to surface roughness. In previous ellipsometric measurement of optical constants of solid materials with rough surfaces, researchers frequently used effective medium approximation (EMA) with roughness already known to fit the complex refractive index of the material. However, the ignored correlation length, the other important parameter of rough surfaces, will definitely result in fitting errors. Hence it is necessary to consider the influence of surface roughness and correlation length on the ellipsometric parameters Δ (phase difference) and Ψ (azimuth) characterizing practical systems. In this paper, the influence of roughness of two-dimensional randomly microrough surfaces (relative roughness σ/λ ranges from 0.001 to 0.025) of silicon on ellipsometric parameters was simulated by the finite-difference time-domain method which was validated with experimental results. The effects of incident angle, relative roughness, and correlation length were numerically investigated for two-dimensional Gaussian distributed randomly microrough surfaces, respectively. The simulated results showed that compared with the smooth surface, only tiny changes of the ellipsometric parameter Δ could be observed for microrough silicon surface in the vicinity of the Brewster angle, but obviously changes of Ψ occur especially in the vicinity of the Brewster angle. More differences between the ellipsometric parameters of the rough surface and smooth surface can been seen especially in the vicinity of the Brewster angle as the relative roughness σ/λ increases or correlation length τ decreases. The results reveal that when we measure the optical constants of solid materials by ellipsometry, the smaller roughness, larger correlation length and larger incident wavelength will lead to the higher precision of measurements.

A note on the optic characteristics of daylighting system via PMMA fibers

Polymethylmethacrylate (PMMA) plastic fiber has been used in daylighting system for a long time, however, the quantitative study of its optical properties is still limited. It has been verified in this paper that shortpass dichroic mirror (SDM) can effectively filter out up to 64% of infrared ray from high flux, resulting in small losses of visible spectrum of natural light. Experiments confirmed as well that SDM can significantly reduce infrared thermal effects effectively protecting PMMA plastic fiber. In addition, the effect of incidence angle on the attenuation of fiber is also measured. It has been proven that attenuation rate increases with the incident angle. Experimental data presented here can be used for daylighting system optimization using PMMA fibers.

Study of radiative transfer in 1D densely packed bed layer containing absorbing–scattering spherical particles

In this study, transmission process of diffused and collimated beam in a 1D densely packed bed is investigated. Absorbing–scattering spherical particles with the same radius are distributed randomly in transparent and absorbing host media. The refractive indexes of the spheres are different from that of the host medium. The size parameter χ of these spheres is sufficiently large to simulate their interaction with radiation through a Monte Carlo ray-tracing technique based on the geometrical optics approximation. Using the validation of the code for radiative transfer in a single absorbing–scattering sphere and in a packed bed filled with opaque or absorbing spheres, the effects of albedo, optical thickness, refractive index, and incident angle on the transmission process are examined in detail. The information of transmittance, reflectance, bidirectional reflectance distribution function (BRDF) and bidirectional transmittance distribution function (BTDF) are employed to describe the role of absorbing–scattering spheres in transparent and absorbing host media.

Oblique wave scattering by a semi-infinite elastic plate with finite draft floating on a step topography

On the basis of a potential theory and Euler-Bernoulli beam theory, an analytical solution for oblique wave scattering by a semi-infinite elastic plate with finite draft floating on a step topography is developed using matched eigenfunction expansions. Different from previous studies, the effects of a wave incident angle, a plate draft, three different plate edge conditions (free, simply supported and built-in) and a sea-bottom topography are all taken into account. Moreover, the plate edge conditions are directly incorporated into linear algebraic equations for determining unknown expansion coefficients in velocity potentials, which leads to a simple and efficient solving procedure. Numerical results show that the convergence of the present solution is good, and an energy conservation relation is well satisfied. Also, the present predictions are in good agreement with known results for special cases. The effects of the wave incident angle, the plate draft, the plate edge conditions and the sea-bottom topography on various hydrodynamic quantities are analyzed. Some useful results are presented for engineering designs.

Design of a broadband electromagnetic absorbers based on TiO2/Al2O3 ceramic coatings with metamaterial surfaces

This paper presents a design method of wide-band radar absorber (RA) based on TiO2/Al2O3 ceramic coatings with metamaterial surfaces. The metamaterial surfaces are made up of periodic array of metallic patches consisting of circular and square aluminum film. The effects of design parameters on the reflectivity of RA were discussed, including the size, the period of metamaterial surfaces, and the thickness of ceramic coating. In addition, the effects of incidence angles for transverse electromagnetic (TE) and transverse magnetic (TM) polarization on the microwave absorption properties of RA were also investigated. Simulated results indicated that the microwave absorbing properties can be improved and adjusted by selecting the suitable unit dimensions of metamaterial surfaces, the RL is generally insensitive to incident angle from 0° to 30°. Finally, the design parameters of RA were optimized by Genetic Algorithms (GA) approach under normal incidence. Both the simulated results and measured results indicated that a bandwidth of reflection loss (RL) of single TiO2/Al2O3 ceramic coating below −10 dB is 0 GHz in the frequency range of X-band and Ku-band. By combination of metamaterial surfaces to ceramic coatings, a bandwidth with the reflectivity of RA below −10 dB can be obtained in the frequency range of 8.2–18 GHz for the thickness of the TiO2/Al2O3 coating of only 1.7 mm. The minimum value of reflection loss is −29 dB at about 10.6 GHz.

On the wake pattern of symmetric airfoils for different incidence angles at Re = 1000

In the current study, numerical simulations are performed in order to investigate effects of incidence angle and airfoil thickness on alternating vortex pattern of symmetric airfoils at Re = 1000. This alternating vortex pattern is found to be significantly varying in shape as the incidence angle increases. The results are obtained with 1° increment from 0° to 41° and then with 10° increment from 40° until 180°. The instantaneous and mean vortex patterns are investigated around 2% thick (NACA 0002) and 12% thick (NACA 0012) airfoils. The mean lift, drag, and pitching moment coefficients in addition to Strouhal number are computed and compared with the results available in literature. It is found that the wake behind the airfoil exhibits a continuous vortex shedding pattern below 8° incidence angle for NACA 0002 and below 7° incidence angle for NACA 0012 at Re = 1000. The wake structures are classified into five different modes according to their pattern obtained from instantaneous and mean vorticity fields by also taking into account the amplitude spectrum of the lift coefficient, the instantaneous and mean aerodynamic force coefficients, velocity fields, and the longitudinal and lateral vortex spacings.

Assimilation of LAI and Dry Biomass Data From Optical and SAR Images Into an Agro-Meteorological Model to Estimate Soybean Yield

Crop monitoring at a fine scale and crop yield estimation are critical from an environmental perspective because they provide essential information to combine increased food production and sustainable management of agricultural landscapes. The aim of this article is to estimate soybean yield using an agro-meteorological model controlled by optical and/or synthetic aperture radar (SAR) multipolarized satellite images. Satellite and ground data were collected over seven working farms. Optical and SAR images were acquired by Formosat-2, Spot-4, Spot-5, and Radarsat-2 satellites during the soybean vegetation cycle. A vegetation index (NDVI) was derived from the optical images, and backscattering coefficients and polarimetric indicators were computed from full quad-pol Radarsat-2 images. An angular normalization of SAR data was performed to minimize the incidence angle effects on SAR signals by using the complementarities provided by SAR and optical data. The best results are obtained when the model is controlled by both the leaf area index (LAI) derived from the optical vegetation index modified triangular vegetation index (MTVI2) or from the SAR backscattering coefficient σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°VV</sub> (LAI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MTVI2</sub> or (LAI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VV</sub> ) and the dry biomass (DB) derived from the SAR Pauli matrix T33 (DB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T33</sub> )(r2 > 0.83), demonstrating the complementary of optical and SAR data.

Incidence Angle Correction of SAR Sea Ice Data Based on Locally Linear Mapping

Radar backscatter variations that occur because of incidence angle effects constrain the application of Scanning Synthetic Aperture Radar (ScanSAR) data for sea ice monitoring and observations. In this paper, a class-based correction is proposed for normalizing each class in ScanSAR data to a nominal incidence angle. Two tested sea ice synthetic aperture radar (SAR) data sets were acquired: a data set for the Gulf of Saint Lawrence, which was obtained by the RADARSAT-2 satellite, and a data set for the Bohai Sea, which was obtained by the ENVISAT Advanced Synthetic Aperture Radar. An unsupervised classification is performed on each image block prior to normalization, and the incidence angle range of each image block is approximately 5°. Because the distribution of the backscatter coefficients in the azimuth band is discrete and nonlinear, the class-based locally linear mapping (LLM) technique is implemented, based on the assumption that a small quantity of sorted backscatter coefficients is locally linear. This algorithm is a transplantable and easily applied method that requires limited ground data, and it is also a semiautomated technique because nearly all of its parameters can be adaptively determined during the image analysis. The results demonstrate that LLM-corrected ScanSAR images appear to have more detailed textures, and the natural signal variability in the radar data is preserved, which indicates that the LLM produces better results compared with the histogram-based-alike (HIST-alike) technique when correcting the incidence angle in the sea ice SAR data. The results of the data analysis in this paper show that the width of the azimuth band should be selected based on the extent of variation in the incidence angle, and the reference band can be calculated based on the maximum interclass distance principle. The intercomparisons also reveal that the proposed algorithm can improve the accuracy of supervised classifications.

Local incidence angle referenced classification on polarimetric synthetic aperture radar images in mountain glacier areas

The incidence angle is a crucial parameter for synthetic aperture radar (SAR). The local incidence angle differs greatly in mountainous areas, and it may lead to quite different backscatter properties for the same ground targets for different incidence angles. As a result, it has to be taken into consideration in image classification. This work demonstrates the importance of the local incidence angle and the necessity of considering this angle in SAR image classification in mountainous areas. A local incidence angle referenced method based on support vector machines is developed to perform classification. In this method, the datasets are divided into different zones according to local incidence angle, and the training and predicting are performed within these zones to eliminate the influence of the local incidence angles. The experiments are performed around the Dongkemadi Glacier in the central Qinghai-Tibetan plateau using two RADARSAT-2 polarimetric SAR images. This paper concentrates on the effect of the local incidence angles in SAR image classification. Compared to the method using only backscatter coefficients, the proposed method improves the overall classification accuracy by 6 to 8%. More important, it is verified that this method is more helpful for the ground cover types where the terrain changes sharply.

Effect of incident angle and polarization on electrically-tunable defect mode in anisotropic photonic crystals.

In this study, the effects of incident angle and state of wave polarization on electrically-tunable defect mode in a one-dimensional photonic crystal (1DPC) structure with an anisotropic defect layer is theoretically investigated. A 4×4 transfer matrix method is employed to calculate the transmittance spectrum of the structure with biased defect layer at different incident angles for TE and TM polarizations. The results indicate that at both polarizations, the peak wavelength of the defect mode shifts toward blue as the angle of incidence increases. Also, blue and red shifts can be observed in the defect mode for positive and negative biases, respectively. In addition, the defect mode compresses at TE (TM) polarization at negative (positive) biases and broadens for positive (negative) biases. A tunability defect mode may have potential application in the design of controllable optical filters in all optoelectronic devices.

Reflection and transmission properties of a metasurface composed of resonant loaded wire dipoles

A considered metasurface is assumed to consist of a two-dimensional periodic arrangement of inductively loaded wires. The effects of incident angles and inductive loads upon equivalent surface impedance, reflection, and transmission properties of this metasurface have been investigated using numerical simulations. It is shown that at a particular frequency and angle, a metasurface can be cloaked for the incoming incident wave with nearly zero reflection. It is further studied that this approximate zero reflection is independent of the inductances of the inductively loaded wire dipoles.

Effect of incident angle on crack propagation at interfaces

The effect of incident angle on crack deflection versus penetration has not been widely studied using a combined stress-and-energy criterion. This work does so by using a cohesive-zone method and dimensionless parameters. Results show deflection becomes more likely as angle decreases with greatest sensitivity to angular change at large angles. Deflection becomes increasingly strength-ratio dependent at small angles due to a shared crack-tip stress field. As fracture length scale decreases, deflection becomes more likely. Normalized toughness is shown to have a small effect on results. Significant is the insight provided on propagation behavior and the simplification in the use of a stress-and-energy criterion.

Optical properties of a grating-nanorod assembly structure for solar cells

This paper proposes a grating-nanorod assembly structure that can be applied to silicon solar cells. The optical properties of the assembly structure are examined by applying the finite difference time domain method in the 300–1100nm wavelength region, where the average spectral absorptance of the structure can reach 0.955. This high absorptance is attributed to guided mode resonance and microcavity effect. The transient and steady-state magnetic field distribution of the structure reveals the underlying mechanisms of such extraordinary phenomena. Absorptance is further investigated at different diameters and lengths of the nanorod component. The effects of incident angle on absorptance are also discussed. The solar cells of the structure can yield an optimum conversion efficiency of 25.91%. Thus, the proposed structure can be applied to silicon solar cells.

Research on quantum efficiency and photoemission characteristics of negative-electron-affinity GaN nanowire arrays photocathode

Based on studies about photon absorption, band structure, and electron transport, quantum efficiency formula of negative-electron-affinity (NEA) GaN nanowire arrays (NWAs) photocathode has been derived from one-dimension continuity equation. According to the formula, the quantum efficiency of NEA GaN NWAs photocathode is calculated. It reveals a satisfactory result that the quantum efficiency of NEA GaN NWAs photocathode can reach to 41 % in comparison to 25 % of the conventional reflection-mode GaN photocathode. Meanwhile, the effects of incident angle of entering light and the diameter of nanowire on the spectra response of NEA GaN NWAs photocathode are also investigated. Results suggest that the optimal incident angle is 47° and the optimal diameter is between 100 and 140 nm which is related to the absorption coefficient of different incident light wavelengths. In addition, with the decrease of surface reflectivity or the increase of surface electron escape probability, the photoemission characteristics of NEA GaN NWAs are enhanced. According to all simulated calculation, potential advantages of NEA GaN NWAs photocathode are discovered and NEA GaN NWAs photocathode with more reasonable structure and better performance becomes realizable in the application of electron sources.

Advancements for Snowmelt Monitoring by Means of Sentinel-1 SAR

The Sentinel satellite constellation series, developed and operated by the European Space Agency, represents the dedicated space component of the European Copernicus program, committed to long-term operational services in environment, climate and security. We developed, tested and evaluated an algorithm for generating maps of snowmelt area from C-band synthetic aperture radar (SAR) data of the Sentinel-1 mission. For snowmelt classification, a change detection method is applied, using multitemporal dual-polarized SAR data acquired in Interferometric Wide swath (IW) mode, the basic operation mode over land surfaces. Of particular benefit for wet snow retrievals are the high instrument stability, the high spatial resolution across the 250 km wide swath, and the short revisit time. In order to study the impact of polarization, we generated maps of melting snow using data of the VV-polarized channel, the VH-polarized channel and a combined VV- and VH-based channel using a weighting function that accounts for effects of the local incidence angle. Comparisons are performed with snow maps derived from Landsat images over study areas in the Alps and in Iceland. The pixel-by-pixel comparisons show good agreement between the snow products of the two sensors, with the best performance for retrievals based on the combined (VV and VH) channel and a minor decline for the VH-based product. The VV-based snowmelt extent product shows a drop-off in quality over areas with steep terrain because of the decreasing backscatter contrast of snow-covered versus snow-free surfaces on fore-slopes. The investigations demonstrate the excellent capability of the Sentinel-1 mission for operational monitoring of snowmelt areas.

Surface reflectance retrieval from the intensity data of a terrestrial laser scanner

The intensity data recorded by terrestrial laser scanning systems are considered significant measures of the spectral property of scanned objects. These data can be used in an extensive range of object-based applications. However, the direct retrieval of reflectance from intensity information is infeasible because intensity data are influenced by multiple variables, particularly distance and incidence angle. This study proposes a new method to recover the absolute reflectance value of the scanned surface by eliminating the effects of distance and incidence angle. The Faro Focus3D 120 terrestrial scanner is utilized in the case study. Two sets of experiments are designed to estimate the parameters of the developed model by using Lambertian targets at different reflectance values. With the estimated parameters, the proposed method is applied to recover the reflectance values of natural surfaces. The deviation of the retrieved reflectance values of natural surfaces from the reflectance values measured by a spectrometer is approximately 2.64%. Results show that the proposed method exhibits high accuracy in retrieving reflectance values and can be utilized for actual mapping tasks and geological applications.

Mixing Behaviors of Jets in Cross-Flow for Heat Recovery of Partial Oxidation Process

Abstract In our previous work, a new technology has been proposed that the cooled synthetic gas (syngas) produced in the partial oxidation process can be used as quenching medium. The mixing of the hot product gas and cold syngas is critical to this new quenching approach. In this work, both experimental measurements and CFD simulations were conducted to study the mixing behavior of the jets in cross-flow (JICF). A mixing apparatus with four jets was set up. Methane was used as the tracing gas and the concentration distribution was measured using an FID detector. The realizable k-ε model was found to give better predictions of the experimental data among the three k-ε models. The effects of jet incident angle θ, jet velocity to mainstream velocity ratio VR and Reynolds number on the mixing behavior were investigated. The results showed that the optimum jet incident angle was 145°. For configuration with jet incident angle smaller than 130°, increasing the velocity ratio VR in the range of 1–3 improves the mixing. When the jet incident angle is larger than 130°, the optimized range of velocity ratio VR is 1.8–2.4. The Reynolds number has insignificant effect on the spatial distribution of mixedness, indicating that the optimum design parameters obtained at low Reynolds number can be used to guide the choosing of industry operating conditions with Reynolds number as high as 3.13×105–6.26×105.