Different Angles Of Incidence Research Articles

Considering combined or separated roughness and vegetation effects in soil moisture retrievals

For more than six years, the Soil Moisture and Ocean Salinity (SMOS) mission has provided multi angular and full-polarization brightness temperature (TB) measurements at L-band. Geophysical products such as soil moisture (SM) and vegetation optical depth at nadir (τnad) are retrieved by an operational algorithm using TB observations at different angles of incidence and polarizations. However, the quality of the retrievals depends on several surface effects, such as vegetation, soil roughness and texture, etc. In the microwave forward emission model used in the retrievals (L-band Microwave Emission Model, L-MEB), soil roughness is modelled with a semi-empirical equation using four main parameters (Qr, Hr, Nrp, with p=H or V polarizations). At present, these parameters are calibrated with data provided by airborne studies and in situ measurements made at a local scale that is not necessarily representative of the large SMOS footprints (43km on average) at global scale. In this study, we evaluate the impact of the calibrated values of Nrp and Hr on the SM and τnad retrievals based on SMOS TB measurements (SMOS Level 3 product) over the Soil Climate Analysis Network (SCAN) network located in North America over five years (2011–2015). In this study, Qr was set equal to zero and we assumed that NrH=NrV. The retrievals were performed by varying Nrp from −1 to 2 by steps of 1 and Hr from 0 to 0.6 by steps of 0.1. At satellite scale, the results show that combining vegetation and roughness effects in a single parameter provides the best results in terms of soil moisture retrievals, as evaluated against the in situ SM data. Even though our retrieval approach was very simplified, as we did not account for pixel heterogeneity, the accuracy we obtained in the SM retrievals was almost systematically better than those of the Level 3 product. Improved results were also obtained in terms of optical depth retrievals. These new results may have key consequences in terms of calibration of roughness effects within the algorithms of the SMOS (ESA) and the SMAP (NASA) space missions.

Optical spectroscopy of a resonant Bragg structure with InGaN/GaN quantum wells

The optical reflectance and transmittance spectra of a periodic InGaN/GaN semiconductor heterostructure with 60 quantum wells are studied at room temperature. The period of the structure was chosen such that, at some angles of incidence of light, the energy of a photon resonantly reflected from the Bragg structure coincides with the excitation energy for quantum-well excitons in quantum wells. The parameters of these excitons are determined by fitting the spectra measured at two different angles of incidence, 30° and 60°. We take into account the resonant exciton transitions in quantum wells as well as the transitions into the continuous spectrum. The radiative decay parameter is determined to be (0.20 ± 0.02) meV.

Simulation of light interference by a biaxial thin film

In this paper, the interference pattern of reflected light from a biaxial anisotropic thin film (with arbitrary orientation of the principal optical axes) is numerically investigated by a double-reflection approach. The pattern for different film thicknesses under illumination of monochromatic and white light with various polarizations in different angles of incidence is obtained. Comparison with isotropic thin films reveals that a kind of modulation (or banding) appears on the interference pattern.

Determination of the Bimetallic Layers’ Film Thicknesses by Phase Detection of SPR Prism Coupler

In this paper, the phase detection method is demonstrated to determine the film thicknesses of bimetallic layers by surface plasmon resonance (SPR) prism coupler. It was proposed and developed by matching the experimental results to the theoretical curves of the phase difference with different angles of incidence. The results of both of the two metallic film thicknesses obtained by our method coincide well with the measurement results of atomic force microscope (AFM) and spectroscopic ellipsometer (SE) measurement. Both theoretical analysis and experimental results indicate that the method proposed is stable and reliable, and feasible to be used to determine the film thickness of bimetallic layers directly with nanometer order resolution.

Removal of all mosaic grating errors in a single-interferometer system by a phase-difference reference window.

An interference method to remove all mosaic grating errors using a phase-difference reference window without compensation for coupled mosaic errors or analyzing the far-field diffraction intensity patterns is proposed. The reference window is achieved by adding a small-aperture prism; therefore, the incident light on the mosaic gratings contains two different angles of incidence and optical paths, eliminating the uncertainty of longitudinal mosaic error in the interferometer. The mathematical model of the method is established and optical arrangement is presented. Interference fringes with the reference window and alignment process are simulated and the accuracy of mosaic errors are analyzed. The experimental and simulation results show that our method can eliminate longitudinal mosaic error and all other mosaic grating errors. The accuracy of angle mosaic errors can be less than 1 μrad and position mosaic errors can be to the nanometer level. Compared with the far-field diffraction intensity patterns method, our method reduces the complexity of the optical structure and ensures measurement accuracy.

Transmission and radiation of acoustic oblique incident through tube arrays based on phononic crystals theory

In a utility boiler, the heat exchanger’s structure is similar to a two-dimensional phononic crystal. Based on the phononic crystal theory, this paper studies sound propagation through tube arrays as a function of the incident sound direction and the surroundings temperature. We carried out both the computational and experimental work for particular values of the pitch and diameters in the tube arrays and studied the band-gap diagram and insertion loss spectra for different angles of incidence. The first band gap is found to correspond to Bragg’s Law while the second band gap moves to lower frequencies as the angle increases. Simulations indicate also that the uneven temperature field influences the insertion loss spectrum. Results of experiments and calculations confirm that, for a particular tube array, the most important factors influencing sound propagation are incidence angle and the surrounding temperature. For the acoustic source in tube arrays, the acoustic radiation have relation with the frequency whether in the acoustic bang gap or not. The results should provide a basis for further work: both on sound source localization and low frequency sonic cleaning in large tube arrays.

Estimating the Solar Transmittance of Urban Trees Using Airborne LiDAR and Radiative Transfer Simulation

This paper presents a method for estimating the solar transmittance of urban trees using airborne light detection and ranging (LiDAR), and the radiative transfer simulation of vegetation. The leaf area density (LAD) distribution of trees with voxel size 1 m × 1 m × 0.5 m is estimated using high-resolution and multireturn airborne LiDAR data. The LAD of voxels having few incident laser beams is corrected from the surrounding voxels. The LAD of the periphery of the crown is discretized into 0.5 m × 0.5 m × 0.5 m voxels to accurately calculate the shaded area. The resulting LAD distribution is used in a radiative transfer simulation to calculate the solar transmittance of the trees. We verified the accuracy of the calculated transmittance by comparing it with empirical data for a Zelkova serrata. The comparisons were conducted under different angles of incidence of laser beams and solar radiation. When the angle between the incident laser beams and solar radiation was small, the transmittance could be accurately estimated. The LAD correction enabled the method to be applied to a broader range of the angle between beams and solar radiation. When the zenith angle of the incident laser beams was small (<; 10°) and the LAD correction was carried out, the errors in transmittance were within 0.06 for solar altitudes greater than 40°. Next, we examined the difference in solar transmittance among streets caused by the layout of trees and buildings and the growth condition of the trees. It was shown that the present method is able to quantify the solar shading provided by urban trees and take into account LAD, tree layout, and the spatial geometry of the surrounding buildings.

Correcting the planar perspective projection in geometric structures applied to forensic facial analysis

The process of forensic facial analysis may be founded on several scientific techniques and imaging modalities, such as digital signal processing, photogrammetry and craniofacial anthropometry. However, one of the main limitations in this analysis is the comparison of images acquired with different angles of incidence. The present study aimed to explore a potential approach for the correction of the planar perspective projection (PPP) in geometric structures traced from the human face. A technique for the correction of the PPP was calibrated within photographs of two geometric structures obtained with angles of incidence distorted in 80°, 60° and 45°. The technique was performed using ImageJ® 1.46r (National Institutes of Health, Bethesda, Maryland). The corrected images were compared with photographs of the same object obtained in 90° (reference). In a second step, the technique was validated in a digital human face created using MakeHuman® 1.0.2 (Free Software Foundation, Massachusetts, EUA) and Blender® 2.75 (Blender® Foundation, Amsterdam, Nederland) software packages. The images registered with angular distortion presented a gradual decrease in height when compared to the reference. The digital technique for the correction of the PPP is a valuable tool for forensic applications using photographic imaging modalities, such as forensic facial analysis.

Experimental Explorations of the Torsional Vortex-Induced Vibrations of a Bridge Deck

AbstractWith the specific objective of exploring the surface pressure characteristics and further revealing the torsional vortex-induced vibration (VIV) mechanisms of a bridge deck with a particular geometry, numerous simultaneous pressure measurement campaigns were performed in a wind tunnel for aerodynamic-countermeasure–modified and unmodified sections of a section model at different angles of incidence under the conditions of smooth or turbulent flow. The mean and fluctuating pressure distributions, instantaneous pressures at typical instants, dominant pressure frequencies, pressure phase differences at the dominant frequency of individual pressure measurement taps, and the correlation coefficients among local and global torsional moments were studied, revealing the origins and mechanisms of torsional VIVs. The results demonstrate that the angle of incidence, flow conditions (smooth or turbulent), and installation of a spoiler exert significant effects on the surface pressure distributions, hence affe...

Reflection and transmission of plane wave through fluid layer of finite width sandwiched between two monoclinic elastic half-spaces

This paper studies the reflection and transmission of a plane wave through a fluid layer of finite width sandwiched between two dissimilar monoclinic elastic half-spaces. Closed-form expressions for the phase velocity of quasi-waves (qP and qSV) have been obtained. The reflection/transmission coefficients and energy divisions have been procured for all the reflected and transmitted waves in terms of phase velocity, propagation vector, elastic constants and width of the layer. It has been noticed that these epitomes depend not only upon the incident angle and width of the layer, but also on the character of incident wave. Energy proportions have been calculated numerically to validate the rule of energy conservation at different angles of incidence. Graphical representation has been performed to demonstrate the analytical findings.

A study of angle dependent surface plasmon polaritons in nano-hole array structures

We report that the light-matter interaction in metallic nano-hole array structures possess a subwavelength hole radius and periodicity. The transmission coefficient for nano-hole array structures was measured for different angles of incidence of light. Each measured transmission spectrum had several peaks due to surface plasmon polaritons. A theory of the transmission coefficient was developed based on the quantum density matrix method. It was found that the location of the surface plasmon polariton and the heights of the spectral peaks were dependent on the angle of incidence of light. Good agreement was observed between the experimental and theoretical results. This property of these structures has opened up new possibilities for sensing applications.

Influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light in biaxial crystals

The influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light have been investigated for biaxial crystals. Analytical expressions for the optical rotation in the direction of optical axis are obtained with allowance for both the symmetric and antisymmetric parts of gyration pseudotensor. The polarization azimuth and transmitted light ellipticity have been calculated at different angles of incidence.

Specific features of optical activity in various uniaxial crystals

The influence of the antisymmetric part of the gyration pseudotensor on the characteristics of reflected and transmitted light has been considered for crystals of classes 3, 4, and 6. The results are compared with the corresponding data for crystals of classes 32, 422, and 622 with a symmetric gyration pseudotensor. Specific features of the optical activity in crystals of classes 3m, 4mm, and 6mm with an antisymmetric gyration pseudotensor have been studied. Crystals of classes \(\bar 42m\) and \(\bar 4\) with the symmetric gyration pseudotensor of an unusual form have been considered. The polarization azimuth and ellipticity of the reflected and transmitted light are calculated for these crystals at different angles of incidence.

Far-field diffraction microscopy at λ/10 resolution

Tomographic diffraction microscopy is a three-dimensional quantitative optical imaging technique in which the sample is numerically reconstructed from tens of holograms recorded under different angles of incidence. We show that combining the measurement of the amplitude, the phase, and the polarization of the field scattered by the sample with an approximate knowledge of the sample permittivity allows reconstruction of spatially complex samples up to 50 nm resolution. This technique should be particularly useful for imaging objects made of known materials.

SU‐F‐T‐442: Dose Distribution Comparison for Post‐Laryngectomy Stoma Area Between Conventional AP and VMAT Plans with Or Without Bolus

Purpose:To compare dose distributions of conventional AP vs. VMAT treatment plans with or without bolus around post‐laryngectomy stoma.Methods:Radiation dose coverage for post‐laryngectomy stoma was analyzed using a set of real‐case CT‐simulation images. After meticulous contouring of the catheter cuff, stoma lumen, peri‐stoma skin and subclinical tumor bed at the larynx, the resulting dosimetry plans were analyzed with or without a 5 mm bolus placement. Wet gauze was used to minimize the effect of any air gap. Four plans were generated: AP superclavicular (SCV) plan with or without bolus, and VMAT plan with or without bolus. A dose of 60Gy in 30 fractions was prescribed at 3 cm depth for AP SCV plan, and to 95% of the PTV volume for VMAT plan.Results:For the conventional AP SCV plan, the peri‐stoma skin dose is sensitive to bolus placement as well as air gap compensation by wetted gauze (V95% of 20.7%, 33.0% and 94.8% for no bolus, bolus without and with air gap compensation, respectively). For stoma lumen, the dose drops off rapidly in depth. The catheter cuff may have certain dose‐buildup effect, but air gap around it and under the bolus placed can pose a more serious problem. The dose distributions of the two VMAT plans are moderately different for peri‐stoma skin (V95% of 95.0% with bolus and air gap compensation, and 82.3% without bolus), but nearly identical for stoma lumen (V95% of 91.5% and 92.0%, respectively). VMAT allows beamlets with different angles of incidence that helped achieve such dose distribution around the stoma even without bolus placement.Conclusion:Overall, the dose coverage around the stoma in the VMAT plan is better than the conventional AP SCV plan. To achieve optimal dose distribution, it is still recommended to place physical bolus and reduce the air gaps.

Design, characterisation and fabrication of a broadband polarisation‐insensitive multi‐layer circuit analogue absorber

A broadband polarisation-independent circuit analogue absorber comprising multi-layer resistive frequency selective surfaces (FSS) has been presented in this study. The proposed structure consists of a periodic arrangement of square loops loaded with lumped resistors and these square loops are printed on dielectric substrates separated by an air spacer. The simulated result shows the reflectivity below -10 dB in the frequency range from 4.96 to 18.22 GHz (fractional bandwidth of 114.40%) under normal incidence, covering C, X, and Ku bands. An equivalent circuit analysis has been introduced to characterise the proposed absorber, which shows good matching with the full-wave analysis. The effects of the individual FSS layers and the air spacer have been studied and several parametric variations have been carried out to examine the sensitivity of the design parameters on the absorption bandwidth. Finally, the designed absorber has been fabricated and measured in anechoic chamber, which shows good agreement between the experimental results and the simulated responses, under different angles of incidence as well as for various polarisation angles.

On the Metasurface-Based Comb Filters

This letter reports a new type of plasmonic metamaterial-based comb filter with the metasurface as similar to the Salusbury window, and comprised of three layers—sub-wavelength-sized periodic gold nanorods surrounded by free-space (i.e., the metasurface), silicon, and silver nanolayers. The structure yields multiple absorption peaks upon impinged by electromagnetic waves. The metasurface behaves as a comb filter—certain spectral frequencies are absorbed and the remaining ones are reflected back. The performance of filter is analyzed in UV, visible, and near infrared (NIR) regimes considering the $p$ - and $s$ -polarized excitations under different angles of incidence.

Ultrasonic Shear Wave Reflection Method for Direct Determination of Porosity and Shear Modulus in Early-Age Cement Paste and Mortar

AbstractAn ultrasonic technique for measuring reflection of horizontally polarized shear (SH) waves at different angles of incidence from early-age hydrating mortar and cement paste is described. Measurements from mortar with varying sand content are presented. A poroelastic formulation for predicting wave reflection from hydrating mortar, which considers mortar as a two-phase, water-filled solid skeleton, is developed. In this representation, the solid phase in early-age hydrating mortar consists of sand, products of hydration and unhydrated cement. Reflection at the mortar interface is predicted using the poroelastic theory. Changes in the reflected amplitude of SH waves are used to obtain changes in the water-filled pore space and the shear modulus of the porous skeleton within the two-phase poroelastic idealization. The water-filled pore space in mortar is identified with the porosity in the two-phase poroelastic material. The porosity of mortar obtained from the poroelastic idealization when referrin...

A probabilistic study of reflection and transmission coefficients of random anisotropic elastic plates

This paper presents a probabilistic framework to analyze wave reflection and transmission through anisotropic elastic plates. The elastic plate is sandwiched between two homogeneous fluids and has randomly varied elastic properties in the through-thickness direction. By introducing a stochastic model for quantitative description of heterogeneous elastic properties in the plate, the effects of material heterogeneity on reflected and transmitted waves may be investigated from a probability point of view. The reflection and transmission coefficients are computed via the semi-analytical finite element (SAFE) method. A sensitivity study is presented, highlighting effects of the uncertainty of elasticity properties on the reflection and transmission coefficients measured from different angles of incidence.

Investigation of the chemical enhancement contribution to SERS using a Kretschmann arrangement

Using a Kretschmann configuration‐based setup, surface‐enhanced Raman scattering (SERS) experiments have been performed on a monolayer of Nile blue. The experiment has been optimized to achieve reproducible conditions. Laser excitation resulted in a fast decay of the Raman line intensities ending at a stable signal level. We have analyzed this intensity variation mode specifically. The Raman deactivation rate was found to be different for different vibrational modes where high‐wavenumber vibrations showed slower decay than the group of low‐wavenumber modes. SERS spectra were obtained excluding the contribution of this deactivation process for different angles of incidence of the exciting laser beam. The variation of the surface plasmon excitation in the thin silver film coated onto the prism surface of the Kretschmann configuration resulted in drastically different relative enhancements of the different Raman modes pointing to a major contribution of the chemical enhancement mechanism in the single‐layer SERS experiment. The enhancement was found to be mode‐specific. High‐wavenumber modes showed a stronger enhancement than the low‐wavenumber group. Copyright © 2016 John Wiley &amp; Sons, Ltd.