Surface Scatter Research Articles

Direct-Path Backscatter Measurements Along the Main Reverberation Track of TREX13

The primary goal of the Target and Reverberation Experiment in spring 2013 (TREX13) was to identify the major physical mechanisms responsible for midfrequency reverberation. While both the sea surface and seafloor can contribute to reverberation, the seafloor is typically dominant in shallow water environments. To determine the level of this contribution at the TREX13 site, the bottom backscatter sonar (BBS) was deployed from a dive boat at multiple locations around the site. The BBS consists of a source and a receiver mounted on a short bracket that is suspended above the seafloor to measure direct-path bottom backscatter at 3 kHz. Data near normal incidence were interpreted as bottom reflectivity, which was used to quantitatively explain the range-dependence of the sediment composition at the experiment site. Two factors restricted the estimates of the bottom backscatter strength to the minimum grazing angle of 21 $^\circ$ : the currents at the experiment site made it difficult to position the system close to the seafloor, and the shallow water depth resulted in sea surface scatter contaminating small angle bottom backscatter. From the measured backscatter strength and by utilizing available environmental data, initial models of scattering strength indicate that at the shallow grazing angles of importance to reverberation, the scattering on the sand ridges is dominated by roughness scattering while in the muddy areas of the ridge swales, volume scattering dominates. The volume scattering from these mud areas is significantly stronger than the roughness scattering on the ridges by as much as 10 dB and may explain the substantial fluctuations observed in the reverberation as a function of range.

Scattering and specular reflection of solar reflector materials – Measurements and method to determine solar weighted specular reflectance

Reflector materials directly affect the performance of concentrating solar applications such as solar thermal power plants or process heat installations. For concentrating collectors the specular reflectance and scattering of reflector materials in the near specular range is of special relevance for a good performance. In this article, we show characteristic bidirectional scatter and specular reflectance curves for solar materials, such as glass-based, polymer-based and aluminum-based reflectors, measured using the instrument VLABS, a commercial reflectometer and a spectrophotometer. The solar weighted specular reflectance is a relevant performance indicator, allowing the comparison of the different reflectors. However, usually it is not measured in solar laboratories. This is why this article presents a method for modelling of solar weighted specular reflectance based on hemispheric reflectance and single wavelength measurements. The model applies surface scatter theory and the concept of total integrated scatter. It allows to predict the specular reflectance for the solar spectral range. The application of the model to solar reflector materials with different surface roughness features and the impact of beam spread on the solar weighted specular reflectance is shown. The methodology allows for an improved evaluation and comparison of innovative reflector materials for solar applications.

Assessing site organization and development using geophysical prospection at Dayatou, Gansu, China

Recent magnetometry survey at the late Neolithic site of Dayatou (大崖头) in the Tao River (洮河) Valley of Gansu Province, China, has revealed a complex, multiperiod habitation site made up of several discrete occupation clusters. While this site was previously interpreted as a large (~140,000 m2), primarily Majiayao (马家窑) period site, our geophysical survey, augering, and targeted excavation results point to the site containing several smaller (~8500 m2) areas of intense occupation separated by magnetically quieter zones in some areas and ditch features in others. The occupations appear to date to varying Majiayao subphases as well as subsequent periods. These results call into question the usefulness of site size rank hierarchies based on surface scatters of pottery alone, which are commonly used in studies of early complexity in China. This study demonstrates the usefulness of geophysical survey combined with targeted excavation for understanding the complex development processes at work in the formation of late Neolithic and early Bronze Age sites in northern China.

Scattering-Induced Absorption Acts as a Cancer Treatment Monitor

Uncontrolled growth of ovarian cancer cells is the fifth leading cause of female cancer deaths. Here, we describe the role of scattering-induced absorption in monitoring the cancer treatment efficiency in real-time. We measure the optical interaction between the evanescent fields of microfiber and ovarian cancer inter-cellular medium at different treatment stages. By introducing the roughness of silica glass, we demonstrate that the treatment of tumor cells with GDC0032, a beta-sparing PI3K, induces both cells growth arrest and alter the spectral lines in a dose-dependent manner. The data support observed affected tumor cells with decrease in proliferation and their spatial distribution. Spectral absorption signatures are correlated with optical micrographs and western blot tests. These observations are mediated by surface scatterers out of silica glass material, form an essential step toward the development of early detection of response to cancer therapy.

Time-Varying Ocean-Like Surface Scattering at Grazing Incidence: Numerical Analysis of Doppler Spectrum at HF/VHF/UHF Bands

This paper numerically analyzes the characteristics of the Doppler spectrum at HF/VHF/UHF bands from 1D time-varying ocean-like surfaces at grazing incidence in vertical polarization mode. The rough surface is transformed into a local perturbation plane which has its roughness flattened at the edges. The scattering waves include coherent reflected wave and incoherent scattering waves. The surface currents exciting the incoherent scattering waves are regarded as the unknowns which can be solved from the improved surface integral equation using the method of moments (MoM). The incident plane wave allows the incident angle to reach up to 90° (grazing incidence). Then the backscattering wave in the far field can be calculated, and the Doppler spectrum is obtained by coherent Monte-Carlo simulation. Firstly, the validity of the method is verified by comparing with the mature small perturbation method at the HF band. Then the incident wave frequency is asymptotically increased from HF to UHF, and the application range of the SPM is quantitatively evaluated in the Doppler spectrum domain. Finally, the paper focuses on analyzing the characteristics of Doppler spectrum in different bands and different sea states and comparing the influence of nonlinear ocean waves on the Doppler spectrum at different frequencies.

Temporal Change of Seismic Earth's Inner Core Phases: Inner Core Differential Rotation or Temporal Change of Inner Core Surface?

AbstractWe discuss the question whether inner core (IC) differential rotation or temporal change of the IC surface provides a consistent interpretation for temporal changes of the IC‐related phases and their coda. While temporal change of the IC surface is required and provides a consistent explanation to all the seismic observations, we present three lines of seismic evidence showing that IC differential rotation cannot provide a consistent or reasonable interpretation for the observed temporal change of seismic waves from repeating earthquakes in the South Sandwich Islands (SSI) and the Middle America subduction zone. (1) Changed PKIKP/PKiKP coda between events in a doublet in SSI indicates an IC surface scatterer that simply disappeared, with no associated energy in the later event for any assumed IC differential rotation. (2) Within a cluster in SSI, comparisons between temporal changes of PKIKP wave and its coda of the earlier and later event pairs yield contradictory estimates of differential rotation rate change by a factor of at least 27, using different portions of seismic data. (3) The seismic data from repeating earthquakes in Middle America indicate a PKiKP temporal change of 0.017–0.04 s on a timescale of 8–85 days, requiring an unreasonable rotation rate of at least 8.6°/year. We conclude that the observed temporal changes of IC phases are caused by temporal changes of the IC surface, which occur in some localized regions within a timescale of days or months, a phenomenon that should provide important clues to our understanding of core dynamics.

Simulation of Oscillatory Scattered Ion Yields in He+-Metal Surface Scattering Including the Coulomb Repulsive Interaction

The effect of the intra-atomic Coulomb repulsive interaction, U, between different electrons in He atoms on the ion survival probability (ISP) is calculated with the mean-field (Hartree–Fock) appro...

Effects and Characterizations of Pulse Electrodeposition Parameters of Silver on Surface Roughness and Scattering Parameters of Horn Antennas

Electronic conductivity is a parameter that exhibits the free-electron transportation ability of a material. The radiation efficiency of reflector type antennas and insertion loss of waveguide transmission lines are directly related to the conductivity of the materials used to construct such structures. Signal quality of antenna and waveguides in the transmission of electromagnetic waves are also very much dependent on the surface finish that has good conductivity [1]. The use of pulse currents produces homogenous deposits of better surface finish than direct current [2,3]. Effects of pulse parameters on the surface properties of silver coatings of the copper base material have been analyzed in terms of surface roughness and S-parameter (scattering parameter). Grain morphologies of silver coatings were characterized by SEM and XRD. The duty cycle, frequency and the average current density were selected as three pulse parameters. Three levels were selected for each parameter in the experimental design. A relationship was developed for surface finish in terms of duty cycle, average current density and pulse frequency. The S11 scattering parameter observations were made relative to a gold-plated reference coupon. It was analyzed that smoother surfaces had more reflection power in terms of S11 parameter thus decreasing the loss of radiation. Therefore, the results may be used to develop a silver coating procedure to improve signal quality of antenna and waveguides in the transmission of electromagnetic waves. [1] Balanis, C. A. (1989), “Advanced Engineering Electromagnetics”, John Wiley & Sons [2] Chandrasekar, M.S. and Pushpavanam, M. (2008) ‘Pulse and pulse reverse plating—Conceptual, advantages and applications’, Electrochimica Acta, 53(8), pp. 3313–3322. [3] Arslan, B., Demirci, G., Karakaya, İ. and Erdoğan, M. (2015) ‘Formation of gold-plated electroformed copper structures’, Advances in Materials and Processing Technologies, 1(3-4), pp. 384–393.

Self-Induction of a Fine Cylindrical Metallic Wire Versus a Mechanism of Electron Surface Scattering

The self-induction of a thin cylindrical metallic wire has been calculated. A general case when the ratio of the electron free path to the wire radius may take an arbitrary value has been considered. The dependence of the regular reflectance on surface defect density and angle of incidence of electrons on the wire’s inner surface has been taken for boundary conditions of the problem.

Electromagnetic Scattering of Rough Ground Surface Covered by Multilayers Vegetation

A microwave scattering model is proposed for the ground surface covered with multilayers vegetation. The vegetation leaves are simulated with the discrete elliptical particles in layers, which are randomly distributed above the randomly rough surface. The finite element method is applied to solve the scattering magnetic field equation based on the Dirichlet boundary, and the relationship between the radar cross section and bidirectional reflectance distribution function is deduced with the coherent scattering field. The internal mechanism of microwave scattering of multilayers vegetation is explored with the numerical results, and the relationship of vegetation growing parameter with scattering characteristic is established.

The distribution, composition, and particle properties of Mars mesospheric aerosols: An analysis of CRISM visible/near-IR limb spectra with context from near-coincident MCS and MARCI observations

The Compact Reconnaissance Imaging Spectral Mapper (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) obtains pole-to-pole observations (i.e., full MRO orbits) of vertical profiles for visible/near-IR spectra (λ= 0.4–4.0 μm), which are ideally suited to identifying the composition and particle sizes of Mars ice and dust aerosols over 50–100 km altitudes in the Mars mesosphere. Within the coverage limitations of the CRISM limb data set, a distinct compositional dichotomy is found in Mars mesospheric ice aerosols. CO2 ice clouds appear during the aphelion period of Mars orbit (Solar Longitudes, Ls ∼ 0–160°) at low latitudes (∼20S–10N) over specific longitude regions (Meridiani, Valles Marineris) and at typical altitudes of 55–75 km. Apart from faint water ice hazes below 55 km, mesospheric H2O ice clouds are primarily restricted to the perihelion orbital range (Ls∼160 – 350°) at northern and southern mid-to-low latitudes with less apparent longitudinal dependences. Mars mesospheric CO2 clouds are presented in CRISM spectra with a surprisingly large range of particle sizes (cross section weighted radii, Reff = 0.3 to 2.2 μm). The smaller particle sizes (Reff ≤1 μm) appear concentrated near the spatial (latitude and altitude) boundaries of their global occurrences. CRISM spectra of mesospheric CO2 clouds also show evidence of iridescence, indicating very narrow particle size distributions (effective variance, Veff ∼ 0.03) and so very abrupt CO2 cloud nucleation. Furthermore, these clouds are sometimes accompanied by altitude coincident peaks in 1.27 μm O2 dayglow, which indicates very dry, cold regions of formation. Mesospheric water ice clouds generally exhibit small particle sizes (Reff = 0.1–0.3 μm), although larger particle sizes (Reff = 0.4–0.7 μm) appear infrequently. On average, water ice cloud particle sizes decrease with altitude over 50–80 km in the perihelion mesosphere. Water ice mass appears similar in clouds over a large range of observed cloud particle sizes, with particle number densities increasing to ∼10 cm−3 for Reff = 0.2 μm. Near coincident Mars Climate Sounder (MCS) temperature and aerosol profile measurements for a subset of CRISM mesospheric aerosol measurements indicate near saturation (H2O and CO2) conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading. Dayside (3 pm) mesospheric CO2 clouds with larger particle sizes (Reff ≥0.5 μm) scatter surface infrared emission in MCS limb infrared radiances, as well as solar irradiance in the MCS solar band channel. Scattering of surface infrared emission is most strikingly presented in nighttime (3 am) MCS observations at 55–60 km altitudes, indicating extensive mesospheric nighttime CO2 clouds with considerably larger particle sizes (Reff∼7 μm). Mesospheric CO2 ice clouds present cirrus-like waveforms over extensive latitude and longitude regions (10°×10°), as revealed in coincident Mars Color Imager (MARCI) nadir imaging. Solar tides, gravity waves, and the large orbital variation of the extended thermal structure of the Mars atmosphere influence all of these behaviors. Mesospheric dust aerosols appear infrequently over the non-global (planet encircling) dust storm era of the CRISM limb data set (2009–2016), and exhibit smaller particle sizes (Reff = 0.2–0.7 μm) relative to dust in the lower atmosphere. One isolated case of an aphelion (Ls = 96°) mesospheric dust layer with large dust particle sizes (Reff ∼2 μm) over Syria Planum may reflect high altitude, non-local transport of dust over elevated regions.

Employing constant photocurrent method for the study of defects in silicon thin films

Different optical characterization techniques have been performed on a series of microcrystalline silicon thin films deposited using very high-frequency-assisted plasma-enhanced chemical vapor deposition process. The constant photocurrent method has been employed to study the defects states in density of states spectra of hydrogenated microcrystalline silicon thin films. The photocurrent measurements demonstrate anisotropy in the optoelectronic properties of the material. We have analyzed the optical absorption coefficient from UV spectroscopy and with the help of constant photocurrent method. The spectra have been analyzed in broad region and are presented for both the cases, i.e., surface and bulk light scatterings. The spectra were interpreted in terms of disorder, resulting defect density, crystalline/amorphous volume fractions and material morphology. The subgap-related parameters such as absorption coefficient, characteristic energy E0 of tail states and density of subgap defect states together with an estimate of the bandgap of silicon films prepared at various crystalline fractions have also been estimated. The density of localized tail states is found to fall exponentially toward the gap with band tail width of about 110 meV.

Phenomenological modelling of light transmission through nanowires arrays

A phenomenological model has been developed and discussed. The model is able to describe the experimentally measured light transmission of nanowires arrays. Two representative samples were studied in this report. A well aligned nanowires sample was first modelled by an effective layer model with surface roughness added. Then a slightly tilted nanowires sample with round top was phenomenologically modelled by a two layers model with a first top layer of an effective medium which includes a volume scattering contribution (Mie theory). Roughness and waviness are added to account for the nanowires small and large scale fluctuation in height. This phenomenological description was proven to be feasible by fitting experimental data. As a conclusion, light transmitted through randomly distributed nanowires can be explained by the combination of volume and surface scatterings using respectively Mie theory and rough Fresnel coefficients at the interfaces.

Ultrashort pulse-induced elastodynamics in polycrystalline materials. Part I: Model validation

The coupled thermal-mechanical response of a polycrystalline metallic film in response to ultrafast optical impingement is investigated. The thermo-elastodynamics formulated in the article considers laser absorption along the axial direction and thermal diffusion along the radial direction to account for the normal and shear stresses initiated by the rapid heating. The generalized formulation incorporates a two-step hyperbolic temperature model that characterizes the energy transport of electrons and lattices as finite in velocity. The coupling of thermal and mechanical fields is established through considering the energy dissipated in the form of propagating thermo-mechanical disturbances. The thermo-elastodynamical response of the polycrystalline film is found to be a strong function of the electron heat capacity that is also temperature-dependent. In addition, grain size effects due to film surface and grain-boundary scatterings are found to impact several thermophysical properties of the material. The impact of the energy transport of electrons is particularly prominent when the thickness becomes comparable with the electron mean-free-path. A staggered-grid finite difference scheme is followed to simultaneously resolve the coupled thermo-elastodynamical responses using an axisymmetric model. The time variation of the normalized electron temperature of a single crystalline gold film derived from the generalized model is favorably examined against published physical data, thus demonstrating the feasibility of the formulation in depicting the electron transport dynamics in response to non-ablating ultrafast irradiation.

Three Dimensional Image-Based Radar Cross Section Extrapolation via Planar Projective Transforms

Conventional radar cross section (RCS) measurements require far-field or compact-antenna-test-range (CATR) conditions, which have strict restrictions and high implementation costs. By contrast, RCS extrapolation methods in the near zone are more convenient and practical, which become the research emphasis in recent years. This paper presents a novel RCS extrapolation method based on the combination of near-field 3D synthetic aperture radar (SAR) technique and planar projective transforms (PPT) algorithm. Firstly, to extract the target’s reflectivity distribution, we apply near-field 3D SAR imaging and obtain 3D near-field RCS (NFRCS) images. Secondly, to meet the requirement of RCS measurements, we derive a novel correction factor used to precisely expand 3D NFRCS images. Finally, we extrapolate the plane-wave responses in the azimuth-vertical dimensions, which presents as planar patterns. The proposed method utilizes the complete 3D image-based information to overcome the inherent constraints of classical RCS extrapolation methods on application scenarios, which has the advantages of broad applicability and high flexibility. The detailed derivation and implementation of this method are described in this paper. The simulation and experiment results verify that the proposed method can provide the equivalent CATR result within ±11° azimuth and elevation angles, and it is applicable to precisely measuring the point, surface, and complex scatterers.

X射线散射法测量Wolter-I型掠入射望远镜的表面粗糙度

The X-ray scattering method is investigated in application of characterizing surface roughness of X-ray grazing incidence telescope. The surface figure effect on the scattering diagram of the curved rough mirror is analyzed in detail based on generalized Harvey-Shack surface scatter theory and image formation theory, when smooth-surface approximation is met and the width of the incident beam is about one tenth of spatial wavelength of the surface figure. Based on the analysis, the characterizing scheme is designed and the determination error of the one-dimensional power spectral density function due to the finite width of the receiving slit before the detector is discussed. The scheme is simulated with Zemax and the simulated results verify that the surface figure only affects the measuring accuracy of the low-spatial-frequency surface roughness. The method overcomes difficulty in measuring roughness of the grazing incidence mirror with high resolution conveniently during the development of the X-ray grazing incidence telescope.

The effects of heavy-duty machinery on the formation of pseudo-knapping debitage in Stone Age cultural landscapes

Abstract

Evidence of Neolithic settlement in the foothills of the Western al‐Hajar Mountains

AbstractSystematic prospection and excavations in the Rustaq region of northern Oman, approximately 45 km from the coast in the foothills of the Western Hajar Mountains, have revealed an unexpectedly dense record of Neolithic sites. Besides surface scatters of lithic artefacts, excavation at the site of Hayy al‐Sarh recovered two stratified archaeological horizons (AHs). The upper horizon, AH I, contained pierced marine shells that provided an age of the archaeological material of about 6800 to 7500 years cal BP. Typologically the AH I lithic assemblage compares to the Suwayh facies defined at the coast 300 km to the east. Whether the marine shells and cultural affinities point towards exchange with coastal communities or possibly seasonal movement remains an open question at this state of research, but this new evidence for inland Neolithic settlement near Rustaq provides important new data that will help improve our understanding of spatial patterns of Neolithic demographic variability.

Akhiezer mechanism limits coherent heat conduction in phononic crystals

Heat in phononic crystals (PnCs) is carried by phonons, which can behave coherently (wave-like) or incoherently (particle-like) depending on the modes, temperature, and length scales. By comparing the measured thermal conductivity of PnCs with theories, recent works suggest that thermal conductivity of PnCs can be explained by considering only surface and boundary scatterings, which not only backscatter phonons but also break their coherence. The logic here is that since average phonon wavelength at room temperature is only a few nanometers, the roughness at the surfaces and boundaries make the scattering diffusive (break the phase coherence of phonons), and thus only very long wavelength (low frequency) phonons with negligible contribution to total thermal conductivity remain coherent. Here, we theoretically show that in a thin film PnCs, the low frequency coherent phonons could significantly contribute to thermal conductivity when assuming the three-phonon scattering model for intrinsic scattering because of their extremely large density of states that result from the low dimensional nature. Yet, further analysis shows the contribution of the low frequency coherent phonons is still negligible within temperature range from 130 to 300 K due to the Akhiezer mechanism, which properly answers the question why the thermal conductivity of PnCs can be explained by considering only scattering of incoherent phonons at these temperatures.

First-order nonparaxial scalar theory of surface and bulk scattering for high-quality optical coatings.

A novel nonparaxial scalar theory is presented to calculate the angular scattering that is due to interface roughnesses or bulk inhomogeneities in a high-quality optical coating. Based on the empirically modified Beckmann-Kirchhoff surface scatter model, this theory in surface scattering and bulk scattering predicts similar formulas for the angular scattered intensity, and at the same time provides new understanding and insight into multilayer scattering phenomena. It is worth noting that the derived expressions are in the same form as those given by the typical vector methods. Based on comparisons of the surface and bulk models with the corresponding typical models for several multilayer designs, the novel theory is demonstrated to be valid for multilayer coatings even with large incident and scattering angles.