Roughness Spectrum Research Articles

Ripples in amorphous chalcogenide films under homogeneous laser illumination

Under homogeneous illumination of thin chalcogenide glass films by polarized light at a wavelength near the band gap ripples form, with a period of the order of 10–15µm, directed normal to the light polarization. The formation of the ripples cannot be explained by interference phenomena, which predict the ripple periods of the order of light wavelength. Our experimental and theoretical studies of the ripple formation in 1µm thick As10Se90 chalcogenide films show that the profile variation occurs due to lateral mass transport accelerated by light. The ripple formation is caused by competition between capillary forces and steady state electrostatic forces induced by redistribution of electrons and holes generated by light. Under these driving forces, each harmonic of the film roughness spectrum should exponentially grow or flatten, depending on its frequency. The average period of the ripples corresponds to those harmonics in the roughness spectra, which grow with maximum rate. Light-induced diffusion coefficients have been estimated from the kinetics of the ripple formation.

A full-field perturbation approach to scattering and reverberation in range-dependent environments with rough interfaces.

A perturbation approach to roughness scattering and reverberation in range-dependent environments is developed treating each interface as a superposition of a smooth reference interface, which may include large-scale deterministic features (such as bathymetry changes), and small compared to the acoustic wavelength vertical deviations from this interface that are considered as random roughness perturbations. The reference interface is assumed to be smooth enough to allow analytic or numerical solution for the field in the vicinity of this interface that can then be used in perturbation theory. Expressions for both the reverberation field and average reverberation intensity in a general case of an arbitrary number of rough interfaces are obtained in a form convenient for numerical simulations. In the case of long-range ocean reverberation, several approximations for these expressions are developed, relevant to various environmental scenarios and different types of interfaces: sea-surface, water-sediment interface, buried sediment interfaces, and bottom basement. The results are presented in a simple form and provide a direct relationship of the reverberation intensity with three critical characteristics defined at each interface: (1) local spectrum of roughness, (2) local contrast of acoustic parameters, and (3) two-way full-field transmission intensity calculated taking into account only large-scale changes of the environment.

A COMPARISON OF UAV AND TLS DATA FOR SOIL ROUGHNESS ASSESSMENT

Abstract. Soil roughness represents fine-scale surface geometry which figures in many geophysical models. While static photogrammetric techniques (terrestrial images and laser scanning) have been recently proposed as a new source for deriving roughness heights, there is still need to overcome acquisition scale and viewing geometry issues. By contrast to the static techniques, images taken from unmanned aerial vehicles (UAV) can maintain near-nadir looking geometry over scales of several agricultural fields. This paper presents a pilot study on high-resolution, soil roughness reconstruction and assessment from UAV images over an agricultural plot. As a reference method, terrestrial laser scanning (TLS) was applied on a 10 m x 1.5 m subplot. The UAV images were self-calibrated and oriented within a bundle adjustment, and processed further up to a dense-matched digital surface model (DSM). The analysis of the UAV- and TLS-DSMs were performed in the spatial domain based on the surface autocorrelation function and the correlation length, and in the frequency domain based on the roughness spectrum and the surface fractal dimension (spectral slope). The TLS- and UAV-DSM differences were found to be under ±1 cm, while the UAV DSM showed a systematic pattern below this scale, which was explained by weakly tied sub-blocks of the bundle block. The results also confirmed that the existing TLS methods leads to roughness assessment up to 5 mm resolution. However, for our UAV data, this was not possible to achieve, though it was shown that for spatial scales of 12 cm and larger, both methods appear to be usable. Additionally, this paper suggests a method to propagate measurement errors to the correlation length.

A COMPARISON OF UAV AND TLS DATA FOR SOIL ROUGHNESS ASSESSMENT

Soil roughness represents fine-scale surface geometry which figures in many geophysical models. While static photogrammetric techniques (terrestrial images and laser scanning) have been recently proposed as a new source for deriving roughness heights, there is still need to overcome acquisition scale and viewing geometry issues. By contrast to the static techniques, images taken from unmanned aerial vehicles (UAV) can maintain near-nadir looking geometry over scales of several agricultural fields. This paper presents a pilot study on high-resolution, soil roughness reconstruction and assessment from UAV images over an agricultural plot. As a reference method, terrestrial laser scanning (TLS) was applied on a 10 m x 1.5 m subplot. The UAV images were self-calibrated and oriented within a bundle adjustment, and processed further up to a dense-matched digital surface model (DSM). The analysis of the UAV- and TLS-DSMs were performed in the spatial domain based on the surface autocorrelation function and the correlation length, and in the frequency domain based on the roughness spectrum and the surface fractal dimension (spectral slope). The TLS- and UAV-DSM differences were found to be under ±1 cm, while the UAV DSM showed a systematic pattern below this scale, which was explained by weakly tied sub-blocks of the bundle block. The results also confirmed that the existing TLS methods leads to roughness assessment up to 5 mm resolution. However, for our UAV data, this was not possible to achieve, though it was shown that for spatial scales of 12 cm and larger, both methods appear to be usable. Additionally, this paper suggests a method to propagate measurement errors to the correlation length.

Roughness, resistance, and dispersion: Relationships in small streams

AbstractAlthough relationships between roughness, flow, and transport processes in rivers and streams have been investigated for several decades, the prediction of flow resistance and longitudinal dispersion in small streams is still challenging. Major uncertainties in existing approaches for quantifying flow resistance and longitudinal dispersion at the reach scale arise from limitations in the characterization of riverbed roughness. In this study, we characterized the riverbed roughness in small moderate‐gradient streams (0.1–0.5% bed slope) and investigated its effects on flow resistance and dispersion. We analyzed high‐resolution transect‐based measurements of stream depth and width, which resolved the complete roughness spectrum with scales ranging from the micro to the reach scale. Independently measured flow resistance and dispersion coefficients were mainly affected by roughness at spatial scales between the median grain size and the stream width, i.e., by roughness between the micro‐ and the mesoscale. We also compared our flow resistance measurements with calculations using various flow resistance equations. Flow resistance in our study streams was well approximated by the equations that were developed for high gradient streams (>1%) and it was overestimated by approaches developed for sand‐bed streams with a smooth riverbed or ripple bed.

Viscoelastic rough contact mechanics: A multiscale investigation

The full understanding of the viscoelastic contact mechanics between rough surfaces is a crucial issue in modern engineering research. This paper investigates the role that the number of rough scales, i.e. the cut-off of the power spectrum of the surface roughness, has on quantities like contact area, mean separation, and friction. Furthermore, an effective, though approximate, definition of an equivalent modulus is provided in order to reduce the viscoelastic contact domain to an elastic equivalent one.

Electromagnetic scattering and Doppler spectrum simulation of time-varying oil-covered nonlinear sea surface

Based on the model of Lombardini et al. [J. Atmos. Ocean. Technol.6(6), 882–890 (1989)], which can predict the hydrodynamic damping of rough sea surfaces in the presence of oil films, the influence of sea slicks on the sea surface roughness spectrum and sea surface geometrical structure is examined briefly in the present study. On this basis, the influence of sea slicks on the angular distribution of the bistatic scattering coefficient of sea surfaces and the Doppler spectrum signature of backscattered radar sea-echo is investigated in detail based on a frequency-domain numerical method of the parallel fast multiple method. Simulation results show that Doppler spectrum signatures including Doppler shift and spectral bandwidth of radar sea-echo are significantly affected by sea slicks, which are qualitatively consistent with wave-tank or open sea measurements. Moreover, simulation results indicate that the Doppler spectrum signature is a promising technique for remote sensing of oil films floating on sea surfaces.

General Theory for Pulse Voltammetric Techniques on Rough and Finite Fractal Electrodes for Reversible Redox System with Unequal Diffusivities

The prediction of voltammetric response from the microscopic information of the electrode surface morphology is an important problem of fourth generation electrochemistry which we have theoretically addressed here. We develop a theory for pulse based voltammetric response of reversible charge transfer process with unequal diffusivities on randomly rough electrode. The microscopic information of the electrode surface is incorporated into the response expression in the form of power spectrum of roughness. An elegant expression for the statistically averaged generalized pulse voltammetric current is obtained in terms of single potential step current at rough electrode from which, the explicit current expressions for differential pulse (DPV), staircase (SCV), cyclic staircase (CSCV) and square wave (SWV) voltammetries are obtained for random and finite fractal roughness electrode. The SCV and CSCV responses, as elaborately discussed in our previous work, here we have focused more on the explorations of DPV and SWV responses. In the presence of equal diffusion coefficients of the electroactive species, roughness induces enhancement in the peak heights with retention of peak position at the same potential for DPV as well as SWV. This points towards an enhanced sensitivity of these differential techniques at rough electrodes. In the presence of unequal diffusivities of redox species, SWV shows a distinguished signature of roughness due to variation in peak heights along with alteration in the position of the peaks. Square wave voltammetry on rough electrode shows an asymmetric suppression in the peak height of the anodic or cathodic sampled current plots due to unequal diffusivities which resembles the behavior of a chemically irreversible system.

3D-MID manufacturing via laser direct structuring with nanosecond laser pulses

Abstract 3D molded interconnect device (3D-MID) is a kind of injection-molded thermoplastic part with integrated electronic circuit traces. Currently, it is a hotspot of the electronic and telecommunication equipment industry. Laser direct structuring (LDS) is the main approach to fabricate 3D-MID. Laser scans and activates the surface of thermoplastic parts. After plating, the activated area is coated with copper. In this study, a model was built to describe the mechanisms of interaction between a substrate and laser. The nanosecond laser was applied in the LDS process to manufacture 3D circuit on 3D-MID. With the aid of variable laser pulse width, the model was confirmed by a series of experiments including investigations of roughness, surface structure and energy spectrum. Finally, critical factors affecting the LDS process were found out. They are effective guides for many LDS applications.

夏用および冬用紳士服地の摩擦変動曲線と表面粗さ曲線の相関解析

In this paper, fabric friction curve measured by KES-FB4 surface tester is investigated based on spectrum analysis. Friction spectrum is analyzed compared to surface roughness spectrum obtained simultaneously along the same direction. Samples used are 25 kinds of men’s suitings made of wool including summer and winter use. Results are obtained as follows. (1) Surface roughness of fabrics is divided into “rough” and “smooth” surface of which threshold is 4-5 μm for SMD and -7 for log Pmax, where Pmax is peak value of surface spectrum. (2) The behavior of friction spectrum is divided into three types as follows, (a) uneven surface type, (b) stick-slip (SS) type and (c) mixed type. (3) For the uneven surface type, wave number (1/cm) where the peak value of friction spectrum appears is the same as that of surface roughness spectrum. (4) For the SS type, wave number where the peak value of friction spectrum appears is 20, 40 (1/cm) and low frequency around 0, and does not coincide with that of surface roughness spectrum. (5) For the mixed type, both behaviors of uneven and SS types appear in friction spectrum. (6) The energy of friction spectrum is divided into two parts, i.e. component arised from uneven surface and component arised from stick-slip behavior.

SCATTERING AND TRANSMISSION OF WAVES IN MULTIPLE RANDOM ROUGH SURFACES: ENERGY CONSERVATION STUDIES WITH THE SECOND ORDER SMALL PERTURBATION METHOD

Energy conservation is an important consideration in wave scattering and transmission from random rough surfaces and is particularly important in passive microwave remote sensing. In this paper, we study energy conservation in scattering from layered random rough surfaces using the second order small perturbation method (SPM2). SPM2 includes both first order incoherent scattering and a second order correction to the coherent fields. They are combined to compute the total reflected and transmitted powers, as a sum of integrations over wavenumber kx, in which each integration includes the surface power spectra of a rough interface weighted by an emission kernel function (assuming the roughness of each interface is uncorrelated). We calculate the corresponding kernel functions which are the power spectral densities for one-dimensional (1D) surfaces in 2D scattering problems and examine numerical results for the cases of 2 rough interfaces and 51 rough interfaces. Because it is known that the SPM when evaluated to second order conserves energy, and it can be applied to second order for arbitrary surface power spectra, energy conservation can be shown to be satisfied for each value of kx in the kernel functions. The numerical examples show that energy conservation is obeyed for any dielectric contrast, any layer configuration and interface, and arbitrary roughness spectra. The values of reflected or transmitted powers predicted, however, are accurate only to second order in small surface roughness.

Adhesion of rigid rough contacts with bounded distribution of heights

We develop a “Bradley” (rigid) model for a rough surface with bounded or non-bounded distribution of heights. We observe a large effect of the distribution of heights: for example, for Weibull distributions, the decay from the theoretical strength becomes an inverse power law with the roughness amplitude normalized by the adhesion interaction distance. For Gaussian surfaces which are in principle unbounded distributions, only weak dependence is found on the details of the roughness spectrum. If the truncation comes from a natural process like wear where the height distribution is squashed at a certain truncation level, the latter factor dominates.

Metocean Comparisons of Jason-2 and AltiKa—A Method to Develop a New Wind Speed Algorithm

As well as range, the AltiKa altimeter provides estimates of wave height, Hs and normalized backscatter, σ0, that need to be assessed prior to statistics based on them being included in climate databases. An analysis of crossovers with the Jason-2 altimeter shows AltiKa Hs values to be biased high by only ˜0.05m, with a standard deviation (s.d.) of ˜0.1m for seven-point averages. AltiKa's σ0 values are 2.5–3 dB less than those from Jason-2, with a s.d. of ˜0.3 dB, with these relatively large mismatches to be expected as AltiKa measures a different part of the spectrum of sea surface roughness. A new wind speed algorithm is developed through matching a histogram of σ0 values to that for Jason-2 wind speeds. The algorithm is robust to the use of short durations of data, with a consistency at roughly the 0.1 m/s level. Incorporation of Hs as a secondary input reduces the assessed error at crossovers from 0.82 m/s to 0.71 m/s. A comparison across all altimeter frequencies used to date demonstrates that the lowest wind speeds preferentially develop the shortest scales of roughness.

Measurements and modeling of the variability in normally incident reflections from the seabed

Normal incidence reflection measurements taken during the TREX13 experiment off the coast of Florida show substantial variability. One likely source of variability is due to scattering from the rough surface of the seabed. These data were taken from an omnidirectional source at a relatively low frequency (around 3 kHz). Systems being considered for measuring seabed properties (such as sound speed, density, and roughness) may use commercial echo-sounders that are directional and operate at much higher frequencies. Measurements from the TREX13 data as well as higher frequency systems are analyzed together with modeling to determine how surface roughness effects these measurements. The modeling uses an integral equation approach with a power law roughness spectrum to calculate backscattering of incident plane waves. The effects of changing the model parameters such as seabed type and roughness on the nature of backscattering are examined. The simulated results are compared with the measurements obtained from the experiments. The measurements are further used to calculate the statistical parameters to understand the nature of the normal reflection from a rough seabed.

Reverberation modeling approximately accounting for three-dimensional forward scattering effects

A transport theory approach has been developed for modeling shallow water propagation and reverberation at mid-frequencies with emphasis at 1–3 kHz. With this approach, sea surface forward scattering can be taken into account in a 2-D (range-depth) approximation. While the effects of surface forward scattering on transmission loss are found to be modest (1–2 dB), the corresponding effects on reverberation level for typical conditions can be significant (~10 dB), even though bottom backscatter dominates reverberation in shallow water. An attempt to make data/model comparisons brought out the issue of the proper way of using the 2-D (in horizontal plane) surface roughness spectrum to model forward scattering with a 2-D (range-depth) propagation model. For reverberation modeling, we are investigating the approximation of preserving the distribution in vertical scattering angles in reducing the full 3-D problem to a 2-D (range-depth) problem when using the traditional N ' 2-D approach. A description of the method will be given, followed by data-model comparisons for TREX-13. [Work supported by ONR Ocean Acoustics.]

Microstructure and optical properties of Cu@Ni nanoparticles embedded in a-C:H

Cu@Ni core-shell nanoparticles on a-C:H thin film were prepared by co-deposition of RF-sputtering and RF-PECVD. Samples having different Cu nanoparticle sizes were grown and then Ni layers of different thicknesses were grown over these Cu nanoparticles. Atomic force microscopy indicated that the thin film consisted of nanoparticles 6–14 nm in size. Also, in the present work the RMS roughness and PSD spectra computed from atomic force microscopy (AFM) data were used for studying the morphology of thin films. X-ray diffraction (XRD) profiles show that the Cu nanocrystal core and Ni nanocrystal shell have formed in the film and that the surfaces of these core-shells oxidize when exposed to air. The surface plasmon resonance peak of the Cu nanoparticles can be observed at about 600 nm in a region damped by the increased thickness of the Ni layer. Absorbance in the near-IR region increased as the thickness of the Ni layer increased. The edge of strong absorption observed near the IR region varied with the thickness of the Ni layer.

Statistical linearization on 2 DOFs hydropneumatic suspension with asymmetric non-linear stiffness

Most references on hydropneumatic suspension analysis regard it as harden Duffing spring and take the white noise as the system input, which is quite different from real physical model. It will introduce considerable errors to the analytical result compared with the numerical simulation which makes it impossible to give a good depiction of the hydropneumatic suspension dynamics. In this paper, the dynamic response of the hydropneumatic suspension is worked out using statistical linearization based on 2 DOFs nonlinear suspension model. The damping of the suspension and the tire stiffness are both regarded as linear components and the real road roughness spectrum is used to work out the system input. The explicit analytical equivalent stiffness, dynamic mean value offset from statistic equilibrium position and the sprung acceleration varied with parameters of hydropneumatic spring, road roughness and vehicle velocity are worked out by substituting the nonlinear stiffness of hydropneumatic spring with its first three terms Tyler series at the static equilibrium position using James formula. The comparison of the numerical simulation and analytical result both on statistical parameters and distribution shows the validity of the analysis. The explicit form provides a concise and valid method on hydropneumatic suspension design and optimization.

High-frequency broadband seafloor backscatter in a sandy estuarine environment

Seafloor backscatter collected with high-frequency (>100 kHz) hydrographic echosounders has become an important aspect of seafloor characterization for benthic ecologists and other scientists. The mechanisms that control acoustic scattering at these high frequencies are not completely understood, although surficial roughness and the presence of large scatterers (e.g., shell hash) are likely contributors. To further our understanding of these mechanisms, broadband (100–250 kHz) acoustic measurements were taken at a grazing angle of 45 degrees in a shallow-water, sandy environment with a known presence of shell hash. Stereo imagery was collected simultaneously to quantify the roughness spectrum of the seafloor. Sediment samples were also collected on site of the experiment to quantitatively analyze the content of shell hash. The frequency dependence of the seafloor backscatter will be discussed in terms of its consistency, or lack thereof, with surficial roughness and shell-fragment scattering models.

Doppler Spectrum Analysis of Time-Evolving Sea Surface Covered by Oil Spills**Supported by the National Science Foundation for Distinguished Young Scholars of China under Grant No 61225002, and the Aeronautical Science Fund and Aviation Key Laboratory of Science and Technology on AISSS of China under Grant No 20132081015.

Based on the model of a contaminated sea surface that was proposed by Lombardini et al., the influence of the damping effect of oil films on the sea surface roughness spectrum and the geometrical structure of the sea surface is examined in detail by comparing with a clean sea surface. Furthermore, based on a quasi-stationary algorithm, a time series of backscattered echoes from a time-evolving sea surface covered by oil slicks is obtained by utilizing the frequency-domain numerical method of the parallel fast multiple method. Then, the Doppler spectrum is evaluated by performing a standard spectral estimation technique. Finally, the influence of the oil film damping effect on the Doppler spectrum of the backscattered echoes from time-evolving sea surface is investigated in detail by making a comparison of the Doppler spectrum of an oil-covered sea surface with the Doppler spectrum of a clean sea surface. The numerical simulations show that the damping effect of oil films has an influence on the Doppler spectrum signature for both horizontal-to-horizontal and vertical-to-vertical polarizations.

Application of point diffraction interferometry for middle spatial frequency roughness detection.

The possibilities of applying the point diffraction interferometry (PDI) method for the detection of the middle spatial frequency roughness of superpolished optical surfaces are analyzed. The point source used in the experiment is based on a single mode optical fiber with the subwavelength exit aperture size, which is about 0.25 μm. In a numerical aperture of 0.01 the reference wave root-mean-square deformation is less than 0.005 nm. It is theoretically shown that the possible diffraction-limited lateral resolution of PDI while measuring a spherical substrate of 100 mm curvature radius is about 8 μm. The experiment demonstrated the possibility of obtaining roughness spectra in the range 0.001-0.05 μm(-1). The surface map obtained by PDI, and the roughness spectra obtained by both the PDI and atomic-force microscopy methods are shown.