金银卡纸的镜面反射对颜色复制的影响

目的针对金银卡纸表面因具有强烈的镜面反射作用且印刷适性较差的缺点,研究金银卡纸镜面反射对印刷品颜色的质量控制。方法试验分析金银卡纸印刷镜面反射作用对印品明度值的影响,用曲线拟合的方法找出包含和不包含镜面反射作用测出的明度值之间的关系。结果经过检验分析,SCE条件下的测量数据相对于SCI明度偏小,这是因为SCE测量模式中,镜面反射光被排除在外面,只测量了漫射光。从青色的线性拟合图来看,所得线性拟合图大致为一条斜率为45°的直线。结论包含和不包含镜面反射明度值这2组数据之间存在数学关系,在实际应用中,可以考虑使用明度差这种线性关系来作为金银卡纸颜色控制和评价的依据。     

Polarization of specular reflection and near-specular scattering by a rough surface

Polarization of specular reflection and near-specular scattering (NSS) by a randomly rough surface is investigated by the use of a Mueller matrix formulation. The collective effect by a rough surface on the average specular field results in reflectance loss and polarization, which can be explained by an effective medium theory. Effects of random NSS can be represented by a scattering matrix that is partially coherent and polarized. The incoherent and unpolarized part of scattering causes depolarization, and the coherent and polarized parts of scattering change the apparent polarization properties of specular reflection. Results of a simulation and least-squares fit of ellipsometric data to the models including the NSS effect, for a black anodized aluminum sample, are presented. Simultaneous least-squares fits for both ellipsometric data and reflectance data at multiple angles of incidence at three different wavelengths gave approximately the same rms roughness, which agrees with the profilometric values reported previously.     

Multiparameter retrieval of water optical properties from above-water remote-sensing reflectance using the simulated annealing algorithm

Water-leaving radiance, measured just above the ocean surface, contains important information about near-surface or subsurface processes that occur on or below the deep ocean and coastal water. As such, retrieving seawater inherent optical properties (IOPs) is an important step to determining water type, subsurface light field, turbidity, pigment concentration, and sediment loading. However, the retrieval (or inversion) of seawater IOPs from just above water radiance measurements is a multiparameter nonlinear problem that is difficult to solve by conventional optimization methods. The applicability of the simulated annealing algorithm (SA) is explored as a nonlinear global optimizer to solve this multiparameter retrieval problem. The SA algorithm is combined with widely known semianalytical relations for seawater's IOPs to parameter invert these properties from simulated and measured water-leaving reflectance spectra. Furthermore, given the versatility of the SA algorithm, the scheme is extended to retrieve water depth from input reflectance data. Extensive tests and comparisons with in situ and simulated data sets compiled by the International Ocean-Color Coordinating Group are presented. Field data include reflectance spectra acquired with a handheld GER 1500 spectroradiometer and absorption measurements, performed with the AC-9 instrument on waters around Singapore's nearby islands.     

Rendering of specular surfaces in polygon-based computer-generated holograms

A technique is presented for realistic rendering in polygon-based computer-generated holograms (CGHs). In this technique, the spatial spectrum of the reflected light is modified to imitate specular reflection. The spectral envelopes of the reflected light are fitted to a spectral shape based on the Phong reflection model used in computer graphics. The technique features fast computation of the field of objects, composed of many specular polygons, and is applicable to creating high-definition CGHs with several billions of pixels. An actual high-definition CGH is created using the proposed technique and is demonstrated for verification of the optical reconstruction of specular surfaces.     

Mie scattering in the time domain. Part II. The role of diffraction

The p=0 term of the Mie-Debye scattering amplitude contains the effects of external reflection and diffraction. We computed the reflected intensity in the time domain as a function of the scattering angle and delay time for a short electromagnetic pulse incident on a spherical particle and compared it to the predicted behavior in the forward-focusing region, the specular reflection region, and the glory region. We examined the physical consequences of three different approaches to the exact diffraction amplitude, and determined the signature of diffraction in the time domain. The external reflection surface wave amplitude gradually replaces the diffraction amplitude in the angular transition region between forward-focusing and the region of specular reflection. The details of this replacement were studied in the time domain.     

A note on the solar elevation dependence of clear-sky snow albedo

Recent attempts to match the short-wave albedo of snow for clear skies using approximate spectral solar fluxes and solutions of the radiative transfer equation for snow were unsuccessful until a separate surface reflection term was introduced. A separate consideration of specular reflection from surface snow grains has been objected to as being ad hoc. Results based on a new parametrization of short-wave radiation are discussed. Compared with previous radiation models, the new model gives higher diffuse insolation and predicts higher albedos. The difference between observed and predicted albedos is substantially reduced without invoking surface reflection.     

Spectral and global diffuse properties of high-performance translucent polymer sheets for energy efficient lighting and skylights

A visible and near-IR spectral study is presented for a translucent smooth polymer sheet in which dopant particles are clear polymer with a refractive index close to that of the clear polymer host. Diffuse, specular, and total reflectance and transmittance and absorptance as a function of sheet thickness and dopant levels approach ideal behavior for lighting applications. A fourth optical parameter, side loss S(T), is introduced to fully account for the measured data. This covers radiation that is trapped by total internal reflection (TIR) and travels sideways sufficiently far, including to the sheet's edges, to miss detection on exit. S(T) has a strong spectral character, whereas total T and R spectra closely follow the spectrally flat wavelength dependence of the undoped clear sheet. Three distinct regimes are identified for the behavior with wavelength of the specular and diffuse components and are linked to rear surface TIR and side loss.     

风浪谱模型在高度计风速反演中的应用

依据粗糙海面电磁波镜面散射理论,将根据全波数范围内的风浪谱模型计算的标准化雷达后向散射截面与T/P卫星高度计测得的雷达后向散射截面(Ku波段)进行比较,实现了对高度计风速的反演.研究表明,在所选浮标附近海域,波龄因子对高度计风速反演存在较大影响.与目前高度计业务化算法相比,考虑波龄因子影响后,根据谱模型反演获得的风速与中国近海浮标风速之间均方根误差和平均偏差更小.由于波龄因子可以根据高度计测得有效波高以及业务化算法获得的风速得到,因此根据风浪谱模型反演获得的风速具有广泛的适用性.     

基于探测器的成象光谱仪绝对辐射定标方法

用一组窄带滤光片、简易辐亮度计和硅光二极管探测器设计了绝对型光谱辐亮度计。精确测量滤光片的光谱透过函数，计算辐亮度计的视场，标定探测器的绝对光谱响应度，成为绝对光谱辐亮度计，用来标定成象光谱和其它光学遥感器，并与基于光谱辐照度灯进行辐射定标的传统方法进行了比较。结果表明，基于探测器进行辐射定标的方法是一种提高光学遥感器定标精度的途径，而且是佐证其它定标方法可靠性的一种手段。     

Diffuse and specular reflectance from rough surfaces

We present a reflection model for isotropic rough surfaces that have both specular and diffuse components. The surface is assumed to have a normal distribution of heights. Parameters of the model are the surface roughness given by the rms slope, the albedo, and the balance between diffuse and specular reflection. The effect of roughness on diffuse reflection is taken into account, instead of our modeling this component as a constant Lambertian term. The model includes geometrical effects such as masking and shadowing. The model is compared with experimental data obtained from goniophotometric measurements on samples of tiles and bricks. The model fits well to samples with very different reflection properties. Measurements of the sample profiles performed with a laser profilometer to determine the rms slope show that the assumed surface model is realistic. The model could therefore be used in machine vision and computer graphics to approximate reflection characteristics of surfaces. It could also be used to predict the texture of surfaces as a function of illumination and viewing angles.     

Self-referencing substrates for optical interferometric biosensors

Optical interference is a powerful technique for monitoring surface topography or refractive index changes in a thin film layer. Reflectance spectroscopy provides label-free biosensing capability by monitoring small variations in interference signature resulting from optical path length changes from surface-adsorbed biomolecules. Spectral reflectance data can be acquired either by broad wavelength illumination and spectroscopy at a single point, thus necessitating scanning, or by varying the wavelength of illumination and imaging the reflected intensity allowing for acquisition of a spectral image of a large field of view simultaneously. In imaging modalities, intensity fluctuations of the illuminating light source couple into the detected signal, increasing the noise in measured surface profiles. This article introduces a simple technique for eliminating the effects of illumination light power fluctuations by fabricating on-substrate self-reference regions to measure and normalize for the incident intensity, simplifying the overall platform for reflection or transmission-based imaging biosensors. Experimental results demonstrate that the sensitivity performance using self-referencing is equivalent or better than an optimized system with an external reference.     

Size Effect in the High-Field Magnetoconductivity of Pure Metal Single Crystals

The magnetoresistivity of tungsten single crystals with a residual resistivity ratio of up to 70,000 was measured in the temperature range from 4.2 to 55 K in a magnetic field of 10 T. The size effect, i.e., the linear dependence of the magnetoconductivity on the inverse sample dimensions, has been observed in the high-field magnetoconductivity. The experiments show that this phenomenon can be used to separate and study the surface and volume contributions to the magnetoresistivity of pure single crystals of compensated metals from liquid helium temperature up to approximately 25 K. It is shown that the specular reflection coefficient of the conduction electrons for pure metals in high magnetic fields can be determined in this way.     

小斜率近似方法分析粗糙界面声散射问题

利用小斜率近似方法计算了起伏海面的声散射特性,得到了具有高斯分布粗糙海面的平均反射系数（即镜反射系数）计算公式,并与微扰法和Kirchhoff近似做了比较,结果表明小斜率近似是一种非常有效的分析起伏表面散射特性的近似方法。最后讨论了海面镜反射系数随海面的不平整度（波浪的均方根高度）、声波频率和声波入射方向的变化关系,得出了只有在声波波长和起伏波浪高度可比拟时,才有明显的镜反射的结论。这为分析浅海目标声散射特性时,选择是否需要考虑海面（海底）所引起的多途效应提供了理论依据。     

Effects of a butterfly scale microstructure on the iridescent color observed at different angles

Multilayer thin-film structures in butterfly wing scales produce a colorful iridescence from reflected sunlight. Because of optical phenomena, changes in the angle of incidence of light and the viewing angle of an observer result in shifts in the color of butterfly wings. Colors ranging from green to purple, which are due to nonplanar specular reflection, can be observed on Papilio blumei iridescent scales. This refers to a phenomenon in which the curved surface patterns in the thin-film structure cause the specular component of the reflected light to be directed at various angles while affecting the spectral reflectivity at the same time by changing the optical path length through the structure. We determined the spectral reflectivities of P. blumei iridescent scales numerically by using models of a butterfly scale microstructure and experimentally by using a microscale-reflectance spectrometer. The numerical models accurately predict the shifts in spectral reflectivity observed experimentally.     

Width of the specular peak perpendicular to the principal plane for rough surfaces

The bidirectional reflectance distribution function (BRDF) model developed by Torrance and Sparrow [J. Opt. Soc. Am. 57, 1105-1114 (1967)] is used to describe the specular reflection of rough surfaces. We compare this model with the BRDF measurements of four manmade surfaces with different roughnesses. The model can be used to describe the basic features of the measured BRDFs. We found that the width of the specular peak perpendicular to the principal plane decreases strongly with an increasing illumination zenith angle in the data as well as in the model. A model analysis shows that the width is approximately proportional to the cosine of the illumination angle theta(i), and the deviations are determined by the roughness of the surface. This relationship is accompanied by an increase in reflectance in the specular direction in the principal plane that is 1/cos theta(i) stronger than the increase for a perfectly smooth surface.     

Basis for spectral curvature algorithms in remote sensing of chlorophyll

A simple, empirically derived algorithm for estimating oceanic chlorophyll concentrations from spectral radiances measured by a low-flying spectroradiometer has proved highly successful in field experiments in 1980-82. The sensor used was the Multichannel Ocean Color Sensor, and the originator of the algorithm was G. W. Grew, NASA CP-2188 (1981). This paper presents an explanation for the algorithm based on the optical properties of waters containing chlorophyll and other phytoplankton pigments and the radiative transfer equations governing the remotely sensed signal. The effects of varying solar zenith, atmospheric transmittance, and interfering substances in the water on the chlorophyll algorithm are characterized, and applicability of the algorithm is discussed.     

Enhanced specular peaks in diffuse light scattering from weakly rough metal surfaces

We employ Monte Carlo techniques based on the reduced Rayleigh equations to study an enhanced specular peak that appears in the light scattered from weakly rough metal surfaces. This peak is not associated with the specular reflection but instead appears, with finite angular width, at the specular angle of the mean diffusely scattered intensity. As is the case with backscattering enhancement, the specular peak arises from the interference of contributions of multiple-scattering processes related to surface plasmon polariton excitation. We demonstrate that the specular peak is seen clearly for surface roughness that has a conventional Gaussian power spectrum. Further, we show that the peak appears more distinctly for roughness whose power spectrum has a new rectangular form, which is proposed here with the intent of better isolation of the scattering processes essential to the specular peak. Finally, for a pair of rough surfaces that have appropriately correlated surface roughness, it is found that the cross correlation of scattered amplitudes presents a well-isolated specular peak, which directly demonstrates the constructive interference that produces the effect.     

Split off-specular reflection and surface scattering from woven materials

We measured radiance distributions for black lining cloth and copper gauze using the convenient technique of wrapping the materials around a circular cylinder, irradiating it with a parallel light source and collecting the scattered radiance by a digital camera. One family of parallel threads (weave or weft) was parallel to the cylinder generator. The most salient features for such glossy plane weaves are a splitting up of the reflection peak due to the wavy variations in local slopes of the threads around the cylinders and a surface scattering lobe due to the threads that run along the cylinder. These scattering characteristics are quite different from the (off-)specular peaks and lobes that were found before for random rough specular surfaces. The split off-specular reflection is due to the regular structures in our samples of man-made materials. We derived simple approximations for these reflectance characteristics using geometrical optics.     

Luminance-based specular gloss characterization

Gloss is a feature of visual appearance that arises from the directionally selective reflection of light incident on a surface. Especially when a distinct reflected image is perceptible, the luminance distribution of the illumination scene above the sample can strongly influence the gloss perception. For this reason, industrial glossmeters do not provide a satisfactory gloss estimation of high-gloss surfaces. In this study, the influence of the conditions of illumination on specular gloss perception was examined through a magnitude estimation experiment in which 10 observers took part. A light booth with two light sources was utilized: the mirror image of only one source being visible in reflection by the observer. The luminance of both the reflected image and the adjacent sample surface could be independently varied by separate adjustment of the intensity of the two light sources. A psychophysical scaling function was derived, relating the visual gloss estimations to the measured luminance of both the reflected image and the off-specular sample background. The generalization error of the model was estimated through a validation experiment performed by 10 other observers. In result, a metric including both surface and illumination properties is provided. Based on this metric, improved gloss evaluation methods and instruments could be developed.     

Infrared reflection-absorption spectra of metal-effect coatings

The results of studies of infrared reflection-absorption spectra of metal-effect coatings are presented in this paper. Such coatings consist of metallic flakes that are dispersed in a polymer binder. The spectra show two distinct phenomena. One is due to the polymer matrix. The other is due to metallic flakes that are dispersed inside the layer. The polymer binder causes narrow spectral lines that give a thickness-dependent intensity and position. Metallic flakes change the average baseline of this spectrum over the entire infrared spectral region. This particular effect was evaluated using a simple rough-surface model. Two parameters of the model, the root-mean-square roughness and the correlation length of the rough surface, described the reflection of the partial beams on the metal flake surfaces and scattering on flakes boundaries. The other two parameters are the specular reflectance and the diffuse reflectance of the plane untextured interface between the polymer matrix and the metal flake surface. Various metal-effect coatings within the same polymer binder were analyzed. The effect of each metal flake dispersion was evaluated by the parameters within the rough-surface model. The results were analyzed in terms of the size and the loadings of flakes that were used in the coatings.