Method for high-accuracy reflectance measurements in the 2.5-microm region

Reflectance measurement with spectroradiometers in the solar wavelength region (0.4-2.5 microm) are frequently conducted in the laboratory or in the field to characterize surface materials of artificial and natural targets. The spectral surface reflectance is calculated as the ratio of the signals obtained over the target surface and a reference panel, yielding a relative reflectance value. If the reflectance of the reference panel is known, the absolute target reflectance can be computed. This standard measurement technique assumes that the signal at the radiometer is due completely to reflected target and reference radiation. However, for field measurements in the 2.4-2.5-microm region with the Sun as the illumination source, the emitted thermal radiation is not a negligible part of the signal even at ambient temperatures, because the atmospheric transmittance, and thus the solar illumination level, is small in the atmospheric absorption regions. A new method is proposed that calculates reflectance values in the 2.4-2.5-microm region while it accounts for the reference panel reflectance and the emitted radiation. This technique needs instruments with noise-equivalent radiances of 2 orders of magnitude below currently commercially available instruments and requires measurement of the surface temperatures of target and reference. If the reference panel reflectance and temperature effects are neglected, the standard method yields reflectance errors up to 0.08 and 0.15 units for 7- and 2-nm bandwidth instruments, respectively. For the new method the corresponding errors can be reduced to approximately 0.01 units for the surface temperature range of 20-35 degrees C.     

基于光源平移恢复物体法线和材质的算法

提出了一种基于光源平移恢复物体法线和材质的算法.光源平移时获得一组输入图像.根据输入图像将物体表面上的点分成纯漫反射点和混合点(包含漫反射和镜面反射的点).首先,根据镜面反射的原理求出混合点的法线.然后根据求出的法线用全局优化的迭代方法来恢复物体的材质.最后,根据不同输入图像中光源与物体的相对位置的不同,通过一个三角函数来恢复物体表面纯漫反射点的法线.分析对比实验结果和场景的真实参数表明,算法能够有效地恢复物体的法线和材质.     

Calculation method of reflectance distributions for computer-generated holograms using the finite-difference time-domain method

The research on reflectance distributions in computer-generated holograms (CGHs) is particularly sparse, and the textures of materials are not expressed. Thus, we propose a method for calculating reflectance distributions in CGHs that uses the finite-difference time-domain method. In this method, reflected light from an uneven surface made on a computer is analyzed by finite-difference time-domain simulation, and the reflected light distribution is applied to the CGH as an object light. We report the relations between the surface roughness of the objects and the reflectance distributions, and show that the reflectance distributions are given to CGHs by imaging simulation.     

Simulation on wavelength-dependent complex refractive index of liquids obtained by phase retrieval from reflectance dip due to surface plasmon resonance

A method for the calculation of the wavelength-dependent complex refractive index of absorbing liquid from reflectance in the vicinity of surface plasmon resonance (SPR) is presented. The calculation is based on the maximum entropy method (MEM). As an example, phase retrieval from a simulated SPR reflectance of a red colored liquid solution is carried out. It is proposed that MEM can be applied to wavelength-dependent complex refractive index assessment from reflectance of absorbing liquids in SPR measurement in wavelength scanning mode.     

Variational estimation of inhomogeneous specular reflectance and illumination from a single view

Estimating the illumination and the reflectance properties of an object surface from a few images is an important but challenging problem. The problem becomes even more challenging if we wish to deal with real-world objects that naturally have spatially inhomogeneous reflectance. In this paper, we derive a novel method for estimating the spatially varying specular reflectance properties of a surface of known geometry as well as the illumination distribution of a scene from a specular-only image, for instance, recovered from two images captured with a polarizer to separate reflection components. Unlike previous work, we do not assume the illumination to be a single point light source. We model specular reflection with a spherical statistical distribution and encode its spatial variation with a radial basis function (RBF) network of their parameter values, which allows us to formulate the simultaneous estimation of spatially varying specular reflectance and illumination as a constrained optimization based on the I-divergence measure. To solve it, we derive a variational algorithm based on the expectation maximization principle. At the same time, we estimate optimal encoding of the specular reflectance properties by learning the number, centers, and widths of the RBF hidden units. We demonstrate the effectiveness of the method on images of synthetic and real-world objects.     

Lidar in-space technology experiment measurements of sea surface directional reflectance and the link to surface wind speed

The dependence of sea surface directional reflectance on surface wind stress suggests a method for deriving surface wind speed from space-based lidar measurements of sea surface backscatter. In particular, lidar measurements in the nadir angle range from 10 degrees to 30 degrees appear to be most sensitive to surface wind-speed variability in the regime below 10 m/s. The Lidar In-space Technology Experiment (LITE) shuttle lidar mission of September 1994 provided a unique opportunity to measure directional backscatter at selected locations by use of the landmark track maneuver and to measure fixed-angle backscatter from the ocean surfaces on a global scale. During the landmark track maneuver the shuttle orbiter orientation and roll axis are adjusted continuously to maintain the lidar footprint at a fixed location for a duration of ~1 min. Several data sets were converted to calibrated reflectance units and compared with a surface reflectance model to deduce surface wind speeds. Comparisons were made with ERS-1 scatterometer data and surface measurements.     

Estimating visible through near-infrared spectral reflectance from a sensor radiance spectrum

We show that surface spectral reflectance can be separated from illumination effects in visible through near-infrared (350 nm-1740 nm) hyperspectral data by using only the information in a single radiance spectrum. The separation method exploits the fact that reflectance and illumination spectra typically lie in distinct subspaces. We present a comparison of a linear and a nonlinear algorithm for the separation. These algorithms compute an estimate of the spectral reflectance up to a scaling factor. In addition, we present an iterative method that is used to determine the starting point for the nonlinear algorithm. We also develop a method for selecting the dimension of the reflectance and illumination subspaces that is appropriate for material identification applications. The accuracy of the separation methods is quantified by application to noisy visible through near-infrared spectral data with a database of 107 materials and 3000 illumination spectra. The utility of the separation method for material identification is demonstrated with the same database. The results show that accurate reflectance recovery and material identification is possible by use of visible through near-infrared spectral data over the outdoor environmental conditions represented in this data set.     

纸张表面粗糙度和照射条件对纸张白度的影响

用基于测量仪器和样品散射特性的数学模型研究了纸张白度和纸张表面粗糙度的关系,比较了有和没有散射光中的镜面成分条件下的纸张白度和纸张表面粗糙度的关系,纸张白度是根据ISO/DIS 11475计算获得的.结果发现,所研究的纸张白度取决于纸张的表面粗糙度和所选择的照射条件,而纸张的色度坐标与两者无关.     

Multi-Carrier Generation in Organic-Passivated Black Silicon Solar Cells with Industrially Feasible Processes

The innate inverse Auger effect within bulk silicon can result in multiple carrier generation. Observation of this effect is reliant upon low high-energy photon reflectance and high-quality surface passivation. In the photovoltaics industry, metal-assisted chemical etching (MACE) to afford black silicon (b-Si) can provide a low high-energy photon reflectance. However, an industrially feasible and cheaper technology to conformally passivate the outer-shell defects of these nanowires is currently lacking. Here, a technology is introduced to infiltrate black silicon nanopores with a simple and vacuum-free organic passivation layer that affords millisecond-level minority carrier lifetimes and matches perfectly with existing solution-based processing of the MACE black silicon. Advancements such as the demonstration of an excellent passivation effect whilst also being low reflectance provide a new technological route for inverse Auger multiple carrier generation and an industrially feasible technical scheme for the development of the MACE b-Si solar cells.     

基于SYSTEM Ⅱ的新型微波中功率计量系统

SYSTEMⅡ功率传递系统是微波小功率计量领域内应用比较广泛的测试系统之一,通过对传统中功率计量方法的分析研究,提出了利用SYSTEMⅡ功率传递系统实现中功率计量的构建方案。采用低反射系数等效信号源结构,构成反射系数小、输出稳定、输出电平可调的中功率等效信号源;采用中功率衰减器和SYSTEMⅡ功率传递系统中含有的高精度终端式小功率座构成中功率传递标准,通过交替比较法,实现微波中功率计的高精度自动校准。     

利用非线性表面波评价材料疲劳损伤

采用非线性Rayleigh表面波检测方法,实现了不同疲劳阶段下钢试样拉伸和腐蚀疲劳损伤的测试与评价;基于楔块\换能器激发与接收声波方式,搭建非线性Rayleigh波检测系统,测量了不同激励水平下基波幅值平方与二次谐波幅值间的线性关系以及Rayleigh表面波二次谐波的累积效应;分别在拉伸载荷和腐蚀疲劳载荷下,采集非线性时域信号并进行频谱分析,测量声学非线性系数在不同疲劳阶段下变化趋势,并分析不同疲劳载荷对钢试样声学非线性系数的影响。实验结果表明:超声非线性系数与疲劳周期数呈单调递增关系,可以用声学非线性系数来表征材料的表面疲劳损伤程度;相比较周期性拉伸疲劳损伤,腐蚀疲劳试样的声学非线性系数会增大,是由于腐蚀环境会加重实验中钢试样的疲劳损伤程度。研究成果可为疲劳损伤无损检测与评价提供一定的指导意义。     

Atmospheric correction of ocean color sensors: analysis of the effects of residual instrument polarization sensitivity

We provide an analysis of the influence of instrument polarization sensitivity on the radiance measured by spaceborne ocean color sensors. Simulated examples demonstrate the influence of polarization sensitivity on the retrieval of the water-leaving reflectance rho(w). A simple method for partially correcting for polarization sensitivity-replacing the linear polarization properties of the top-of-atmosphere reflectance with those from a Rayleigh-scattering atmosphere-is provided and its efficacy is evaluated. It is shown that this scheme improves rho(w) retrievals as long as the polarization sensitivity of the instrument does not vary strongly from band to band. Of course, a complete polarization-sensitivity characterization of the ocean color sensor is required to implement the correction.     

核翼比法进行表面粗糙度的标定及测量

介绍了一种表面粗糙度标定及测量的新方法。通过标定一组标准样块的核翼比，可以实现该标定范围内待检样块的粗糙度测量，该方法稳定可靠，试验装置简单，数据处理方便，为表面粗糙度的非接触测量提供了较好的方案。     

基于涡流检测信号的金属曲面距离测量方法研究

为提高曲面试件的涡流测距精度,提出一种基于涡流信号差值的测距修正方法。该方法通过研究不锈钢平板试件与曲面试件涡流信号的不同,拟合计算出曲面涡流信号和平面涡流信号之间差值与曲面试件曲率的定量关系。利用这一函数关系,对不同曲率试件的测量结果进行补偿,可修正由于试件存在曲面造成的测量误差。通过实验进行可行性验证,对平板试件与不同直径轴件的测距结果进行误差分析。结果表明:相比于直接进行曲面涡流测距的传统手段,该方法将曲面试件测距误差降低60%以上,显著提高曲面测距精度,可应用于金属曲面涡流测距。     

Magnetorheological nanofinishing of BK7 glass for lens manufacturing

BK7 is a high-quality crown glass which is used where additional benefits such as temperature sensitive applications of fused silica glass are not required. Due to very low inclusion content with extremely low bubbles, BK7 glass can find its application in lens manufacturing. The present work focuses on nanofinishing of the BK7 glass specimen for ratifying its utility in practical application. A programmable logic controlled 3-axis motions are fed to the magnetorheological (MR) rotating tool for finishing the glass specimen. MR polishing fluid used for nanofinishing consists of deionized water, magnetic iron particles, and cerium oxide powder. Under the influence of magnetic field, the stiffened MR polishing fluid is assisted in reducing the surface roughness of glass up to nanolevel range. Optical properties such as transmittance, absorbance, and reflectance of finished BK7 glass are analyzed and found suitable for lens manufacturing. Results of higher surface quality with excellent finishing are obtained by the present MR finishing process. After 90?min of finishing, the surface roughness values R_a and R_q are reduced to 17 and 27?nm from the initial values of 41 and 57?nm, respectively. To study the surface morphology, scanning electron microscopy is performed on BK7 glass.     

Spectral calibration of hyperspectral imagery using atmospheric absorption features

One of the initial steps in the preprocessing of remote sensing data is the atmospheric correction of the at-sensor radiance images, i.e., radiances recorded at the sensor aperture. Apart from the accuracy in the estimation of the concentrations of the main atmospheric species, the retrieved surface reflectance is also influenced by the spectral calibration of the sensor, especially in those wavelengths mostly affected by gaseous absorptions. In particular, errors in the surface reflectance appear when a systematic shift in the nominal channel positions occurs. A method to assess the spectral calibration of hyperspectral imaging spectrometers from the acquired imagery is presented in this paper. The fundamental basis of the method is the calculation of the value of the spectral shift that minimizes the error in the estimates of surface reflectance. This is performed by an optimization procedure that minimizes the deviation between a surface reflectance spectrum and a smoothed one resulting from the application of a low-pass filter. A sensitivity analysis was performed using synthetic data generated with the MODTRAN4 radiative transfer code for several values of the spectral shift and the water vapor column content. The error detected in the retrieval is less than +/- 0.2 nm for spectral shifts smaller than 2 nm, and less than +/- 1.0 nm for extreme spectral shifts of 5 nm. A low sensitivity to uncertainties in the estimation of water vapor content was found, which reinforces the robustness of the algorithm. The method was successfully applied to data acquired by different hyperspectral sensors.     

Non-contact strain measurement using metal foil gauges with the application of the laser speckle method

This paper presents a new method to measure cyclic strain with no contact using metal foil gauges assisted by the laser speckle method. When aluminium foil is pasted on a specimen and the specimen is loaded cyclically, slip bands are produced on the foil surface. There is a fixed relation between density of the slip bands and the strain amplitude or loading cycles depending on the foil material. Thus the fatigue strain of the base metal can be estimated by observing the surface change of the metal foil by the slip bands at a constant number of loading cycles. The method presented in this paper is intended to make a non-contacting strain measurement by the application of the laser speckle technique for the detection of the surface change. This method is based on observation of the changes in a laser speckle pattern depending on the surface roughness and surface property changes of the foil caused by fatigue. The laser speckle pattern can be analysed automatically and quantitatively using an image processing system.     

Removal of surface reflection from above-water visible-near infrared spectroscopic measurements

Water quality estimation in fresh and marine water systems with in situ above-water spectroscopy requires measurement of the volume reflectance (rho(v)) of water bodies. However, the above-water radiometric measurements include surface reflection (L(r)) as a significant component along with volume reflection. The L(r) carries no information on water quality, and hence it is considered as a major source of error in in situ above-water spectroscopy. Currently, there are no methods to directly measure L(r). The common method to estimate L(r) assumes a constant water surface reflectance (rho(s)) of 2%, and then subtracts the L(r) thus calculated from the above-water radiance measurements to obtain the volume reflection (L(v)). The problem with this method is that the amount of rho(s) varies with environmental conditions. Therefore, a methodology was developed in this study for direct measurement of water volume reflectance above water at nadir view geometry. Other objectives of this study were to analyze the contribution of L(r) to the total water reflectance under various environmental conditions in a controlled setup and to develop an artificial neural network (ANN) model to estimate rho(s) from environmental conditions. The results showed that L(r) contributed 20-54% of total upwelling radiance from water at nadir. The rho(s) was highly variable with environmental conditions. Using sun altitude, wind speed, diffuse lighting, and wavelength as inputs, the ANN model was able to accurately simulate rho(s), with a low root mean square error of 0.003. A sensitivity analysis with the ANN model indicated that sun altitude and diffuse light had the highest influence on rho(s), contributing to over 82% of predictability of the ANN model. Therefore, the ANN modeling framework can be an accurate tool for estimating surface reflectance in applications that require volume reflectance of water.     

高强度钢30Cr3SiNiMoVA的疲劳特性研究

为了获得超高强度钢30Cr3SiNiMoVA的疲劳设计数据,对该材料进行了疲劳性能实验。分别对该材料的抛光和未抛光试样进行轴向拉压疲劳实验。用升降试验法测定材料的条件疲劳极限,用成组实验法在四级应力水平下测试其疲劳寿命。结合升降法所得的条件疲劳极限值和成组法实验数据,采用双参数最小二乘法拟合S-N曲线,运用概率方法求得P-S-N曲线。通过对两种试样的S-N曲线分析可知:未抛光试样的疲劳寿命要低于抛光试样的疲劳寿命,并且疲劳载荷级越低,两类试样之间的疲劳寿命差越大,抛光试样的疲劳极限大约是未抛光试样的1.4倍。相关实验现象表明30Cr3SiNiMoVA的疲劳寿命对试样表面粗糙状态非常敏感,建议该类材料在应用过程中要采取有效措施改善构件的表面状态。文中实验数据可为该材料的工程应用提供参考。     

Influence of surfactant addition for the texture etching process on multi-crystalline silicon wafer

This study investigates the effects of different recipes and concentrations of surfactant on the texture and reflectance of a multi-crystalline silicon wafer surface. The morphology of the surface was examined and photographed using a field emission scanning electronic microscope. The reflectance of the surface was measured and analyzed using a self-designed optical system. The results of this study show that a higher hydrocarbon-surfactant (CH-surfactant) concentration in the etchant resulted in a slower reaction time. The optimum concentration of CH-surfactant was 1%. However, there were many white bubbles in the etching process. The optimum recipe for surfactant included fluoride 2% to diminish these bubbles. The reflectance was less than 22% in visible light. This cost effective acid chemical etching method is suitable for texturing silicon surfaces on 50?nm nanostructures. This is a critical criterion for determining the optimum recipe for surface texturing of acidic etching in solar cells.