Model of bidirectional reflectance distribution function for metallic materials

Based on the three-component assumption that the reflection is divided into specular reflection,directional diffuse reflection,and ideal diffuse reflection,a bidirectional reflectance distribution function（BRDF） model of metallic materials is presented.Compared with the two-component assumption that the reflection is composed of specular reflection and diffuse reflection,the three-component assumption divides the diffuse reflection into directional diffuse and ideal diffuse reflection.This model effectively resolves the problem that constant diffuse reflection leads to considerable error for metallic materials.Simulation and measurement results validate that this three-component BRDF model can improve the modeling accuracy significantly and describe the reflection properties in the hemisphere space precisely for the metallic materials.

Bidirectional reflectance one-dimensional rough distribution function modeling of surface in the microwave band

In this study, the bidirectional reflectance distribution function （BRDF） of a one-dimensional conducting rough surface and a dielectric rough surface are calculated with different frequencies and roughness values in the microwave band by using the method of moments, and the relationship between the bistatic scattering coefficient and the BRDF of a rough surface is expressed. From the theory of the parameters of the rough surface BRDF, the parameters of the BRDF are obtained using a genetic algorithm. The BRDF of a rough surface is calculated using the obtained parameter values. Further, the fitting values and theoretical calculations of the BRDF are compared, and the optimization results are in agreement with the theoretical calculation results. Finally, a reference for BRDF modeling of a Gaussian rough surface in the microwave band is provided by the proposed method.

Three-Component Model for Bidirectional Reflection Distribution Function of Thermal Coating Surfaces

We present a bidirectional reflection distribution function （BRDF） model for thermal coating surfaces based on a three-component reflection assumption, in which the specular reflection is given according to the microfacet theory and Snell＇s law, the multiple reflection is considered Nth cosine distributed, and the volume scattering is uniformly distributed in reflection angles according to the experimental results. This model describes the reflection characteristics of thermal coating surfaces more completely and reasonably. Simulation and measurement results of two thermal coating samples SR107 and S781 are given to validate that this three-component model significantly improves the modeling accuracy for thermal coating surfaces compared with the existing BRDF models.

Simulation Calculation and Distribution Characteristics of Terrain Reflected Radiation in Fujian Province

[Objective] The aim was to study the distribution characteristics of terrain reflected radiation in Fujian Province.[Method] Based on solar radiation data,digital elevation model (DEM) and surface meteorological observation data in Fujian Province,plus surface albedo obtained by using remote sensing inversion method,the distribution of terrain reflected radiation in Fujian Province from 1988 to 2007 was simulated,and then its temporal and spatial distribution characteristics was studied.[Result] The simulation results of terrain reflected radiation in Fujian Province was credible.Terrain reflected radiation in Fujian Province was the highest in July (about 160 MJ/m2) and lowest in January (about 60 MJ/m2),and it was obviously higher from May to August compared with other months,while the order of terrain reflected radiation in four seasons was summer>spring>autumn>winter,and complex terrain affected the distribution of terrain reflected radiation greatly,especially in autumn and winter when sun elevation angle was small.In addition,terrain reflected radiation in most areas of Fujian Province was below 100 MJ/m2,and it was high in Ningde,Sanming and Nanping City in northern Fujian,while the maximum value (630 MJ/m2) could be found in Dong’an Island in Xiapu County in Ningde City and had good utilization value.[Conclusion] The study could provide theoretical foundation for the development and utilization of solar energy resources under complex terrain in China.

Modeling bidirectional reflection distribution function of microscale random rough surfaces

The radiative properties of three different materials surfaces with one-dimensional microscale random roughness were obtained with the finite difference time domain method(FDTD) and near-to-far-field transformation.The surface height conforms to the Gaussian probability density function distribution.Various computational modeling issues that affect the accuracy of the predicted properties were discussed.The results show that,for perfect electric conductor(PEC) surfaces,as the surface roughness increases,the magnitude of the spike reduces and eventually the spike disappears,and also as the ratio of root mean square roughness to the surface correlation distance increases,the retroreflection becomes evident.The predicted values of FDTD solutions are in good agreement with the ray tracing and integral equation solutions.The overall trend of bidirectional reflection distribution function(BRDF) of PEC surfaces and silicon surfaces is the same,but the silicon's is much less than the former's.The BRDF difference from two polarization modes for the gold surfaces is little for smaller wavelength,but it is much larger for the longer wavelength and the FDTD simulation results agree well with the measured data.In terms of PEC surfaces,as the incident angle increases,the reflectivity becomes more specular.

Temporal response of laminated graded-bandgap GaAs-based photocathode with distributed Bragg reflection structure:Model and simulation

To describe the dynamic response characteristics of the laminated graded-bandgap GaAs-based photocathode with distributed Bragg reflection structure,a general theoretical temporal response model is deduced by combining the unsteady continuity equation and numerical calculation method.Through the model,the contribution of the distribution Bragg reflec-tion structure and graded-bandgap emission layer to the temporal response are investigated.Meanwhile,the relationships between the temporal response characteristics of the laminated GaAs-based photocathode and different structural parame-ters are also analyzed,including average electron decay time,emission layer thickness,and incident light wavelength.It is found that the introduction of distribution Bragg reflection(DBR)layer solves the discrepancy between the absorption capability of the emission layer and the temporal response.Moreover,the distributed Bragg reflection layer can improve the time response by optimizing the initial photoelectron distribution.The improvement effect of the DBR layer on the temporal response is enhanced with the emission layer thickness decreasing or the incident light wavelength increasing.These results explain the effect of the DBR layer of the photocathode on the dynamic characteristics,which can offer a new insight into the dynamic research of GaAs-based photocathode.

Understanding the Variability of Z-R Relationships Caused by Natural Variations in Raindrop Size Distributions(DSD):Implication of Drop Size and Number

In the issue of rainfall estimation by radar through the necessary relationship between radar reflectivity Z and rain rate R (Z-R), the main limitation is attributed to the variability of this relationship. Indeed, several pre-vious studies have shown the great variability of this relationship in space and time, from a rainfall event to another and even within a single rainfall event. Recent studies have shown that the variability of raindrop size distributions and thereby Z-R relationships is therefore, more the result of complex dynamic, thermody-namic and microphysical processes within rainfall systems than a convective/stratiform classification of the ground rainfall signature. The raindrop number and size at ground being the resultant of various processes mentioned above, a suitable approach would be to analyze their variability in relation to that of Z-R relation-ship. In this study, we investigated the total raindrop concentration number NT and the median volume di-ameter D0 used in numerous studies, and have shown that the combination of these two ‘observed’ parame-ters appears to be an interesting approach to better understand the variability of the Z-R relationships in the rainfall events, without assuming a certain analytical raindrop size distribution model (exponential, gamma, or log-normal). The present study is based on the analysis of disdrometer data collected at different seasons and places in Africa, and aims to show the degree of the raindrop size and number implication in regard to the Z-R relationships variability.

Smart Solar Charging： Bi-Directional AC Charging （V2G） in the Netherlands

It is to be expected that the number of electric vehicles will be growing in the near future. This trend comes together with the development of smaller decentralized generation units, like PV （photo voltaic）. Together with the change on demand side that comes with the global ＂electrification＂, this can lead to serious grid congestion in low voltage grids and massive grid investments in solving this congestion. Smart charging can partly solve this issue, but with using a connected EV （electric vehicle） as a small distribution unit, combined with bi-directional charging or V2G （vehicle-to-grid） technology, these investments can be reduced to a minimum. In Lombok, Utrecht, the Netherlands, an innovative pilot was initiated with smart solar charging stations, shared electric vehicles and AC （alternating current） V2G technology. This unique combination proves that EVs are an opportunity for the grid rather than a threat. A unique partnership with OEM Renault was established to develop an AC V2G vehicle product line and work on open standardized communication between the EV, the charging station and the grid.

基于反射系数谱的配电电缆局部缺陷识别定位

传统配电电缆在局部缺陷识别与精准定位上灵敏度较差,位置范围识别受到限制,为解决现有技术在配电电缆缺陷诊断上存在的不足,提出一种基于反射系数谱的配电电缆局部缺陷识别定位方法。首先依据电缆分布参数模型,获得配电电缆完好状态与存在局部缺陷段的反射系数谱,然后利用广义正交积分法,将反射系数谱的虚部从频域转换到空间域,建立积分诊断图,得到具有直观性的定位图谱,根据积分诊断图实现配电电缆局部缺陷的识别与精准定位,方法适用于同时存在多处电缆缺陷的情况。最后,在实验室50 m长的配电电缆上制作老化与破损两种缺陷,用于验证所提方法的有效性。仿真和实验结果表明,该方法对不同缺陷情况均具有较高的识别精度,定位误差小于0.15 m。

激光散射特性的红外瞄准镜基线检测方法

为提升武器射击精度,设计激光散射特性的红外瞄准镜基线检测方法。通过固定瞄准镜并利用黑体发射红外激光,在镜子反射后形成红外平行光束,并在瞄准镜视场内生成靶标的像。通过调整瞄准镜分划中心与靶标像中心重合,实现基线检测。采用双向反射分布函数和基尔霍夫近似理论的驻留相位近似法,分析红外激光的散射特性及波长与散射角对成像精度的影响,从而提高基线检测的精度。实验证明:当入射波长在9.5μm左右时,射击目标粗糙度为8μm时,双站极化散射系数最低,在1.0左右;当散射角在29°左右时,射击目标粗糙度为8μm时,双站极化散射系数最低在0.146左右;校正后目标位置偏差平均为0.01 m。

点云空间与反射强度融合的非结构化道路可行驶区域检测

可行驶区域检测旨在检测和提取智能车辆在道路上可行进的区域,目前主流的检测方法主要基于三维激光雷达的空间特征实现,难以处理路面边缘无清晰空间特征的非结构化道路.为此,本文提出了一种基于点云空间和反射强度融合的非结构化道路可行驶区域检测方法.首先,通过融合反射强度因子改进了基于空间特征的柱坐标系检测模型;然后,使用强度和降维空间检测对检测精度较低的环形检测模型进行优化,并将其与柱坐标系检测模型联合使用以提高方法检测准确率;最后,在自录实际道路数据集上进行对比实验.实验结果表明本文方法显著提高了非结构化道路可行驶区域检测的成功率与精确率,在结构化道路上也具有良好效果.

改进鲸鱼优化算法的壁面红外反射特性求解

壁面的红外反射特性由双向反射分布函数(BRDF)表征和求解。目前BRDF测量需要大量实验数据,同时存在精度不高的问题。通过构建壁面反射特性测试平台,使用MR170型傅立叶红外光谱辐射计获取2~15μm波段下入射角度和各个反射角度的目标辐射亮度。针对隐身目标,应用RBF网络对3~5μm以及8~14μm波段的辐射亮度曲线进行拟合,排除大气干扰,进而求解出上述两个波段隐身目标的BRDF值。为了解决BRDF模型精度不高的问题,提出了改进的鲸鱼优化算法(IWOA),对BRDF模型参数进行反演,并设计了基于BRDF的反射率求解方法。IWOA对BRDF计算模型参数反演有良好的效果。根据反射法,应用所得到的BRDF数据求解得到的反射率为0.5496,相对误差为6.17%,满足工程需求。

强光背景下主动偏振成像方法

针对传统光电探测方法在强光背景下目标探测对比度低的问题,本文提出一种基于激光照明的主动偏振成像方法。首先构建激光入射双向反射分布模型、激光入射偏振双向反射分布模型以及激光照明的目标表面偏振度模型,并分析3种典型目标材料偏振特性与束散角之间的耦合关系。然后在暗室可控条件下开展逆光观测实验,验证目标偏振特性受激光束散角的影响。实验结果表明:强光背景下主动偏振成像目标对比度与传统被动强度成像相比提升了86.11%,不同束散角下不同目标材料的可见光偏振特性间存在差异,金属材质相对于非金属材质的线偏振度提升更高,实验结果与理论分析具有较好的一致性。最后,在室外开展太阳逆光观测实验,验证了研究方法在室外高强光、远距离下依旧具有适用性。本研究为提升强光背景下的目标精准感知能力奠定了理论基础。

高反射釉料对不同厚度光伏玻璃断裂强度的影响

高反射釉料常被涂覆在光伏玻璃上以提升其光电转化效率,然而,高反射釉料对光伏玻璃断裂强度的影响尚不明确。本文采用双环测试和四点弯曲测试定量研究了玻璃厚度(1.55、1.86和2.89 mm)、釉料种类(A和B)、加载速率(2、20、50 mm/min)及上压头受力面(釉料面、玻璃面)等对光伏玻璃断裂强度的影响,并结合Weibull分布分析变量对光伏玻璃断裂强度的影响。研究结果表明,两种高反射釉料都能显著降低光伏玻璃的断裂强度,其中,在釉料面朝下时,双环测试的断裂强度降低超过72%,远超过四点弯曲强度的降低幅度(26%~46%)。此外,随着玻璃厚度的下降,断裂强度显著降低,例如,四点弯曲测试中,2.89 mm厚度带釉料的全钢化光伏玻璃断裂强度为104 MPa,而1.55和1.86 mm厚度半钢化光伏玻璃的断裂强度仅为68和73 MPa。通过扫描电子显微镜发现,釉料层与光伏玻璃基体中的微孔等缺陷是导致光伏玻璃断裂强度下降的主要原因。

典型多尺度海面结构体辐射散射方向-光谱特性计算与分析

针对3级以上海况的高精度海洋场景红外仿真问题,提出一种“先拆后建”的研究思路:将含泡沫和破碎波的多尺度海面抽象为粗糙海面、泡沫、破碎波的组合,进而拆解出“粗糙海面”、“含泡沫粗糙海面”、“含破碎波粗糙海面”3类典型多尺度海面结构体,最后通过海面栅格化、结构体匹配、方向-光谱特性重构渲染等方法,由3类典型多尺度结构体方向-光谱特性组合重构大范围海面辐射散射特性,完成多尺度海面“气-面-体”耦合辐射/散射特性的计算。对拆解出的3类典型多尺度海面结构体分别开展多尺度耦合辐射、散射特性建模研究,构建3类多尺度海面结构体辐射散射方向-光谱特性计算模型,并对结构体辐射散射方向-光谱特性的影响因素进行分析,结果表明:随着海面风速的增大,海面典型结构体中的泡沫厚度及气泡浓度逐渐增大,使得结构体的散射能力增强,从而增大结构体的双向反射分布函数;随着探测波长的增大,海水的吸收性显著增强,导致不同风速条件下结构体双向反射分布函数之间的差异显著增大;对于不同的入射角,结构体双向反射分布函数最大值对应的天顶角随入射天顶角的变化逐渐发生变化。

基于BRDF可见光偏振成像技术的海面溢油油种识别研究

海上溢油事件发生后需要及时判断溢油种类,为溢油事故处置提供及时有效的应对措施。本文利用BRDF多角度测量装置和可见光偏振相机对不同油种和清洁海水进行观测,基于可见光偏振特征筛选出最佳观测Stokes参量和对应观测几何,构建了清洁海水和不同油种数据集,并建立了基于BRDF偏振特征的DBN溢油油种识别模型。研究发现,在实验室可控条件下,相对方位角–60°、0°、–30°组合时油种识别效果较好,光源天顶角和相机观测角二者在接近±50°时识别效果较好;多次重复实验显示,海水、原油、重油、汽油、柴油、棕榈油的最优识别率分别为90%、86.27%、84%、80.44%、82.08%和82%;基于可见光偏振特征所建立的油种识别模型,对于海面溢油种类区分具有较好的效果。

空间特性光谱反演及对户外光谱修正的可行性研究

户外高光谱探测可以快速获取样品的光谱信息,但受环境光线和样品二向反射特性的影响,采集到的光谱并不能准确反映样品的真实信息,对户外探测精度有一定影响。为了提高户外高光谱探测精度,提出了一种使用空间特性光谱对户外光谱进行修正的方法,以冬枣、红提、小白杏为研究对象,使用Walthall、Shibayama、Ross-li、Roujean与Rahman这5种BRDF模型反演3种果品的空间特性光谱,利用反演的空间特性光谱对户外光谱进行修正,之后分别建立暗室光谱、户外光谱与修正光谱的品质预测模型。反演结果表明:3种果品的空间特性光谱均有较好的反演效果,反演误差从低到高依次为冬枣、小白杏、红提,平均决定系数R2分别为0.957、0.947、0.927,平均误差分别为3.56%、4.90%、8.23%;5种BRDF模型中,Walthall模型的反演效果最佳,平均决定系数R2与误差分别为0.949、5.33%,Ross-li模型的反演效果最差,平均决定系数与误差分别为0.934、6.05%。户外光谱修正结果表明:户外光谱经过修正后噪声减少,光谱更为平滑,且光谱趋势与暗室光谱一致,受反演效果影响,冬枣光谱的修正效果最佳,而红提与小白杏的修正光谱中噪声较多。品质预测模型结果表明:3种果品的品质预测模型预测效果差异较大,从高到低依次为冬枣、小白杏、红提,可能与3种果品的品质不同有关;5种BRDF模型得到的修正光谱所建立的模型预测效果不同,但无显著差异;预测模型中,使用暗室光谱建立的预测模型最优,修正光谱建立的模型预测能力优于户外光谱建立的模型,表明户外光谱经过修正后模型预测能力得到提升。BRDF模型能够较好地反演果品的空间特性光谱,修正后的光谱与暗室光谱较为接近,修正光谱建立的模型优于户外光谱建立的模型,表明使用空间特性光谱对户外光谱进行修正的方法是可行的,可为提高户外无损检测的精度提供一种新的思路。

自由边界影响下定向断裂爆破裂纹尖端应力分布与扩展机理

天然岩体常含自由边界,对定向断裂爆破产生干扰。为探究自由边界对定向断裂爆破的影响,采用爆炸焦散线方法和高速摄影技术,研究了含自由边界时定向爆炸裂纹尖端的应力分布和扩展机理。自由边界的反射P/S波作用于定向爆炸裂纹,改变了裂尖应力分布,产生了“弧线形”裂纹扩展路径。定向爆炸裂纹扩展可分为3个阶段。(1)反射波作用前:裂尖受爆生气体“气楔”作用,产生Ⅰ型断裂,并沿直线扩展。(2)反射波作用时:反射P/S波均使裂尖受张拉-剪切作用,产生Ⅰ-Ⅱ复合型断裂,裂纹偏转趋向自由边界;在反射P波的作用下裂尖产生畸变焦散斑,裂尖应力由K场主导变为非K场主导,而在反射S波的作用下裂尖应力恢复为K场主导。(3)反射波作用后:裂尖在惯性作用下恢复为Ⅰ型断裂,沿直线扩展。在明确反射P/S波对定向爆炸裂纹作用的基础上,推导了自由边界影响下定向断裂爆破炮孔间距的计算公式,可为精细化定向断裂爆破提供理论参考。

复杂场景散射特性的参数化仿真模型

针对复杂场景电磁散射特性的实时仿真需求,提出了一种基于散射中心的散射特性参数化仿真模型。首先基于数字高程数据,利用蒙特卡罗法补充粗糙度信息,构建复杂地形网格模型;再利用双向反射分布函数修正的属性散射中心(bidirectional reflection distribution function modified attribute scattering center,BRDF-ASC)模型建立参数化仿真模型。数值实验结果表明:所提算法仿真的典型山峰和沙丘地形的雷达散射截面积(radar cross section,RCS)与物理光学(physical optics,PO)法仿真的RCS的均值误差低于3.6 dBsm;与大型海港的实测合成孔径雷达(synthetic aperture radar,SAR)图像进行对比,其参数化散射模型仿真SAR图像的变更检出率为0.1097,验证了所提算法的可行性。

共同富裕背景下社会力量参与第三次分配:时代内涵、实践形态与路径省思

第三次分配是社会力量自愿通过慈善活动与志愿服务对各类资源进行重新配置的社会活动,是对初次分配和再分配的补充性制度安排,对于推进共同富裕具有重要价值。社会力量参与第三次分配的主要形式为慈善组织进行信息收集与募集善款、市场企业进行利益与资源共享、社会个人进行捐赠与志愿服务,但同时也面临着结构失衡、成长受阻与信任危机等现实困境。结合我国实际情况,应从法律层面、制度层面、治理层面、环境层面与监督层面反思社会力量参与第三次分配的路径:通过完善《慈善法》相关法律体系优化社会力量的参与渠道,通过公正合理的制度措施激发社会力量的参与热情,通过构建“善”治导向的共同体促进社会力量的参与长久,通过营造积极健康的慈善生态稳定社会力量的参与环境,通过建立多元协同的监督机制改善社会力量的参与实践,旨在充分发挥社会力量在第三次分配中的重要作用,在高质量发展中扎实推进共同富裕。