完全氧化DZ125的双向反射特性实验研究

作为燃气轮机的核心部件，涡轮叶片长期在上千度的高温下工作，为了保证叶片安全可靠地运行，需要对其温度进行实时的监测。辐射测温是目前涡轮叶片非接触式测温的主流方法，其测温精度与叶片材料反射特性关系密切，如何预测不同方向反射能量的大小，减小反射辐射对测温结果的影响是目前研究的难点。为了预测叶片反射能量大小，提高辐射测温的准确性，对涡轮叶片常见材料——完全氧化DZ125的双向反射分布函数(BRDF)进行研究。采用对比法作为实验测量的方法，先分析了BRDF对比法测量原理及数据处理方法，之后自主搭建了试验台，在温度分别为25, 900和1 100℃,波长分别为1 060, 1 550和1 908 nm的条件下，控制入射天顶角及反射天顶角在0°～60°范围变化，方位角在0°～180°范围变化，测量计算出了多组BRDF值，分析了各种因素对完全氧化DZ125的BRDF的影响。最后采用Modified Phong模型对BRDF测量值进行了拟合，并与实验测量结果进行了对比，得到了较好的结果。研究结果表明，温度、波长对完全氧化DZ125的BRDF影响较小，在涡轮叶片工作的温度范围变化不大，辐射波长变化不大时，...     

电子入射角度对聚酰亚胺二次电子发射系数的影响

采用具有负偏压收集极的二次电子发射系数测试系统, 对聚酰亚胺样品的二次电子发射系数与入射电子角度和入射电子能量的关系进行了测量. 测量结果表明, 在电子小角度入射样品的情况下, 随着入射角度的增加, 二次电子发射系数单调增加, 并符合传统的规律, 但是在电子大角度入射时, 却与此不符合. 测量显示, 出现偏差时对应的临界电子入射角度随着入射电子能量的降低而减小. 采用简化的电子弹性散射过程和卢瑟福弹性散射截面公式对这种偏差的出现进行了分析, 并推导出修正后的二次电子发射系数的计算公式. 修正后的二次电子发射系数的计算结果更加符合实验结果.     

掩埋目标声散射特性及其实验

基于变分原理建立2D-FE弱形式解模型,针对轴对称掩埋目标进行散射远场的快速、高精度数值计算。入射波垂直于对称轴,给出:掩埋深度不变,以1°为间隔,改变掠射角所得到目标散射声压级相对于垂直海底照射获得结果的差值随频率、掠射角变化的表达式;掠射角不变,以0.1m为间隔,改变掩埋深度得到的散射声压级相对于浅掩埋条件下获得结果的差值随频率、深度变化的表达式。实验结果表明:在回波最强的正横方向,掩埋弹性目标表现出的共振散射特性与在自由场空间中具有相似性,表明了掩埋条件下目标内填充的透射和表面环绕波理论的适用性,验证了大掠射角入射得到散射声压级差值的变化规律。研究成果对宽带、高频入射声波探测更深掩埋目标提供思路。      

��ԭ���ڵ�һ�ڲ��������ɢ����Ϊ�ķ��Ӷ���ѧģ��

The scattering behaviour of H atoms on Be surface by molecular dynamics simulations was reported in this paper. When the incident energy increases from 1 to 9eV, the outcome shows the H atoms scattering rate decrease with incident energy increasing, and increase with incident angle increasing. When incident energy is 1eV, all of incident H atoms scatter above the Be surface. When incident energy are 5 and 9eV, 14.7% and 35.8% of H atoms inject into the Be sample and then scatter, respectively, and incident depths increase with energy increasing. Scattering density and energy as function of scattering angle were also discussed.     

五角棱镜角度误差对建立大尺寸平面基准的影响

用一准直光束作为基线，通过９０°折转的五角棱镜扫描，建立一个参考基准面在大尺寸测量中是一种行之有效的方法。在理想条件下，五角棱镜的折转角不受入射角的影响。由于有加工误差，光束的折转角将偏离９０°，且入射光线与扫描轴间的角运动也会影响该偏转角。本文分析了五角棱镜角度误差和扫描精度对光束折转角的影响。结果表明，五角棱镜的制造误差和工作状态将引起测量带误差，该误差是一个固定的系统误差，可以通过预先对所用的五角棱镜进行标定，在数据处理中予以修正。实验结果表明，修正后的结果具有很高的精度     

大气中目标背景对比度及其影响因素的数值分析

 从辐射传输理论出发，利用离散纵标法软件包（DISORT），计算了典型大气条件下0.55μm波长的目标背景对比度，分析了观察者的天顶角和方位角、水平能见度、垂直高度、太阳的天顶角和方位角以及气溶胶单次散射反照率对目标背景对比度的影响。结果表明：目标背景对比度随着观察者天顶角余弦的增加而增加；随着太阳天顶角余弦的增加而减小；随着观察者和太阳方位角差的增加而增加；随着高度的增加而减小；随着水平能见度的增加而增加；随着单次散射反照率的增加而减小。     

Interior radiances in optically deep absorbing media—III. Scattering from haze L

The interior radiances are calculated within an optically deep absorbing medium scattering according to the Haze L phase function. The dependence on the solar zenith angle, the single scattering albedo, and the optical depth within the medium is calculated by the matrix operator method. The development of the asymptotic angular distribution of the radiance in the diffusion region is illustrated through a number of examples; it depends only on the single scattering albedo and on the phase function for single scattering. The exact values of the radiance in the diffusion region are compared with values calculated from the approximate equations proposed by Van de Hulst. The variation of the radiance near the lower boundary of an optically thick medium is illustrated with examples. The attenuation length is calculated for various single scattering albedos and compared with the corresponding values for Rayleigh scattering. The ratio of the upward to the downward flux is found to be remarkably constant within the medium. The heating rate is calculated and found to have a maximum value at an optical depth of two within a Haze L layer when the sun is at the zenith. The location of this maximum moves toward the top of the haze layer as the solar zenith angle increases and also as the single scattering albedo decreases. When the single scattering albedo is less than 0·8, the downward flux is so small within the diffusion region that experimental measurements are probably not possible.     

The use of two angle elastic and Raman scattering to obtain molecular density and aerosol scattering profiles

The method of dual angle, multiple wavelength lidar interrogation to effect a radiative separation of the scattering produced by aerosols and molecules is extended. A given wavelength is transmitted, and the Raman shifted return from nitrogen as well as the elastically scattered transmitted wavelength are both interrogated. This procedure is carried out in the backscatter mode at the zenith and one other slant path at some angle from the zenith. The methodology is developed for obtaining molecular density, temperature, pressure, and aerosol scattering profiles.     

气溶胶凝聚粒子散射特性的数值计算

利用Cluster-cluster aggregation (CCA)模型,模拟了由相同数目球形原始微粒凝聚而成的四种随机取向气溶胶凝聚粒子．根据物质的电结构,将气溶胶凝聚粒子离散为一系列偶极子,结合离散偶极子近似方法,在获得每一个偶极子的电偶极矩之后,数值计算了气溶胶凝聚粒子散射强度的角分布,并分析了散射强度随入射光入射角度和气溶胶凝聚粒子尺寸参数变化的规律．结果显示：当散射角较小时,气溶胶凝聚粒子取向和入射光的入射角度对散射强度影响不大,当散射角增大时,散射强度则明显依赖于气溶胶凝聚粒子取向和入射光的入射角度;对于不同尺寸参数的气溶胶凝聚粒子,在同一角度入射情况下,随尺寸参数的增加,气溶胶凝聚粒子的散射主要集中于前向散射．     

椭圆柱体对任意入射极化的电磁波的散射

基于电磁场的多尺度变换理论,得到了以导体椭圆柱为例的电磁波任意极化,任意垂直入射到目标上的散射场的解析式.将所得结果应用于计算圆柱目标的散射场,结果与文献完全一致.对椭圆柱体的散射宽度随入射波方位角,电磁波频率以及目标尺寸的变化进行了仿真.结果表明,在垂直于电磁波的方向上观测时,椭圆柱的垂直尺寸对散射有较大的影响,电磁波水平极化时散射最强.所用算法适用于介质椭圆柱等目标的散射特性研究,所得结果为目标尺寸、形状遥感电磁测量等实际应用提供了理论依据.     

Symmetry relations revealed in Mueller matrix hemispherical maps

The hemispherical Mueller matrix map for light reflected from a plane-parallel planetary atmosphere is shown to obey several symmetry properties that provide a straightforward method to check their physical realizability. The mirror scattering relation and the reciprocity relation are employed to support the symmetry rules for hemispherical Mueller matrix maps. Additionally, two classes of experiments are identified in which the symmetry rules can be applied, namely, when the incident beam is at zenith and off-zenith angles and the scattering particles are spheres and randomly oriented hexagonal particles.     

黑松冠层反射光谱方向特征分析

松萎蔫病是松属树种的一种毁灭性病害，小范围甚至单木水平的森林病虫害的早期诊断对森林资源保护与可持续发展尤为重要。以感染松萎蔫病的黑松为研究对象，通过采集不同感病时期的黑松冠层的多角度光谱数据，分析不同特征波段的方向反射特征，总结不同感病程度黑松的冠层特征波段反射率的变化规律。结果显示：(1）在俯视观测时，在主平面方向的后向散射方向的反射率大于前向散射方向的反射率，并且在后向散射方向，四个波段的四个感病时期约在40°的观测天顶角出现热点效应；无论在主平面还是主垂面，蓝光波段（450 nm）与近红外波段（810 nm）的黑松冠层0°天顶角反射率呈现出感病初期＞健康＞感病中期＞感病末期的变化规律，红光波段（680 nm）和绿光波段（560 nm）的黑松冠层0°天顶角反射率呈现出健康≈感病初期＞感病中期≈感病末期的变化规律。在所有方位角，冠层反射率随着观测天顶角的增加而增大。(2）在仰视观测时，在主平面方向的后向散射方向的反射率小于前向散射方向的反射率，并且在方位角为0°时，4个波段反射率都是较大的；无论在主平面还是主垂面，蓝光波段（450 nm）绿光波段（560 nm）和红光波段（680 nm）的冠层反射率的大小呈现出感病初期＞健康>感病末期>感病中期的变化规律，近红外波段（810 nm）冠层反射率的大小呈现出感病初期＞健康>感病中期>感病末期的变化规律；在所有方位角，冠层反射率随着观测仰角的增加而减小。(3）黑松冠层反射光谱在俯视和仰视观测时，各个特征波段的二向性反射率的各向异性最强的是主平面，最弱的是主垂面，且主垂面的前向和后向反射率会呈现对称性，即“镜面反射”；各个特征波段在感病末期，黑松冠层反射率随观测天顶角的变化幅度较大，其他几个时期反射率随观测天顶角的变化幅度不明显。研究结果显示的树冠的不同角度的波段反射方向性特征为以后不同尺度的无人机监测的准确性与可靠性奠定基础，也为发展近地面便携式森林病虫害实时监测系统打下了基础。     

表面粗糙度对黑云斜长片麻岩不同探测角偏振度波谱影响研究

以黑云斜长片麻岩为例,探讨了表面粗糙度因子在350～2 500nm波段对岩石不同天顶角及方位角偏振度探测的影响,并在特征波段进行了定量分析。表明不同粗糙度的岩石表面,入射天顶角一定时,在镜面反射方位,偏振度随探测天顶角先是上升,到达最高值后又开始下降。(520±10)nm波段的偏振度在探测天顶角方向达到的最大峰值与表面粗糙度进行相关分析,发现他们呈幂函数关系。回归方程为:y=0.604x-0.297,可决系数R2为0.985 4。峰值所在天顶角度与表面粗糙度相关模型为,y=3.419 4x+51.584,y<90°,模型可决系数R2为0.817 7。偏振度随探测方位角变化的规律为以180°方位时偏振度最大,向两侧随探测方位离180°越远逐渐越低,并趋于0。(520±10)nm波段的偏振度在探测方位角180°方向达到的最大峰值与表面粗糙度进行相关分析,发现他们呈幂函数关系。回归方程为:y=0.582 2x-0.333,可决系数R2为0.984 3。对以上回归模型进行F检验,发现偏振度峰值及所对应角度与粗糙度之间存在显著的相关关系。     

温室番茄缺素叶片偏振反射特征分析

为提高番茄植株营养胁迫定量分析模型的精度,探究偏振检测在植物单叶尺度进行无损检测的优势,利用自行研制的偏振反射光谱系统检测不同生长期温室番茄缺素叶片偏振反射特征。对影响番茄单叶偏振反射的主要因素：方位角、入射天顶角、探测天顶角、光源偏振片起偏角度、探测器偏振片起偏角度进行了讨论,通过正交试验的极差分析获取光谱仪各测量角度参数的优水平,并通过实验进一步验证,最终分析得到偏振光谱系统检测番茄缺素叶片的角度组合及主次排序为：入射天顶角60°、光源起偏角度0°、探测器起偏角度45°、探测天顶角45°、方位角180°,在此基础上对不同生长期的缺氮、缺磷、缺钾叶片以及不同缺素程度的叶片进行分析比较,结果显示偏振反射比随番茄叶片的生长周期呈现正相关关系,缺素和营养过量均能导致偏振反射比的下降,偏振反射比在结果期和采收期的降幅较为明显。对于偏振反射光谱在植物单叶尺度营养快速检测的深入研究具有一定的理论和实践意义。     

Scattering of an electromagnetic wave from a slightly random dielectric surface: Yoneda peak and Brewster angle in incoherent scattering

Abstract

The scattering of an electromagnetic wave from a two-dimensional, slightly rough dielectric surface is studied based on the stochastic functional approach. It is shown that in the case of TM(p)-polarized incidence there exists a zero in the incoherent scattering at the angle we call the ‘Brewster scattering angle’, which depends on the incident angle in contrast to the Brewster angle of coherent reflection which is independent of the incident angle, that a ‘quasi-anomalous scattering’ can generally occur in the optically denser medium at the critical angle of total reflection in both TE(s)- and TM(p)-polarized incidence, regardless of which side of the random surface is illuminated, and that the Yoneda peak in the x-ray scattering can be interpreted as a special case of the quasi-anomalous scattering which becomes sharper when the relative refractive index becomes closer to unity as in the x-ray region. Cross-polarized scattering and enhanced backscattering due to the second-order effect are also calculated.     

A fast estimation of sonar cross section of acoustically large and complex underwater targets using a deterministic scattering center model

In this paper, a fast method is proposed to estimate the sonar cross section of acoustically large and complex underwater targets such as submarines and torpedoes. The proposed method is based on a deterministic scattering center model which constructs scattering center database by using a combining method of physical optics and geometric optics and then reconstructs sonar cross section patterns from that database with a polynomial interpolation with respect to the incident angle. The parametric studies to find appropriate intervals of the reference incident angle are systematically carried out for simple targets such as a flat square plate and an orthogonal dihedral. Moreover, to validate the proposed method, sonar cross sections of real-like targets such as a pressure hull and an idealized submarine are calculated. The comparisons show that the results by the proposed method are in good agreement with those by the direct calculation.     

Angle step selection for geometrical-optics approximation in light scattering

On the basis of the Shannon sampling theorem, we present a relationship between the maximal scattering angle step and the radius of particles in the calculation of light scattering intensity distribution. For the first rainbow intensity application, the relationship between the maximal scattering angle step and radius of particles is derived from that between the ripple frequency and radius and refractive index of particles using this method. For the geometrical-optics approximation, the incident angle is used to calculate the scattering intensity distribution. To get the highest speed, the maximal incident angle step is necessary. The relationship between the maximal step of incident angle and radius of particles is deduced from the maximal scattering angle step equation. As indicated by our result, the maximal step of the incident angle is not a constant and it varies with incident angle.     

超光滑基片表面散射的数值研究

以一阶微分散射理论为基础,从理论和模拟两个方面对超光滑基片表面的散射电磁场进行了数值研究.分析了s偏振光和p偏振光的微分散射随入射角和散射角的分布情况.研究发现,当入射角较大时,p偏振光在某个散射方向的微分散射为0,而无论入射角和散射角如何变化,s偏振光的微分散射均大于0.当用光散射法对超光滑基片进行表面测试时,相对于...     

冬小麦冠层光谱的方向性特征分析

二向性反射因入射和观测的角度变化而变化,合理选择遥感观测角度、太阳天顶角等为提高遥感应用精度提供可能。通过采用各向异性因子和各向异性指数定量分析了冬小麦冠层窄波段二向性反射率及NDVI的方向性特征。分析结果表明：主平面内二向性反射率的各向异性最强,垂直主平面最弱,其他平面介于前两者之间;可见光波段反射率随观测天顶角的敏感性大于近红外波段;反射率对太阳天顶角的敏感性随着观测天顶角的增大而增大。前向NDVI整体上大于后向,且NDVI随着太阳天顶角的增大呈增大趋势。为了减少观测方式所带来的不确定性,应尽量选择近红外波段和小太阳天顶角,估算结构参数时应尽量选择主平面进行遥感观测,在利用NDVI估算生物物理参数时尽量远离“热点”区域。     

沙丘粗糙面的二次极化电磁散射

研究了新月形沙丘粗糙面的二次极化电磁散射. 结合射线追踪理论, 由一次散射面元的反射场照射到二次散射面元, 采用基尔霍夫近似推导了二次散射面元的二次极化散射场. 计算结果表明二次极化散射结果在特定的角度和类型范围内有显著影响. 在电磁波射向背风坡时可以发现其同极化散射截面在入射角较大时大于其他入射方向的结果, 入射角在休止角附近时的交叉极化散射截面出现峰值, 以及前后狭长沙丘之间的二次极化散射特别突出. 本文结果可用于反演分析沙漠地区的风场信息. 关键词： 新月形沙丘 二次极化散射 射线追踪 休止角