地面目标的中波红外高光谱成像特性测量

利用Telops公司设计的Hyper-Cam中波高光谱成像仪对水泥地上某坦克模型进行3~5μm波段的红外高光谱成像测量。对实验数据进行了逐像素点的大气校正。基于矫正后的实验数据,分析了仪器误差、随机误差、大气校正传递误差等对测试不确定度的影响。分析了该坦克模型在不同谱段上的亮度分布和模型上不同部位的光谱分布特性。结果表明:在波数为2000~3000 cm-1波段,其相对不确定度一直稳定在10%以内,但是在大于3000 cm-1的波段,其误差迅速上升,主要因为常温物体的中波辐射低,在该波段目标辐射与大气路程辐射接近,而引起的噪声增大,造成的测试信噪比降低。该坦克模型光谱辐射亮度测试数据的平均相对不确定度在20%以内,整体误差较低。光谱分布上,坦克各部分特征点和水泥地表的光谱辐射亮度在波长为4.2~5μm波段时的差异性比波长为3.0~4.2μm波段时的差异性更大,且探测器接收到的4.2~5μm波段的光谱辐射亮度要大于3.0~4.2μm的光谱辐射亮度。由于4.3μm波段处于大气吸收带,大气透射率几乎为0,以至于无法获得目标的光谱辐射亮度的真实测量值。空间分布上,模型的辐射亮度主要集中在侧边涂层上,炮口处和履带处的辐射亮度较小。目标各部位辐射亮度分布与周边水泥地表的辐射亮度有着明显差异性。在3~5μm的辐射亮度中,4.4~4.8μm波段的辐射亮度占比较高,该波段成像效果最好。3.2~3.8μm波段的辐射亮度占比较低,该波段成像效果较差。处于大气吸收带的4.2~4.4μm波段,由于大气透射率几乎为0,无法获得其准确的空间辐射亮度分布。研究表明该拓展中波高光谱成像仪在地面目标的中波红外高光谱成像特性研究上具有目标区分精确、误差小、“图像光谱合一”的特点,测试数据可以应用于目标的红外高光谱隐身设计、目标的分类与识别等领域。

光学介质薄膜表面冗余节瘤粒子的散射角分布

采用时域有限差分法研究了多因素对光学介质薄膜表面冗余节瘤粒子微分散射截面随散射角的变化规律.对光学介质薄膜表面冗余节瘤粒子复合散射进行建模,并针对典型半空间问题,对总散射场进行分解并对相应的场相位进行求解,给出网格剖分规则.将数值结果退化为冗余球体粒子,与MOM (Method of Moments)矩量法进行详细比较,验证程序的有效性.分析P偏振光入射下,入射角、长短轴轴比和镶嵌高度h对Cu和SiO_2镶嵌粒子微分散射截面随散射角的影响规律.结果表明:微分散射截面的最大峰值出现在入射角的镜面值角度;在镜向散射区域附近,对于扁平回转椭球体粒子微分散射截面随冗余节瘤粒子轴比的增大而减小,扁长回转椭球粒子的规律相反;在[-90°,-60°]散射角区域,微分散射截面与冗余节瘤粒子镶嵌高度成正比,镶嵌高度对介质粒子散射特性影响更大.

各向异性半椭圆型波导对平面波的电磁散射

讨论了横截面为半椭圆型各向异性介质柱体波导嵌入到导体时对平面波的电磁散射.散射场和柱体内场均表示为椭圆柱坐标系下的马丢函数级数展开式,其中的待定系数通过边界条件进行确定.利用积分方法解决了马丢函数在边界条件下无法满足正交关系的事实.为描述问题的方便,仅讨论了横磁波(TM)情形,推导出横电波模式.最后给出了几种不同参数的数值结果.

微粗糙光学表面与多个镶嵌粒子差值散射场特性

本文基于时域有限差分算法,研究了微粗糙光学表面与多个镶嵌粒子的差值场光散射问题。将光学基片视为微粗糙光学表面,利用蒙特卡洛方法解决了光学表面存在粗糙度的问题,并将差值场散射理论加入到计算模型中,更好地分析了缺陷粒子的散射特性,将计算区域划分成上下两个半空间,建立了微粗糙光学表面与镶嵌多体粒子复合散射模型,并与矩量法计算结果比较验证了理论的有效性。运用此模型分析了入射角、镶嵌粒子尺寸、粒子间距、粒子个数等物性特征对微粗糙光学表面与镶嵌多体粒子差值散射场的影响。实验结果表明:在一定激光入射角下,以相同回波探测角度间距20°对光学表面进行测量能够有效地检测出缺陷粒子。本文结果为光学无损检测、光学薄膜、微纳米结构的光学性能设计等提供了理论依据和技术支持。

An Adaptive Objective Function for Evaporation Duct Estimations from Radar Sea Echo

In the process of atmospheric refractivity estimation from radar sea echo,the objective function that calculates the match between the predicted and observed field plays an important role.To reduce the effect of noises from long ranges on the objective function,we present a selection method of final ranges for inversion.An adaptive objective function is introduced with a linear distance weight added to the least squares error function(LSEF).Through an evaporation duct height(EDH)retrieving process,the performance of the adaptive objective function is evaluated.The result illustrates that the present method performs better than the LSEF in EDH inversions from clutters with different clutter-to-noise ratios.

Modification of Classical SPM for Slightly Rough Surface Scattering with Low Grazing Angle Incidence

Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classical perturbation method at grazing angle is overcome for the vertical polarization at a rough Neumann boundary of infinite extent. The derivation of the formulae and the numerical results show that the backscattering cross section depends on the grazing angle to the fourth power for both Neumann and Dirichlet boundary conditions with low grazing angle incidence. Our results can reduce to that of the classical small perturbation method by neglecting the Neumann and Dirichlet boundary conditions.

A Modified Perturbation Method of Electromagnetic Scattering from a Rough Surface by Considering the Effect of the Curvature

A modified perturbation method of electromagnetic scattering from a rough surface is presented,in which the effect of the curvature of the surface is taken into account based on the conventional small perturbation method.The problem of scattering error by the conventional small perturbation method at grazing angle is solved.Compared with a set of measured data,the numerical results of the backscattering radar cross section show that this modified perturbation method is validity for small,moderate and grazing angle incidence.

Fractal Linear Arrays

The general expression of the fractal linear array factors is derived.The similarity of the patterns and their fractal features are examined.The relation between the maximum side-lobe and the fractal dimension is shown.

A Phase-Perturbation Technique for Light Scattering from Randomly Dielectric Rough Surfaces

With the theory of rough surfaces scattering,a numerical formula for calculating the bistatic and backscattering radar cross section from randomly dielectric rough surfaces is derived by using phase-perturbation technique.The backscattering laser radar cross sections per unit of some rough samples are computed at λ=1.06μm.The numerical results are in good agreement with experimental data.