地面目标动态红外特征模拟与隐身技术的研究

针对易受敌方红外制导武器攻击的地面军事目标,模拟并计算出其红外辐射特征。通过合理的假设,将复杂的三维辐射与对流耦合传热问题简化为一维瞬态传热问题,运用多层有限差分的数值计算方法计算模拟出目标瞬时温度变化方向图,得出其动态红外特征。在此基础之上,分别研究了地面目标不同部位(顶部与侧面)隐身所需要的表面发射率与温差的关系。分析了在不同温差条件下目标隐身所需表面发射率随时间的变化关系。计算模拟得出目标与背景在一日之中都存在明显的温差,最大温差可达10℃左右。分析得出利用水雾隐身使目标与背景的温差控制在2℃以内可达到良好的隐身效果。     

红外小目标与背景辐射对比度的研究

红外目标与背景的对比度特征是红外探测系统检测的重要特征。研究了目标和背景在探测器上的辐射照度,提出了一种红外小目标与背景的辐射对比度,分析了该目标与背景对比度的相关因素。     

红外伪装涂料发射率的季节性要求

为了研究伪装涂料8～14 μm波段的平均发射率在不同季节的取值范围,结合太阳辐射,植被温度以及气温的一日变化,建立目标及单一植被背景在晴朗天气情况下不同季节的一日辐射温度变化模型.以合肥地区为例,分别以春分、夏至、秋分、冬至四个节气的日气候状况代表春夏秋冬四季的气候特征,采集该地区在四个节气近五年的日值气侯数据,对覆盖不同发射率伪装涂料的目标以及植被背景在四个节气中从6时到22时的辐射温度变化进行模拟.获得目标和植被背景的日辐射温度变化数据,计算不同覆盖发射率值的伪装涂层时的目标和背景的欧氏距离和伪装效率.利用欧氏距离和伪装效率对目标的伪装效果进行分析.当欧氏距离最小时目标与植被背景红外特征最接近,春夏秋冬欧氏距离最小时的发射率值依次为0.58、0.33、0.41、0.86;以参考目标与背景的辐射温度差控制在4K以内为实现隐身的标准,春夏秋冬伪装效率最高时的发射率值依次为0.6、0.3、0.4、0.9.     

室温下低温背景红外场景生成方法实验研究

针对高空红外场景模拟的需要,提出了模拟低温背景红外场景的新物理概念和半实物仿真实验装置.将锗单晶制作的初始透明的半导体屏放置于低温系统前端,通过控制其小于禁带宽度的局部辐射系数,在室温下(≥27℃)得到低温背景(≥-30℃)的红外场景.对液氮槽和半导体致冷器生成的冷背景的效果、辐射功率差随写入光功率的变化及低温背景和目标的温度对比度进行了实验测试.实验结果表明,液氮生成的冷背景可达-30℃,半导体致冷器为3℃;在一定范围内增大写入光的功率可以提高半导体屏的转换效率,写入光功率过高会造成辐射功率值的饱和;随着写入光功率的增加,温度对比度也大幅升高.     

低温红外辐射源研究

随着空间红外探测、卫星遥感等技术的飞速发展,低温红外辐射源的需求日益迫切。研制了一种基于液体循环控温原理的低温红外辐射源。辐射源的工作温度范围为-60℃～50 ℃,控温精度达到0.01 ℃,有效发射率优于0.999 7。首先阐述了低温红外辐射源的设计原理,介绍了辐射源腔形设计,使用基于蒙特卡罗算法的软件STEEP3计算了辐射腔的有效发射率;接着对辐射腔内部温度特性进行了研究,实验结果表明低温红外辐射源辐射腔温度均匀性优于0.02 ℃,腔底温度稳定性优于0.05 ℃/h;最后通过与镓熔点黑体比较得到低温红外辐射源在29.76 ℃时的光谱发射率,与仿真计算结果一致。     

基于相关性的中红外温度与发射率分离算法

温度和发射率是耦合在一起的.在精确获得大气参数的情况下,由传感器的辐射测量反演地表的温度与发射率,仍然是一个病态问题,必须采取一定的策略进行温度与发射率的分离.因此,温度与发射率的分离是红外遥感的核心问题.文章在分析无太阳直射光影响时大气下行辐射和含有大气残留的地表发射率之间关系的基础上,提出了一个针对野外测量中红外高光谱数据的温度与发射率分离算法.该算法利用大气下行辐射和含有大气残留的地表发射率之间的相关性作为判据来优化地表温度,进而获得地表发射率.基于模拟的中红外高光谱数据,对算法的精度进行评价.结果表明,该算法能够获得较高的地表温度和发射率反演精度;具有较广的适用范围,对测量过程中大气下行辐射变化不敏感;同时算法具有一定的抗噪性.     

红外烟幕遮蔽率及其分布表征方法

目标与背景的辐射对比度是红外系统探测目标的主要依据,也是烟幕干扰重点降低的一个参量。结合辐射对比度的定义和红外定标原理,由目标和背景的视在辐射亮度引入其视在辐射对比度,并与目标和背景热像图的灰度值关联起来。利用烟幕遮蔽前后与目标和背景视在辐射对比度变化相对应的热像灰度对比度的变化,对烟幕遮蔽率进行表征。用提出的背景灰度方法对干扰实验结果进行了表征,计算得到3组试验的背景灰度值分别为91.902 4、88.002 0、33.285 6,并获得了目标区域各像元遮蔽率的直观分布图,克服了以往以点代面的评价方法。     

基于光子晶体的热红外迷彩

低发射率光子晶体(PC)具有高反射特性,在高温环境的强烈照射下,高反射光子晶体会成为亮目标。为了使光子晶体具有环境适应性,使之在相当宽的照度范围内都能与背景融合,对光子晶体的特性进行了深入研究。采用改变光子晶体周期数的方法,设计并制作了发射率分别为0.116、0.212、0.307、0.519、0.606、0.718的6种光子晶体,拼接成4块光子晶体迷彩(PCpp),并将其覆盖在仿真目标上。用8~14μm热像仪观察目标和背景,并记录各个时间点的平均辐射温度数据,利用辐射温度来计算目标和背景之间的欧式距离和目标在此背景下的伪装效率。对比结果发现,发射率为0.212、0.307和0.606的光子晶体迷彩在温度范围为292~302K的条件下,该光子晶体迷彩的平均温度与草地背景温度的欧式距离为12.55K,极限温差ΔT0为4K时的伪装效率为76.92%,能够使目标和背景很好地融合。     

固体材料定向光谱发射率测量装置研究及误差分析

针对红外隐身材料光谱发射率测评的需要,提出一种基于能量法的发射率测量模型,并建立起固体材料定向光谱发射率测量装置,能实现温度范围50℃～300℃与光谱范围1.3μm～14.5μm的固体材料定向光谱发射率测量。通过对试样进行实测,得到不同样品在150℃和同一样品在不同温度下的光谱发射率曲线,得出该材料发射率随温度变化的结论。最后分析了样品同黑体温度不等引起的误差,给出温差为1℃和2℃时,发射率相对误差随温度与波长的分布曲线,以及不同黑体温度下3μm～5μm和8μm～14μm的平均相对误差值。     

机载FTIR地球大气红外背景辐射光谱特征研究

介绍了机载傅里叶变换红外(FTIR)光谱仪测量地球大气红外背景辐射的实验过程,对地球/大气的红外背景辐射进行了详细的分析,给出了描述这一辐射过程的理论表达式,证明红外背景辐射主要取决于地表温度、地表发射率、大气透过率和大气温度这四个参数。在理论分析的基础上,对不同观测高度、不同地物背景的实测光谱进行了对比和分析,得到了红外背景辐射的光谱特征。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.     

Direction-of-arrival estimation using matrix spatial prefiltering approach

An approach to direction-of-arrival （DOA） estimation for multiple narrowband farfield signals is proposed. The technique uses a novel matrix spatial prefiltering approach. Specifically, a matrix filter is designed to spatially filter the incoming data snapshots. The un-wanted components arriving from the stopband angular sectors are attenuated and the desired components from the angular sector of interest pass with minimal distortion. The matrix filter spatially filters the element-space data and the output reserves the element-space data property, which makes it very useful by passing sensor data through a spatial prefilter prior to applying many other array processors to attenuate interferences and improve system performance. Several examples of DOA estimation problem are presented to illustrate the performance of the proposed spatial prefiltering approach. Results of simulation and real data show that the pre-filter can efficiently attenuate the spatial interferences and significantly improve the estimation and resolution capability of DOA estimators at low signal-to-noise ratios for the sources located inside the passband sector. In addition, the use of spatial prefilter makes it possible to estimate DOAs for multiple sources more than the number of the elements of an array.     

Quantum efficiency calibration of opto-electronic detector by means of correlated photons method

A new calibration method of detectors can be realized by using correlated photons generated in spontaneous parametric down-conversion (SPDC) effect of nonlinear crystal.An absolute calibration system of detector quantum efficiency is performed.And its principle and experimental setup are introduced.A continuouswave (CW) ultraviolet (351 nm),diode-pumped,frequency-doubled,and solid-state laser is used to pump BBO crystal.The quantum efficiencies of the photomultiplier at 633,702,and 789 nm are measured respectively.The coincidence peaks are observed using coincidence circuit.Some measurement factors including the filter bandwidth of trigger channel,the detector position alignment and polarization of the pump light are analyzed.The uncertainties of this calibration method are also analyzed,and the relative uncertainties of total calibration are less than 5.8%.The accuracy of this method could be improved in the future.