水下目标圆偏振成像及最远 成像距离的计算

报道了用圆偏振技术进行水下目标成像结果并分析了用圆偏振技术提高图像清晰度的原因:推导了水下目标最远成像距离的计算公式,在衰减常数α为0.5的水体中,目标放在1.5m处,测量出用圆偏振成像系统成像所得图像对比度C为4.1,通过r0和C可计算出圆偏振成像系统的最远成像距离r为1.92m,与实测距离相差0.08m,相对误差为4%。     

红外偏振成像下的弱小目标检测

为了验证红外偏振成像在海杂波中检测弱小目标的可行性,开展了海背景下的红外偏振成像实验。使用未装偏振片和加装偏振片的红外热像仪对海杂波背景下的弱小目标进行了探测,同时采集了相应状态下的数据。为了验证偏振片对海杂波的抑制效果,对采集的数据进行了图像处理。从没有加装偏振片的红外热像仪数据中无法提取测试目标,而从加装偏振片后的红外图像数据中通过图像增强、中值滤波以及边缘检测的图像处理手段提取出了测试目标。     

偏振成像技术的进展

介绍了截至2013年偏振成像技术的研究进展。总结了偏振成像技术的主要研究内容。分别介绍了偏振成像技术方案分类,红外偏振成像仪和偏振焦平面探测器,偏振成像试验,以及偏振光线追迹的最新研究进展。     

一种单幅图像去雾方法

针对雾天图像时比度差、能见度降低的特点,提出了一种局部尘雾消除方法--LDOS.首先引入暗原色统计先验,说明有雾图像暗通道和其尘雾浓度图之间的近似关系.然后,针对以往的尘雾浓度估计方法存在估计结果粗糙、修正方法复杂、不易实现等问题,给出了一种新颖而有效的估计方法--中值滤波.该方法既能平滑尘雾浓度图,又能很好地保留场景...     

基于偏振成像和图像融合的目标识别技术

提出了一种基于偏振特征的目标识别技术.实验采用He-Ne激光作为照明光源,根据目标散射光偏振度的差异,利用DSP图像采集系统获取了目标的偏振图像,并利用图像融合技术计算了目标的Stokes图像和偏振度图像.结果显示:偏振成像有效地滤除了杂乱背景散射光的影响,明显提高了目标成像的对比度和分辨率.所以偏振成像技术可以有效地提高目标探测和识别效率.     

一种基于图割的图像去雾方法

暗原色先验去雾方法在户外场景图像去雾方面取得了一定的去雾效果,但该方法在估计近景局部高亮物体透射率时会产生严重误差。本文针对暗原色先验方法的不足首先利用图割理论对粗透射率图进行分块,并使用指导滤波器对细化透射率图进行校正,最后将校正的透射率图带入有雾图像成像模型求得清晰无雾图像。通过将基于暗原色先验的方法、局部对比度最大化的方法和本文中的改进方法进行了实验并对实验结果进行了分析,结果表明本文中的图割分块校正透射率的方法能够更有效地复原因雾霾影响的单幅降质图像。     

圆偏振光偏振复用激光通讯系统

提出了一种采用圆偏振光的偏振复用通讯系统。其基本设想是信号光在空间中以左 旋和右旋圆偏振光的形式进行传播,在接收端将这两种偏振光区分并分别接收。本文详细论证了在两个相对运动点之间采用圆偏振光实现偏振复用激光通讯的可行性。     

伪装遮障的光学与红外偏振成像

为了研究伪装遮障对抗偏振遥感的侦察效果,采用多波段偏振CCD相机在光学与红外波段获得伪装遮障的偏振图像,并提取其中的偏振信息.研究发现:在表面形态一定的情况下,伪装遮障散射光的偏振信息受光线入射角和表面反射率的影响较大.偏振信息对遮障的表面粗糙度和空间结构非常敏感,可以增强图像中目标与背景的对比度,提高识别准确率.伪装遮障和自然背景的散射光偏振度和偏振角信息有较大差别,因而,根据偏振信息成像可以有效地识别出图像中的伪装遮障,偏振成像在伪装目标识别方面具有重要的军事应用价值.     

红外偏振成像在伪装目标识别中的应用研究

红外偏振成像技术可以提高探测伪装或隐身目标的能力。作为对抗红外隐身的侦察手段,它已成为国内外研究的重要内容。通过分析红外偏振成像的进展,提出将红外偏振成像技术应用于目标检测。为了研究伪装目标的偏振散射特征,利用红外偏振成像系统对覆盖和未覆盖军用三色迷彩伪装网的目标场景进行了探测研究。研究发现,红外偏振成像可以作为探测伪装或隐身目标的新途径,其成像效果较好。此外还证明偏振探测技术对复杂背景中低反射率伪装目标的独特识别优势在中红外波段同样成立,而且偏振角成像对伪装网的外形特征非常敏感。     

一种基于反馈机制的闭环图像去雾算法

针对目前去雾算法易受大气环境随机性和复杂性影响而造成自适应性不强的问题,该文提出一种具有反馈机制的自适应闭环去雾算法。该算法首先通过基于人眼视觉的特征认知评价进行参数初始化;然后利用去雾强度评价结果对反馈校正局部对比度参数进行调节,从而对去除加性光照后的图像进行自适应局部对比度提升;最后借鉴去雾后图像的自然度设定迭代终止条件,决定是否输出去雾结果。实验表明该算法能够自适应提升不同退化类型、不同退化程度下的雾天图像对比度,且去雾结果的信息熵和清晰度质量评价指标优于已有算法。     

Self-powered circularly polarized light detector based on asymmetric chiral metamaterials

Circularly polarized light (CPL) has been given great attention because of its extensive application. While several devices for CPL detection have been studied, their performance is affected by the magnitude of photocurrent. In this paper, a self-powered photodetector based on hot electrons in chiral metamaterials is proposed and optimized. CPL can be distinguished by the direction of photocurrent without external bias owing to the interdigital electrodes with asymmetric chiral metamaterials. Distinguished by the direction of photocurrent, the device can easily detect the rotation direction of the CPL electric field, even if it only has a very weak responsivity. The responsivity of the proposed detector is near 1.9 mA/W at the wavelength of 1322 nm, which is enough to distinguish CPL. The detector we proposed has the potential for application in optical communication.     

一种新型的圆偏振光分束器的设计及分析

对两种旋向相反却又各向同性的旋光晶体进行组合,可以获得一种新型的圆偏振光分束器。本文计算了波长为300nm-800nm的偏振光通过此类器件后产生的左右旋圆偏振光的分离角,并对其相关的性能进行了分析。计算结果表明:对于两块晶体所组成的器件,左右旋圆偏振光之间分离的最大角度超过0.2°。此类器件的特点是由各向同性的旋光晶体构成,光在其内部传输时,具有的圆偏振状态不会因传输方向而变,经过器件后的左右旋圆偏振光都是严格的圆偏振光。     

红外圆偏振光透雾性能分析

雾对红外系统的探测性能有一定影响,圆偏振光在雾中传输时具有优良的保偏性和持久性,为解决雾的红外遮蔽问题提供了新思路。分析雾对红外光波的衰减是由吸收和散射共同作用;阐述了圆偏振光透雾是由圆偏振光波螺旋性的随机化速率缓慢和圆偏振光子在传播方向的随机化速率缓慢共同作用,致使圆偏振光受雾滴的光散射影响较小;结合圆偏振透雾机理和大气光谱特征,探究雾中目标检测的优化波段,研究表明:在近红外波段的0.78~1.1 m、1.48~1.56 m、1.63~1.86 m、2.03~2.18 m、2.39~2.5 m和中红外波段的3.6~4.15 m,适宜采用圆偏振成像技术提高红外系统透雾性能,长红外波段,雾滴的光吸收占总消光的比例增大,已不宜采用圆偏振成像技术来提高红外系统的透雾性能。最后,分析了红外圆偏振透雾技术的特点,并对深入研究提出了建议。     

一种具有谐波抑制功能的圆极化天线设计

微波能量传输以及无线通信系统中的天线设计,追求剖面低、质量轻,易与平面电路集成。基于此,设计了一种具有谐波抑制功能的单馈背腔圆极化环缝天线。该天线工作在5.8 GHz,采用导波结构基片集成波导(SIW)抑制表面波,提高了天线增益。SIW通过2排金属孔阵列集成在介质板上,在介质板上蚀刻短路圆环缝隙,辐射电磁波。采用50 Ω微带线到SIW过渡的背馈方式,并在馈线上引入并联枝节,有效抑制了高次谐波,且实现了基于基片集成波导天线的谐波抑制。通过加工测试,天线的轴比为0.67 dB,增益为6.9 dBi,阻抗匹配良好,前后比为22 dB,仿真结果与实测结果吻合良好。     

基于人工阻抗表面的毫米波圆极化全息天线

基于全息光学原理,提出并设计了一种加载相位调制的毫米波圆极化全息天线,天线由电小尺寸的人工阻抗单元按表面阻抗分布参数排列而成。利用横向谐振技术分析了标量人工阻抗单元表面阻抗的计算方法,建立了单元尺寸与表面阻抗之间的数据库。给出了干涉表面的阻抗分布参数计算方法,通过加载相位调制,实现了全息天线的圆极化。利用Matlab-HFSS联合建模仿真,建立了毫米波圆极化全息天线的基本模型,仿真结果表明,天线工作于35 GHz,波束沿法向偏转35°,中心的轴比小于1.5 d B。     

Dual-frequency circularly polarized antennas based on stacked monofilar square spirals

Two radiating spirals stacked on a foam substrate are used in the design of a circularly polarized antenna designed to respect new bandwidth constraints resulting from the emergence of multimedia services in satellite communications. Orthogonal circular polarizations are required for up and down links over large frequency bandwidths. In the single antenna, 4 to 5% axial ratio (AR) bandwidths are observed in a large beamwidth for both bands. This AR bandwidth increases appreciably (24 to 31%) when two antennas are combined in a sequentially rotated configuration.     

A circularly polarized rectangular microstrip antenna usingsingle-fed proximity-coupled method

A new circularly polarized rectangular microstrip antenna using a proximity-coupled feed method is proposed in this paper. This antenna is fed by a microstrip line offset from the center of a rectangular microstrip antenna. The proposed antenna has no 90-degree hybrid coupler for circular polarization and allows easy connection between a microstrip line and an antenna element. The measured results verify the circular polarization and show that good return loss and axial ratio characteristics have been obtained     

一种基于正交线偏振光的高精度方位测量方法

为了解决传统基于正弦波磁光调制的方位测量方法 存在小角度精确测量时信号微弱、处理难度大等问题,提出了一种基于正交线偏振光磁光调 制的方位精 确测量方法。首先简单阐述了传统方位测量原理,分析了小角度范围内测量时信 号微弱的根本原因;其次提出了改进的方位测量方法,在阐述测量装置结构原理 的基础上,建立了基于磁光调制后两束正交线偏振光的光强模型,通过分析发现 两路调制后混合信号中交流信号的极值点信息均与方位角相关,且同一位置对应 的极值点信息具有相位相反的特性,采用二者相减的方式增强了有用信号的幅 值,提高了数据采集精度。仿真结果表明,通过各种情况下与传统方法中参与方 位角计算的信号幅值对比,文中提出的方法能够明显增强信号幅值,利于提高数 据采集精度和方位测量精度。     

Research on circularly polarized conical-beam antennas

This antenna is intended for communication between a stationary satellite and mobile stations, and is designed to possess circularly polarized conical beams. It generates a beam in the desired direction, by means of changing the inclination angle of the linear-antenna elements, and the spacing between the antenna elements, without phase shifters. The antenna inclination angle (α), the antenna length (e), the distance between antenna elements (d), and the radius of the circular reflector (R), are adopted as parameters, and optimum values for the directivity of the research objective are obtained by calculation. Four elements of the antenna are fed by in-phase signals, the distances between elements are set to appropriate lengths, and by providing spatial phase differences of 90°, circularly polarized waves are obtained. The antenna elements are fundamentally monopole radiators. Ultimately, the antenna parameters were determined as follows: ℒ=0.64λ (120 mm), R=0.43λ (80 mm), α=45°, and d=0.48λ (90 mm). In the calculation, the frequency was set to 1.6 GHz. It was seen that the beam radiation intensity took the maximum value in the angular range of &thetas;=30° to 60°, and that the &thetas; and φ components of the electric field were approximately equal. In other words, the radiated waves were circularly polarized. An experiment for measuring the directivity of the circularly polarized conical-beam antenna was carried out by using four monopole antennas, and the effectiveness of the theoretical analysis was confirmed. Experiments were carried out for the impedance and directivity     

Operation of a circularly polarized ring laser

Although there has been a large amount of experimental work published on the operation of the ring laser, nearly all of it was concerned with lasers operating in linearly polarized modes. In this paper the operation of a ring laser using the 1.153-μm wavelength transition of the He-Ne mixture in a cavity with no polarization constraint is reported. It was found that the two traveling waves operated in the same sense as circularly polarized modes and that there was no measurable coupling between the traveling waves via the amplifying medium, although there was still locking induced by coupling through cavity imperfections.