共查询到19条相似文献,搜索用时 908 毫秒
1.
《光学学报》2020,(3)
傅里叶变换是干涉图分析处理的常用方法,由于截断效应,对样本数据直接进行傅里叶变换时会发生频谱泄漏,常采用加切趾函数的方法减小泄漏。首先分析多种常见切趾函数的性能,研究切趾函数主瓣宽度与旁瓣衰减对频谱泄漏的影响;在此基础上,提出一种基于零阶贝塞尔函数加权的三角窗切趾函数,对三角窗函数加权,使其旁瓣衰减加快。实验结果表明:采用提出的改进的三角窗切趾函数能有效抑制频谱泄漏;相比于三角窗,改进的三角窗切趾函数平均峰-峰值信噪比提升了4.9%,方均根值信噪比提升了3.5%,优于常见窗中最优的布莱克曼窗。改进的三角窗切趾函数的主瓣宽度为0.043π,与汉宁窗接近,具有较高的频率分辨率。 相似文献
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空间预滤波加无约束自适应噪声抵消器构成了一种主瓣约束的自适应旁瓣抵消器。这种自适应旁瓣抵消器由于实现了保持主瓣方向以及主瓣形状的导数约束,具有较好的主瓣保持性能,且结构简单,便于工程实现。本文在原有理论研究的基础上,着重从实验方面研究这种自适应旁瓣抵消器的主瓣保持和旁瓣抵消性能。设计并构造了一个实验系统,该系统利用一种新的空间预滤波结构,使其更宜于工程实现。进行了水池和海上试验,详细考察了输入信噪比、信号干扰比、信号与干扰带宽和自适应步长因子等参数对系统性能的影响。取得的结果证实了理论分析的正确性。 相似文献
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针对线性调频信号同步相关的旁瓣、m序列扩频同步的序列自噪声和二进制相移键控调制信号在主瓣周围一个码片范围内存在较强烈的旁瓣三个问题,提出了一种基于二进制偏移载波(BOC)调制信号的无干扰窗水声同步方式.利用互补序列的非周期自相关函数之和为零的特殊性质,实现了在主瓣周围一个码片范围外,零相关窗范围内的无干扰窗.使用BOC(1,1)方式对信号进行亚载波调制,以减少主瓣周围一个码片范围内的旁瓣.对单通道信号和双通道信号的零相关窗形式都进行了设计,通过仿真和实验验证了BOC零相关窗方法在水声系统的同步、信道测量和估计中的有效性. 相似文献
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提出改进的粒子群优化算法,获得波束方向图主瓣宽度和旁瓣级折中的优化立体阵形,避免基本实数粒子群算法仅采用旁瓣级或主瓣宽度一个性能指标优化而导致另一个性能指标恶化的问题,利用阵列视角限制进一步优化立体阵形并设计了声成像测量系统。改进的粒子群算法与基本粒子群算法仿真优化阵形比较表明改进粒子群算法设计的优化阵形在保持较窄的主瓣宽度的条件下具有较低的旁瓣级。阵列声成像测量系统的性能测量分析结果表明该系统的空间分辨率和旁瓣抑制能力与理论结果接近,验证了所提算法的有效性。 相似文献
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基于傅里叶变换红外光谱仪干涉图的单边过零采样和非对称性,对相位校正技术进行研究和改进。针对Mertz乘积法对切趾函数的匹配性要求高,干涉图非对称切趾旁瓣抑制效果差、光谱分辨率低的缺点,综合Mertz法和Forman法的特点提出一种改进的相位校正方法。采用对称化方法将单边干涉图变换为双边干涉图、对称切趾、傅里叶变换重建功率谱,并采用对称化的双边干涉图傅里叶变换求取高分辨率的相位谱,提高相位校正的精度。通过仿真分析了非对称窗函数较对称窗函数有比较宽的主瓣宽度、高的旁瓣幅值,分辨率降低;实验验证该改进的相位校正方法功率谱误差小、计算量少,且光谱分辨率比较高,达到2cm-1。 相似文献
7.
针对远场声全息成像分辨率较差的问题,提出多孔声全息方法。利用多个小型传声器阵列进行优化布置,可以有效地提高分辨率,达到等效大阵列的声场可视化效果。首先推导了空间多孔加窗对远场Kirchhoff衍射积分声全息带来的干涉叠加效应;然后对主瓣宽度和旁瓣高度进行了定量计算,阐述了多孔优化布置方法,实现了旁瓣抑制条件下的分辨率最优;最后利用双音箱实验,验证了多孔声全息的可行性和理论分辨率,证明了多孔声全息方法的有效性。研究表明,多孔声全息的干涉叠加方法可以有效提高远场测量的重建分辨率,多孔声全息的优化设计方法可以实现旁瓣抑制条件下的分辨率最优。 相似文献
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基于计算机仿真技术,以光学干涉实验和滤波实验为研究对象,应用Matlab软件数值模拟了杨氏双缝干涉实验和多光束干涉实验干涉图形和光强分布图,数值模拟了光学滤波实验字母滤波后的频谱图和字母成像图,结果表明,计算机仿真结果能够清晰的表达出实验和理论的效果。研究结果为光学实验的课堂教学提供了参考。 相似文献
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快速傅里叶变换(FFT)是主要的激光多普勒测速系统信号处理方法,由于受到频谱泄露和栅栏效应的影响,其处理精度并不理想。基于Nuttall窗三谱线插值法的激光多普勒信号处理方法就是一种好的处理方法,它可以有效地抑制频谱泄漏和栅栏效应,改善信号分析精度,提高速度测量精度。由于Nuttall四项余弦窗的能量集中在主瓣,旁瓣非常小,因此加Nuttall四项余弦窗的FFT三谱线插值算法能够极大地减小频谱泄漏的影响,谱间干扰也很小,能很好地减小频谱泄漏和栅栏效应。 相似文献
12.
《中国光学快报(英文版)》2015,(6)
In order to select a suitable spatial filter for the spatial filtering velocimeter, the filtering characteristics of the spatial filters with a rectangular window and rectangular transmittance are investigated by the power spectrum of transmittance function method. The filtering characteristics of differential filters are investigated and compared with that of common ones. The influences of the number of spatial periods on the spectral bandwidth,deviation to central frequency, and peak transmittance are deeply analyzed. The results show that the influence is due to the form of superposition of the signal components and other components, the pedestal and higher-order components, and the superposition results from the finite size of the spatial filter. According to the results, a method is proposed to compensate for the deviation to central frequency. 相似文献
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根据相似性准则,对采集到的干涉图像进行干涉图元的拆分,通过寻址定位,得到与离散光程差序列相匹配的采样干涉图序列。采用过零采样方式,对大单边干涉图序列与小双边干涉图序列利用不同的窗函数进行切趾。为了校正相位误差,结合所研究采样干涉图的特点,对频域光谱乘积校正和空域干涉图卷积校正进行了研究和改进,获得了比较理想的光谱线形,其中空域干涉图卷积校正后的光谱偏差仅为0.012088,具有最好的校正效果。 相似文献
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基于线阵CCD空间滤波效应的航空相机像移速度测量方法 总被引:4,自引:2,他引:2
基于空间滤波测速原理,提出了利用线阵CCD空间滤波效应进行航空相机像移速度测量的新方法。对线阵CCD输出图像进行隔行采样,模拟了多狭缝的空间滤波特性,实现了对航空相机像移速度的光学非接触测量。通过研究空间滤波器的功率谱密度函数,对影响线阵CCD空间滤波特性的关键因素进行了特性分析,并在实验上验证了利用线阵CCD推扫图像模拟多狭缝空间滤波器测量像移速度的可行性。结果表明,对于5~53.2 mm/s范围内的像移速度,测量误差导致的像移量误差不大于1/3 pixel,能够满足航空相机像移补偿精度的要求。 相似文献
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运用张量分析方法把轴对称系统中的空间频率域的柯林斯公式推广到一般的非轴对称光学系统,并推导了在空间频率域中适用于非轴对称光学系统的张量ABCD定律。空间频率域中的柯林斯公式和张量ABCD定律直接给出了像散光束的空间傅里叶频谱的传输规律。它们在处理与空间频谱有关的问题,如空间滤波,成像系统的传递函数,复杂像散高斯光束在自由空间的传输等问题时更为简便。 相似文献
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Temporal modulation transfer functions based upon modulation thresholds. 总被引:11,自引:0,他引:11
N F Viemeister 《The Journal of the Acoustical Society of America》1979,66(5):1364-1380
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Barwick S 《Optics letters》2011,36(15):2827-2829
The primary interest in the finite-energy Airy beam derives from the special properties possessed by the maximum intensity at its central lobe. However, the defining spatial dependence, the Airy function, is an oscillatory function that consists of decaying side lobes. For some applications these side lobes may create deleterious effects. Fortunately, a nonsymmetric apodization of the beam in Fourier space is shown to enhance the central lobe as the side lobes are reduced and clipped. The properties of the central lobe are unaffected over a large proportion of the propagation path. 相似文献
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In this paper, a new digital method has been developed for eliminating the zero-order and conjugate image in off-axis digital holography. The method consists of filtering the spatial frequencies associated with these undesired terms (the zero-order and conjugate images) in the computed Fourier transform plane of the hologram multiplied with computer simulated original reference wave (written as (RIh)). An important conclusion is that, without the need for additional shift-spectrum process, the spectrum of real image always appears in the center of the spectrum plane and never shifts. This brings us some convenient to design a filtering window. The theoretical analysis and the corresponding simulation and experiment results are given. As the zero-order and conjugate image are eliminated, both the contrast and brightness of the real image are enhanced and the image quality is improved. Meanwhile, the process of designing a filtering window is simple and convenient. 相似文献
19.
E. C. Njau 《Il Nuovo Cimento C》1989,12(4):487-494
Summary We show that the frequencies of atmospheric molecular thermal vibrations significantly influence the spectral positioning
of the terrestrial window. The bandpass filtering process of this window is confined to the region starting from theE-region and extending to an altitude not exceeding about 600 km. This indicates that a significant part of the infrared radiation
emanating from lower altitudes is absorbed directly into the ionosphere. Implicitly, the infrared radiation field as viewed
downward from the top of the ozonosphere is continuously ?mapped? into the ionosphere in terms of temperature and hence ionization
variations. This mapping may be a vital cause of ionospheric irregularities. Factors that influence the transmission coefficient
of the terrestrial window are mentioned and discussed. In particular, it is shown that if the terrestrial thermal radiation
shifts in response to a temperature change in accordance with Wien's displacement law, the terrestrial window cannot correspondingly
shift and continue aligning itself approximately with the peak of the spectrum unless different atmospheric molecules dominate
the vibrational process. However, whether different molecules dominate the vibrational process or not, a change in atmospheric
temperature makes the transmission coefficient of the window change in the same sense. Consequently, the much reported role
played by the window in moderating the temperature of the Earth-Atmosphere system is apparently carried out even when the
latter temperature changes provided that the accompanying adjustments do not put the spectral location of the window completely
off the terrestrial radiation spectrum. Finally it is shown that if certain substances are introduced in sufficient quantities
into the troposphere (in gaseous or aerosol forms), the bandpass filtering process of the terrestrial window may consequently
operate in the latter and hence cause regional or global warming. 相似文献