湍流大气中哈特曼传感器的模式波前复原误差II

 分别采用Zernike和Karhunen-Loeve两种模式波前复原法,分析了在子孔径斜率测量噪声影响下,哈特曼传感器对大气湍流畸变波前的模式复原误差与模式复原阶数等的关系。发现最优模式复原阶数主要与哈特曼传感器的子孔径斜率探测信噪比有关。分析了一个哈特曼传感器对实际大气湍流畸变波前的测量结果,给出了确定传感器测量噪声的方法。     

Virtual sensors for active noise control in acoustic-structural coupled enclosures using structural sensing: part II--Optimization of structural sensor placement

The work proposed an optimization approach for structural sensor placement to improve the performance of vibro-acoustic virtual sensor for active noise control applications. The vibro-acoustic virtual sensor was designed to estimate the interior sound pressure of an acoustic-structural coupled enclosure using structural sensors. A spectral-spatial performance metric was proposed, which was used to quantify the averaged structural sensor output energy of a vibro-acoustic system excited by a spatially varying point source. It was shown that (i) the overall virtual sensing error energy was contributed additively by the modal virtual sensing error and the measurement noise energy; (ii) each of the modal virtual sensing error system was contributed by both the modal observability levels for the structural sensing and the target acoustic virtual sensing; and further (iii) the strength of each modal observability level was influenced by the modal coupling and resonance frequencies of the associated uncoupled structural/cavity modes. An optimal design of structural sensor placement was proposed to achieve sufficiently high modal observability levels for certain important panel- and cavity-controlled modes. Numerical analysis on a panel-cavity system demonstrated the importance of structural sensor placement on virtual sensing and active noise control performance, particularly for cavity-controlled modes.     

基于神经网络的航天光学遥感器在轨信噪比测试方法

提出一种基于神经网络的航天光学遥感器在轨信噪比的的测试方法。通过模拟得到了大量的包含有不同信噪比等级的遥感图像,并将其作为网络训练和测试的样本。通过对遥感图像进行分析,找到了分别与景物结构和噪声有关的特征向量,并将其作为神经网络的输入。在对大量样本图片进行训练后,可完成对由遥感器传输下来的任意一幅地面景物图像进行信噪比的测试,从而避免了传统方法对特定地面景物目标在成像测量中的诸多弊端,平均测量误差约为10%。     

基于反射型延迟线结构的无线无源声表面波测温系统

从传感器核心元件及无线测温雷达的优化设计出发,研制了一种集成电子标签的高性能声表面波(SAW)无线无源测温系统。基于耦合模(COM)理论对作为传感元件的反射型SAW延迟线进行了优化设计,基于仿真结果,实验研制了采用YZ LiNbO_3石英基片的434 MHz反射型SAW延迟线,该器件是由一个换能器与8个反射器构成的反射型延迟线,其中3个反射器用于温度检测,另外5个反射器则用于采用相位编码的电子标签。测试结果显示所研制的反射型SAW延迟线具有良好的时域特性与较高的信噪比,并与理论仿真结果极为吻合。设计并研制了采用步进调频(FSCW)模式的测温雷达,利用高精度高低温箱对所研制的无线无源SAW测温系统进行了无线测试,系统表现出良好的线性特性,测温准确度达到了士1℃以内。      

Children's recognition of American English consonants in noise

In contrast to the availability of consonant confusion studies with adults, to date, no investigators have compared children's consonant confusion patterns in noise to those of adults in a single study. To examine whether children's error patterns are similar to those of adults, three groups of children (24 each in 4-5, 6-7, and 8-9 yrs. old) and 24 adult native speakers of American English (AE) performed a recognition task for 15 AE consonants in /ɑ/-consonant-/ɑ/ nonsense syllables presented in a background of speech-shaped noise. Three signal-to-noise ratios (SNR: 0, +5, and +10 dB) were used. Although the performance improved as a function of age, the overall consonant recognition accuracy as a function of SNR improved at a similar rate for all groups. Detailed analyses using phonetic features (manner, place, and voicing) revealed that stop consonants were the most problematic for all groups. In addition, for the younger children, front consonants presented in the 0 dB SNR condition were more error prone than others. These results suggested that children's use of phonetic cues do not develop at the same rate for all phonetic features.     

Detecting subthreshold events in noisy data by symbolic dynamics

We show that a symmetric threshold crossing detector can be described by a symbolic dynamics of a static three-symbol encoding which is highly efficient to detect subthreshold events in noisy nonstationary data. After computing instantaneous word statistics and running cylinder entropies, we introduce a mean-field transformation of the three-symbol dynamics considered as a Potts-spin lattice onto a distribution of two symbols. This transformed word statistics enables one to derive an estimator of the signal-to-noise ratio (SNR). Subthreshold events are then proven by a prominent peak of the SNR estimator as a function of the noise intensity.     

Noise performance of multiplexed fiber-optic sensor systems with optical amplifiers

The signal to noise ratio (SNR) of a multiplexed fiber-optic sensor network can be improved by inserting fiber-optic amplifiers. Several configurations of amplifiers in the sensor network are analyzed. A single fiber-optic amplifier used as a preamplifier is a good solution with high SNR. However, by distributing amplifiers in the network even higher SNR can be obtained, and identical couplers can be used throughout the network.     

基于EMCCD的AOTF成像光谱仪噪声分析与信噪比研究

声光可调谐滤波器(AOTF)成像光谱仪是一种新型高光谱成像系统。针对系统存在的波段间辐射灵敏度差异较大,低照度条件下部分波段信噪较低的问题,引入了电子倍增CCD(EMCCD)作为感光器件。对该原理仪器在普通和电子倍增两种工作模式下的噪声进行了分析,推导了信噪比模型,并利用研制的原理样机进行了实验验证。在此基础上,提出了电子倍增模式下系统动态范围的评价方法,给出了以入瞳光谱辐亮度为判据的工作模式选择方法。结果表明,信噪比模型与实测结果吻合,电子倍增模式的合理选择有效提高了低照度条件下的信噪比,改善波段间辐射灵敏度的非一致性。     

Noise analysis of grating-based x-ray differential phase-contrast imaging with angular signal radiography

X-ray phase-contrast imaging is one of the novel techniques,and has potential to enhance image quality and provide the details of inner structures nondestructively.In this work,we investigate quantitatively signal-to-noise ratio(SNR) of grating-based x-ray phase contrast imaging(GBPCI) system by employing angular signal radiography(ASR).Moreover,photon statistics and mechanical error that is a major source of noise are investigated in detail.Results show the dependence of SNR on the system parameters and the effects on the extracted absorption,refraction and scattering images.Our conclusions can be used to optimize the system design for upcoming practical applications in the areas such as material science and biomedical imaging.     

Reduction of radiated exterior noise from the flexible vibrating plate of a rectangular enclosure using multi-channel active control

This study attempted to control the radiated exterior noise from a rectangular enclosure in which an internal plate vibrates by acoustic excitation and noise is thus radiated from that plate. Multi-channel active control was applied to reduce the vibration and external radiation of this enclosed plate. A piezoelectric ceramic was used as a distributed actuator for multiple mode control of the vibration and radiated noise in the acoustically excited plate. To maximize the effective control, an approach was proposed for attachment the piezoelectric actuator in the optimal location. The plate and internal acoustic space in the enclosure are coupled with each other. This will change dominant frequency characteristics of the plate and, thus, those of the externally radiated noise. Active noise control was accomplished using an accelerometer attached to the plate and a microphone placed adjacent to that plate as an error sensor under acoustic excitation of sine wave and white noise. It was found that the control of radiated external radiation noise requires a microphone as an error sensor, a sound pressure sensor due to vibration of the plate, differences in the dominant frequency of externally radiated noise, and complex vibration modes of the plate.     

Physical noise model of a uniformly doped nanoscale FinFET photodetector

The noise mechanisms of a uniformly doped nanoscale FinFET photodetector including quantum mechanical effects is investigated theoretically. A numerical model has been developed for computation of different noise components in nanoscale FinFET. The drain current channel thermal noise under illuminated conditions is calculated. The noise parameters of the nanoscale FinFET equivalent circuit are strongly influenced by the incident optical signal and the quantum mechanical effects are found to play a major role in determining the overall noise performance of the device. It also reveals that the operating frequency can be adjusted suitably to make the noise behavior independent of the incident optical power. Other noise components such as Shot noise, thermal noise and diffusion noise have been calculated for the two port FinFET photodetector. Signal-to-noise ratio (SNR), Bit error rate (BER) and noise equivalent power (NEP) has also been calculated.     

点源信标相关哈特曼-夏克波前传感器光斑偏移测量误差分析

在基于哈特曼-夏克波前传感器(SH-WFS)的自适应光学系统中,通常采用质心算法探测点源信标的子孔径光斑偏移量.然而质心算法探测精度受到诸如减阈值等因素的影响,在低信噪比(SNR )时不能准确估计光斑质心位置,而相关哈特曼算法不需要减阈值,具有更好的鲁棒性.本文在介绍相关SH-WFS基本原理的基础上,通过建立基于点源信标探测的相关SH-WFS算法的随机噪声模型,推导了光斑偏移测量误差表达式,系统分析了光子噪声、CCD读出噪声、背景光子噪声等因素对相关SH-WFS测量误差的影响.并进行了数值仿真及实验,仿真 关键词： 相关哈特曼-夏克波前传感器 相关哈特曼算法 质心算法 测量误差     

Effects of noise suppression on intelligibility: dependency on signal-to-noise ratios

The effects on speech intelligibility of three different noise reduction algorithms (spectral subtraction, minimal mean squared error spectral estimation, and subspace analysis) were evaluated in two types of noise (car and babble) over a 12 dB range of signal-to-noise ratios (SNRs). Results from these listening experiments showed that most algorithms deteriorated intelligibility scores. Modeling of the results with a logit-shaped psychometric function showed that the degradation in intelligibility scores was largely congruent with a constant shift in SNR, although some additional degradation was observed at two SNRs, suggesting a limited interaction between the effects of noise suppression and SNR.     

Accuracy of spectrum estimate in fluorescence spectral microscopy with spectral filters

We establish the accuracy of the spectrum that is estimated with an inexpensive fluorescence spectral microscope utilizing a small set of spectral filters [Soriano et al, Opt. Exp. 10, 1458–1464 (2002)]. The spectrum at an arbitrary image location of the fluorescent sample is estimated as a linear superposition of basis spectra that are derived by singular value decomposition (SVD) or principal component analysis (PCA) from a spectral library of fluorescence spectra. Estimation performance is analyzed as a function of library statistics, filter selection and sequencing, minimum negativity constraint and signal to noise ratio (SNR) of fluorescence image. We consider image SNR degradations that arise from weakening of image intensity, additive Gaussian noise, intensity-dependent Poisson noise and quantization errors. The recovery of specific spectral features like spectral resolution, general similarity and peak alignments, is assessed using Linfoot’s criteria of fidelity, structural content, and correlation. We found that estimation with SVD basis spectra is more robust against image noise than that with PCA basis spectra. However for high SNR images, accurate estimation is achieved more quickly with PCA basis spectra and with better response to the application of minimum negativity constraint.     

单载波频域均衡中的水声信道频域响应与噪声估计

本文对单载波频域均衡(SC-FDE)中的信道和噪声估计进行研究,理论分析了形成误码率平台的可能原因,提出了基于Chu序列的联合信道时频域响应和噪声功率估计算法.利用水声信道响应的稀疏特性和门限确定信道能量集中区域,进行信道估计的去噪处理和噪声功率计算.借助于水声射线模型对所提出的算法进行了仿真,分析了噪声估计对SC-FDE性能的重要影响.仿真结果表明,所提出的信道和噪声估计算法可以有效减缓或消除SC-FDE中的误码率平台.     

具有复合式法珀腔的光纤压力传感器的解调

对由三个反射面构成的复合式法珀腔的光纤法珀压力传感器进行了输出光谱理论分析,提取了含有传感器腔长信息的包络.提出了基于干涉级次拟合的解调算法,仿真分析了传感法珀腔腔长范围为160～215μm的光谱信号.结果显示,在不同信噪比下,基于干涉级次拟合的算法可获得较好的测量准确度,同一信噪比下,该准确度不依赖腔长变化,也不依赖光谱解调波长分辨率变化.实验结果表明,基于干涉级次拟合结果曲线残差的均方根差为0.012μm,验证了该算法的有效性.     

风成噪声背景下垂直阵阵列信噪比随声源深度的变化规律

风成噪声是海洋中最广泛存在的环境噪声、是被动声纳处理性能的重要影响因素.它具有一个典型的物理性质是很大程度上只对应中高阶模态.阵列信噪比计入了阵列采样辐射声强、背景噪声功率和阵处理增益,是决定声纳阵列处理性能的关键物理量.本文研究了受风成噪声模态结构影响,典型夏季浅海环境中垂直阵阵列信噪比随声源深度的变化关系.在简正波模深函数采样完整的假设条件下,理论证明了阵列信噪比随声源深度的变化可近似为低阶模态幅度强度(模深函数模值的平方)随深度变化的线性叠加,且模态阶数越低,贡献越大;并且,在强风成噪声背景、显著负梯度环境下该变化规律可由1阶模态幅度强度随深度的变化近似独立表征.以上结果表明,在同一声源距离条件下,声源置于水体下半部分时的阵列信噪比比置于海面附近更大,并且在位于1阶模态峰值点所在深度附近时达到最大.典型负声速梯度浅海环境中的仿真实验结果对理论分析进行了验证,并表明在一定条件下阵列信噪比随声源深度的变化与声源距离近似无关.     

Treatment of MZI sensor signal with an improved wavelet neighboring coefficients

In order to gain the wavelength drift of Mach–Zehnder interferometer (MZI) sensor system, achieve the measurement of ambient environment parameters precisely, so, need to treatment optical fiber sensing signal with noise. Firstly, introduce the method of neighborhood wavelet coefficient by analyzing the drawback of traditional wavelet de-noising methods. Secondly, an improved threshold is putted forward based on neighboring coefficients in this paper which is to overcome the shortcomings of traditional wavelet methods. Finally, the threshold function proposed by this paper deal with MZI sensing noisy signal together with improved threshold. The simulation result shows that the new method can get the better signal-to-noise ratios (SNR) and root of mean square error (MSE) simultaneously and gain the reconstruction signal of the higher correlation coefficient (CC). Compared with the soft and hard threshold method, its SNR increases by 2–4 db, and compared with NeighCoeff, its SNR improves by 1.2 db. The peak error is 1.6 pm. So, the system can meet the requirement of improving sensor detection precision.     

不同光谱型的低分辨率恒星光谱在不同信噪比条件下视向速度测量精度的分析

恒星的视向速度对于研究银河系的演化结构和动力学有很重要的意义,同时也是寻找变源和特殊天体的一种手段。不同的研究对其测量精度有不一样的要求。使用模板匹配的方法计算不同类型的低分辨率可见光波段恒星光谱的视向速度精度,从而为不同方面的科学研究提供有效可靠的参考。分别选取不同光谱型高信噪比的美国斯隆巡天恒星光谱,并加以噪声来模拟不同信噪比条件下的恒星光谱。通过分别计算这些恒星样本的视向速度,定量分析了各种类型的恒星在不同信噪比条件下能达到的视向速度测量精度。同时,还就白矮星的视向速度测量精度进行了分析。结果显示,对于相同信噪比的早型恒星的视向速度测量精度远没有晚型恒星的测量精度高,尤其是A型星的视向速度测量标准误差是K型星和M型星的5~8倍。分析其原因,主要是由于不同类型恒星的具有不同宽度的谱线所导致的。因此对于具有更宽谱线的白矮星光谱的视向速度测量误差更大,可达50 km·s-1。以上结论将为恒星科学研究提供很好的参考。     

Cross talk between holograms of finite contrast in a phase-code multiplexing system

The cross talk between holograms recorded in a phase-code multiplexing system is analyzed. The signal-to-noise ratio (SNR) is derived for the original image of a finite contrast ratio in the presence of a phase-shift error of the reference beam. It is shown that one particular code in the Walsh-Hadamard code set can be the dominant cross-talk noise source. We experimentally measured the SNR of the holograms recorded in an 8-bit phase-code multiplexing system by varying the contrast ratio of the original image. We show good agreement between experiment and theory. The existence of one bad code is also shown experimentally.