利用多角度海底反向散射信号进行地声参数估计

针对现有海底地声参数估计方法的不足,提出了利用相控参量阵浅地层剖面仪接收的多角度海底反向散射信号进行地声参数估计的方法,首先利用正下方和斜入射方向上沉积层上、下表面的差频反向散射信号进行沉积层厚度和声速估计,然后利用正下方沉积层上、下表面两个不同频率的差频信号的反向散射信号估计沉积层衰减系数,最后利用正下方沉积层上表面原频反向散射信号估计沉积层阻抗,计算沉积层密度从而解决和声速的耦合性,通过水池试验验证了该方法的有效性。     

基于子带分解的宽带波束域最小方差无畸变响应高分辨方位估计方法研究

针对最小方差无畸变响应法对宽带不适用、计算量较大和如何与实际声呐系统结合这三个问题,提出了基于子带分解的宽带波束域MVDR高分辨方位估计方法:它以子带分解的方法实现MVDR在宽带情形下的扩展;利用波束转换实现降维运算,大大减小运算量和提高算法的稳健性;并且提出了在声呐系统使用中的新思路:可将该方法与声呐的多波束系统结合,直接利用声呐多波束系统的输出,可省去从阵元域到波束域的转换,进一步减少运算量;可用于替代传统的分裂波束精测定向系统或单波束系统,提高整个声呐定向系统的性能。经过理论分析、仿真实验和湖试实验,证明了该方法是简单的、有效的、可行的。     

基于动态载波AM算法参量阵的DSP设计与实现

为了解决普通AM参量阵产生的解调信号质量差、效率低等问题,设计了一个动态载波AM算法。以此算法为基础设计了一个DSP处理平台,并在此平台上实现了参量阵系统。经过系统硬件和软件两方面的优化设计,保证了算法运行的实时性和稳定性。最后,使用500Hz、800Hz和1100Hz的合成波作为测试信号,测试了系统输出的波形和参量阵前方5米处的频谱。对比测得的波形和理论波形,验证了此系统能够可靠地运行。对比普通AM和动态载波AM参量阵输出信号的频谱图,验证了动态载波AM参量阵能输出更好信噪比和能量更高的解调信号。     

阵不变量匹配主动声呐目标深度辨识

水面/水下目标深度辨识可以在主动声呐探测过程中快速筛选感兴趣目标。根据目标多径返回信号到达时间与目标深度的关联性,该文提出了基于水平线阵的主动脉冲响应匹配目标深度辨识方法,该方法利用主动信号传播特性结合阵不变量理论提取脉冲响应,并与拷贝声场匹配实现目标深度估计。在校正了目标多径回波的方位变化后,该方法提取的时域特征较为稳定,并且只在时延估计距离处进行深度搜索。通过水平阵收集的宽带实验数据,在连续的多次回波中实现了对水面/水下目标92%的辨识成功率,验证了该方法在浅海环境下的目标深度估计能力。     

一种基于单水听器的浅海水下声源被动测距方法

针对浅海波导中宽带脉冲声源的被动测距问题,本文在群延迟理论的基础上,与warping变换处理相结合,提出了一种适用于浅海波导中宽带声源的单水听器被动测距方法.利用warping变换可以实现对脉冲声源接收信号各阶简正波的分离提取,对分离后的简正波进行时频分析处理可以得到各阶简正波到达时刻和频率之间的关系,即各阶简正波的频散曲线,从而得到任意两阶简正波到达接收水听器的时延差.海底相移参数P是描述海底地声参数的一个重要参量,包含了海底地声参数信息,在海底环境参数未知而P已知的情况下,利用P和简正波水平波数之间的关系可以求得任意两阶简正波的?S_(g,mn)(群慢差).根据群延迟理论,利用得到的任意两阶简正波的时延和?S_(g,mn)可实现利用单水听器对水下声源进行被动测距.本文提出的测距方法测量简单、计算方便,具有较强的实用意义.数值仿真和海上实验数据处理结果的测距误差都在10%以内,证明了该方法的有效性.     

一种基于简正波模态频散的远距离宽带海底参数反演方法

在浅海环境中, 海底环境参数对声传播有着重要的影响. 由于利用单个宽带声源进行海底参数反演时, 随着距离的增大, 误差变大, 本文提出利用warping变换对在浅海波导中传播的, 不同距离上的两个宽带爆炸声源进行简正波的有效分离, 实现了宽带爆炸声源的远距离海底参数反演. 采用全局寻优遗传算法对提取出的模态频散到达时间差与理论计算的模态频散到达时间差进行匹配处理, 并结合随距离连续变化的声传播损失, 实现了利用单水听器进行海底参数的反演. 实验结果表明: 运用反演出的海底参数提取模态频散时间差和实测数据提取出的模态频散时间差吻合得较好; 而通过传播损失反演得到的海底衰减系数与频率呈指数关系. 最后, 对反演结果进行了后验概率分析, 并将本组爆炸声源的反演结果用于另一组不同距离上爆炸声源时仍然有效, 来评价反演结果的有效性.     

一种相位调制激光多普勒频移测量方法

对相位调制拍频信号随信号光频率变化规律进行分析,发现拍频信号相位参量的频谱包含两个在值域上彼此分开的单调边缘,表明利用拍频信号的相位参量可以进行多普勒频移测量.如果利用拍频信号振幅参量对出射激光进行工作点锁定,其多普勒频移测量范围是Fabry-Perot干涉仪边缘技术的两倍.理论分析拍频信号振幅和相位参量的提取方法,表明基于此拍频信号相位参量的测量方法无需进行信号光能量检测,与Fabry-Perot边缘技术方法相比,结构更简单,且少了一条外部噪音混入的通道.为了对该多普勒频移测量方法定量分析和参量优化,利用误差合成原理以及计算机仿真,推导出其测量误差公式.根据测量原理搭建了实验系统,用频率可调光纤激光器的输出光模拟多普勒频移信号光进行测量,结果表明鉴频参量及其误差分布曲线的测量结果与理论分析相符合.     

光学系统像差与光场干涉对激光参量测量精度的影响

研究了采用面阵CCD探测器测量光束参量的技术问题,研制了一套高精度激光参量测量系统,对其光学系统像差与光场干涉原因进行了理论分析,实验测量了连续抽运1064nm固体模式发生器产生的基模厄米高斯光束,分析对比了其输出光束带有干涉条纹时对测量精度的影响,对光学系统的设计提出了具体技术要求,为同类装置的研制提供了参考依据。     

一种检测低信噪比下未知波形时变相干信号的方法*

从获取的数据中检测目标信号,是雷达、声呐等领域重要的研究内容。时频域严重畸变的回波信号以及时变线谱信号的自适应检测,具有重要意义。为了挖掘和推广自适应相干累积（Adaptive Coherent Integration,ACI）技术在未知时变信号检测领域的能力,本文给出了ACI算法的基本原理,并进行了系统性地理论推导,得到了ACI算法的宽带时变自回归滑动平均模型（ARMA）和窄带复解析模型。利用这些模型解释了产生信号相干累积的机理,分析得出了产生相干累积的条件,揭示了这种时变系统的许多奇异特性。结合仿真实验和实际海上实验数据对ACI算法展开验证,结果表明ACI算法对于低信噪比下未知波形信号具有优异的检测能力,展示出ACI算法在水下探测等相关领域存在广泛的实际应用前景。     

压缩感知在宽带声学多普勒测速技术中的应用*

为降低宽带声学多普勒测速技术中宽带回波信号处理系统的采样和数据存储压力,研究了压缩感知的回波信号重构算法,并将其应用于宽带声学多普勒测速的回波信号分析中。在点回波模型下进行宽带回波信号的仿真实验,利用复协方差法计算频移。仿真实验结果表明,在无噪声的理想条件下,利用压缩感知理论处理宽带多普勒测速的回波信号,能够达到理想的测频效果;在相同的噪声条件下,应用压缩感知方法处理后的回波信号能够获得与带通采样方法相当的测频效果。     

Dispersion of the signal of a parametric array in shallow water

Results of an experimental study of shallow-water propagation are presented for a broadband acoustic signal produced by a parametric array. The narrow-beam character of the signal provides single-mode excitation of the oceanic waveguide. The possibility of compression of the broadband signal in the course of its propagation in shallow water is discussed for the case of a specially adjusted frequency modulation. The use of waveguide dispersion leads to an increase in the efficiency of parametric radiation in shallow water.     

A parametric antenna for hydrophysical research on long-distance paths

This work considers the capabilities of a hydroacoustic antenna based on principles of nonlinear acoustics to perform hydrophysical studies on long-distance paths. The antenna is described and results from initial experiments at sea are reported. The antenna is installed at a depth of 40 m at the site of investigations by the Hydrophysical Institute, Abkhazia Academy of Sciences. At a pumping frequency of 20 kHz, it allows the medium to be probed in the 300–3000 Hz range of parametric radiation on long-distance routes. The sharp directional pattern (2° angular resolution) of the broadband parametric radiation ensures single-mode excitation of the marine waveguide throughout the frequency band. Generation of a specific signal by a parametric antenna provides conditions for using the frequency dispersion of the velocity of acoustic signal propagation in the marine waveguide to compress the signal as it travels along a long-distance path.     

利用等离子体声源测量浅海低频段水声信道特性

浅海水声信道的结构特征及其变化特性是浅海环境水下远程探测和通讯应用的基础.为了有效测量低频水声信道特性,我们在实验中采用了拖曳等离子体声源和垂直阵接收系统。通过实验测量与信道模型仿真输出的比较,对等离子体声源特性,特别是脉冲波形、空间指向性和电声转换效率,以及在信道中的传播特性等进行测量分析。结果表明:实验测量与信道模型仿真符合良好,实验中采用的等离子体声源的发射源级和拖曳姿态稳定,波形一致性好,可以满足走航式连续水下信道测量要求。      

Temporal coherence of sound transmissions in deep water revisited

This paper examines the signal coherence loss due to internal waves in deep water in terms of the signal coherence time and compare to data reported in the literature over the past 35 years. The coherence time of the early raylike arrivals was previously modeled by Munk and Zachariasen ["Sound propagation through a fluctuating stratified ocean: Theory and observation," J. Acoust. Soc. Am. 59, 818-838 (1976)] using the supereikonal approximation and by Dashen et al. ["Path-integral treatment of acoustic mutual coherence functions for arrays in a sound channel," J. Acoust. Soc. Am. 77, 1716-1722 (1985)] using the path integral approach; a -1 [corrected] power frequency dependence and a -1/2 [corrected] power range dependence were predicted. Recent data in shallow water in downward refractive environments with internal waves suggested that the signal coherence time of the mode arrivals follows a -3/2 power frequency dependence and a -1/2 power range dependence. Since the temporal coherence of the acoustic signal is related to the temporal coherence of the internal waves, based on the observation that the (linear) internal waves in deep and shallow waters have a similar frequency spectrum, it is argued that the modelike arrivals in deep water should exhibit a similar frequency dependence in deep and shallow waters. This argument is supported by a brute-force application of the path integral to mode arrivals based on the WKB relation between the ray and mode. It is found that the data are consistent with the -3/2 power frequency dependence but more data are needed to further test the hypothesis.     

Shallow water sound propagation with surface waves

The theory of wavefront modeling in underwater acoustics is extended to allow rapid range dependence of the boundaries such as occurs in shallow water with surface waves. The theory allows for multiple reflections at surface and bottom as well as focusing and defocusing due to reflection from surface waves. The phase and amplitude of the field are calculated directly and used to model pulse propagation in the time domain. Pulse waveforms are obtained directly for all wavefront arrivals including both insonified and shadow regions near caustics. Calculated waveforms agree well with a reference solution and data obtained in a near-shore shallow water experiment with surface waves over a sloping bottom.     

Frequency invariability of acoustic field and passive source range estimation in shallow water

The frequency invariability of the warped modal signal and the warped signal autocorrelation function in shallow water is discussed.A method is proposed for passive source-range estimation based on the frequency invariability and warping transform of signal autocorrelation function received by a single hydrophone in a range-independent or weak range-dependent shallow water environment.In the method,a guided source with a known range is employed to provide the crucial and relative invariant scaled features.The experimental data in shallow water with an iso-speed profile and a fluctuated thermocline are used to verify this approach.The relative errors of the source range estimation are basically less than 10%.     

Acoustic analysis by spherical microphone array processing of room impulse responses

Spherical microphone arrays have been recently used for room acoustics analysis, to detect the direction-of-arrival of early room reflections, and compute directional room impulse responses and other spatial room acoustics parameters. Previous works presented methods for room acoustics analysis using spherical arrays that are based on beamforming, e.g., delay-and-sum, regular beamforming, and Dolph-Chebyshev beamforming. Although beamforming methods provide useful directional selectivity, optimal array processing methods can provide enhanced performance. However, these algorithms require an array cross-spectrum matrix with a full rank, while array data based on room impulse responses may not satisfy this condition due to the single frame data. This paper presents a smoothing technique for the cross-spectrum matrix in the frequency domain, designed for spherical microphone arrays, that can solve the problem of low rank when using room impulse response data, therefore facilitating the use of optimal array processing methods. Frequency smoothing is shown to be performed effectively using spherical arrays, due to the decoupling of frequency and angular components in the spherical harmonics domain. Experimental study with data measured in a real auditorium illustrates the performance of optimal array processing methods such as MUSIC and MVDR compared to beamforming.     

空气中快速运动声源水下声场的波数积分模型

本文采用二维波数积分，对空气中高速运动声源激发的水下声场进行建模。针对二维波数积分计算声场时域解计算量大的问题，提出一种快速计算方法。用本文提出的方法，对深海和浅海情况下，空气中高速运动单频点声源激发的水下声场进行了计算和仿真。计算结果表明：在深海，水下接收信号的幅度和瞬时频率随时间发生变化；接收器深度、接收器与声源运动轨迹的最小距离对接收信号的变化快慢有较大影响，而声源高度的影响较小；在浅海中，接收信号呈现快速的幅度起伏，明显的多普勒频移和大的频率展宽效应。与简正波方法相比，本文方法主要适用于近场计算，而简正波方法适用于远场。另外，当声源频率较高时，二维波数积分方法的计算量将迅速增大。     

微弱光学图像的光参量放大特性的研究

研究了微弱光学图像在光参量图像放大中的放大特性,分析了相位匹配和晶体的空间频率带宽对图像信号增益的影响,从实验上验证了不同的相位匹配时输入图像信号在傅里叶平面上的增益分布.结果表明,当晶体的空间频率带宽大于输入图像信号的空间频率带宽且完全相位匹配时,光参量图像放大器能够对输入图像信号实现无失真、高增益的理想放大;有相位失配时,图像信号的增益峰值向高空间频率范围移动,并且在峰值附近范围变窄,随相位失配量大小的变化能够对图像信号光场中某特定空间频率实现放大,对图像信号进行滤波处理,突出图像特定频率的信息,实现图像边缘增强.     

浅海负跃层条件下的双基地有源探测实验及定位声速修正

为了研究浅海条件下海底固定水平阵和机动声源的双基地有源探测性能,建立了浅海双基地有源探测仿真模型,分析了实验海区负跃层条件下的传播损失和多途能量扩展损失,实现了双基地有源探测的性能预估。以模型仿真为基础,在南海北部海域开展了一次浅海双基地有源探测实验.针对定位中的声速与实验中目标回波的脉冲传播速度的偏差导致定位精度下降的问题,提出了一种目标回波脉冲传播速度近似估计方法。实验结果表明,双基地有源探测可在浅海负跃层条件下实现对水中目标的有效探测,多个实验站位的回波信噪比实测值与仿真预测值符合较好,定位声速近似估计方法可进一步提高定位精度。