水下目标前向声散射探测的干涉声场畸变量分析与应用

前向声散射探测中的信直比SDR;能衡量目标前向散射波与直达波的相对大小,但未考虑两种波的干涉叠加。前向散射波与直达波实际上是干涉在一起的且很难分离,因而信直比在目标探测分析中难以直接应用。以信直比为基础并计入前向散射波与直达波的干涉效果,引入了新的参量——干涉声场畸变量ΔFTL——并给出了理论计算公式。与SDR;相比,ΔFTL可以直接从声场数据中得到,在一定程度上具有不依赖先验信息的优势。以该公式为基础并结合千岛湖缩比目标探测试验数据,(1)通过估算几何扩展损失系数发现试验中的声波为球面波,结果与依据实测水文参数的射线声场模型仿真结果相符;(2)定量地证实了ΔFTL与目标穿越位置的对应关系,同时也证明了ΔFTL理论计算公式的有效性;(3)建立了一种新的直达波抑制效果评估方案,并完成了对自适应直达波抑制方法的效能评估。目标透声和航行姿态扰动对试验结果的影响可以忽略。分析结果表明:ΔFTL能够有效代替SDR,为开展前向声散射探测性能分析或直达波抑制效果评估提供理论参考。      

双基地有源探测柔性水平阵阵形实时校准方法

双基地有源模式下接收基地搭载的柔性水平阵在运动过程中,阵形会发生实时的畸变。针对阵形误差的存在会严重影响水听器阵列探测性能的问题,本文提出一种基于发射信号为线性调频(LFM)信号,利用直达波实现阵形参数估计的方法。该方法首先利用分数阶傅里叶变换(FRFT)对LFM信号在特定阶数的分数阶傅里叶变换域上的能量聚集性,实现直达波与目标回波的分离,避免了目标回波对于阵形参数估计的影响。而后利用各阵元直达波FRFT后对应峰值点之间的相位差实现了阵形参数估计,并提出了一种基于拖曳船辐射噪声的阵形解模糊方法。计算机仿真表明该方法对于噪声及干扰影响、入射角度误差以及多普勒频移均有一定的宽容性,湖上实验验证了阵形估计方法的有效性,是一种可实时校准、高精度、稳健的柔性水平阵阵形估计算法。     

浅海双基地有源探测调频信号直达波消除

双基地有源探测常采用长脉宽探测信号以获取更高的时间增益,容易导致回波弱信号被强直达波信号掩蔽而影响回波检测.针对长调频信号直达波的干扰,提出基于分数阶傅里叶变换(FrFT)的直达波消除方法.该方法利用调频信号在时频分布上的稀疏性,通过对接收信号进行分数阶傅里叶变换分离直达波和回波信号然后在变换域对直达波信号进行去除.远...     

利用多级时延估计与传递函数拟合的水下自干扰抑制法

提出了一种利用传递函数拟合与多级时延估计相结合的自干扰抑制方法来抑制接收信号中的强自干扰信号。首先通过频域解卷积估计发射泄漏的传递函数,进而构建出基本的对消信号,再通过互相关法与互谱法相结合的多级时延估计,精细补偿对消信号,获得良好的自干扰抑制效果。对实际海试数据的处理结果表明,当采用无人水下航行器(UUV)搭载一体化系统,在舷侧阵工作扇面内发射多帧线性调频(LFM)信号对目标船进行有源探测时,该方法的抑制比可达36 dB,且使得可检测回波的信干比从-30 dB降低到-55 dB,对后续的自干扰信号存在同样的抑制效果。以上结果表明该方法可抑制强自干扰信号,呈现出了较强的稳定性,使得淹没于强自干扰信号中的回波信号得以检测。     

基于动态阈值匹配追踪的主动声呐直达波抑制方法

双基地声呐中的直达波干扰可以通过重构抵消的方式进行抑制。这种方法需要对直达波信道进行估计，传统的正交匹配追踪算法的收敛速度慢，分步正交匹配追踪等算法在提高收敛速度时牺牲了信道估计精度，导致回波检测能力下降。本文提出一种动态阈值匹配追踪算法估计直达波的信道响应，在提高收敛速度的同时兼顾了信道估计精度。在仿真环境中，达到同样的直达波抑制效果，所提算法与传统正交匹配追踪算法相比，收敛速度显著提升，检测输出的回波强度比分步正交匹配追踪算法高4dB；海试数据处理结果中，所提方法迭代收敛速度较正交匹配追踪算法提升4倍；输出的回波强度比分步正交匹配追踪算法高2dB。     

稳健声线扰动特征用于浅海小目标定位*

针对海洋环境中的信道起伏变化对基于扰动声线声压敏感核的水下小目标定位算法影响较大的问题,提出了基于稳健声线扰动特征的目标定位方法,该方法首先对海洋环境中接收声场的到达结构进行分析,提取稳态的到达成分;然后通过观测稳健声线对应的接收信号在目标穿越过程中的扰动特征提取扰动声线;最后应用扰动声线类定位方法得到水下目标的定位模糊图实现定位。在浅海港口环境中开展了蛙人穿越实验,发射信号为中心频率为22.5kHz,带宽为15kHz的线性调频信号,实验数据的处理结果表明,直达路径和一次水底反射路径受信道起伏的影响较小,通过筛选稳健声线可以将扰动声线的定位方法用于自然的海洋环境。     

脉冲声信号影响锥特征的自适应选取EI北大核心CSCD

为了解决低信噪比下脉冲声信号影响锥特征的自适应选取和检测问题,提出了一种改进的整体嵌套边缘检测方法。利用脉冲信号小波域的时间-尺度分析谱图中明显的边缘效应特征,构造自适应影响锥(A-COI)模型。该模型可自适应输出最适影响锥部分,在减弱噪声干扰的同时最大程度的包含了脉冲信号的主要特征。进而将最适影响锥部分对应的小波系数用于脉冲信号检测,有效提升了低信噪比下的检测性能。对典型直升机桨-涡干扰脉冲信号的仿真和实验数据进行分析,结果表明在0 dB,2 dB,5 dB信噪比的复杂环境下,使用基于A-COI模型的检测率分别达到了65.13%,82.33%,95.27%,相对于传统固定大小影响锥的检测算法提升了42.42%,22.99%和2.36%。     

基于特征分析的自适应干扰抑制

针对水声环境中真实目标常常被强干扰掩盖而无法识别的问题,提出了一种基于特征分析的自适应干扰抑制方法(EAAIS)。根据目标信号可能的方向范围,通过构造合适的判决因子来自适应地估计并抑制互谱密度矩阵特征空间中的非目标信号子空间,得到具有更高信干比和信噪比的目标信号,为更好地实现目标识别与跟踪提供技术基础。数值仿真和海试数据验证结果表明,EAAIS方法能够自适应地抑制目标信号可能方向范围之外的强干扰,显著提高接收目标信号的信噪比和信干比,并获得更可靠的目标方位参数。相对于其它干扰抑制方法,本文提出的方法表现出了更为稳健的干扰抑制能力,具有更宽的适用条件。      

利用宽带声场频率-掠射角干涉结构的深海直达声区目标深度估计方法

针对典型深海环境中宽带声源的深度分辨问题,通过研究深海声场随频率起伏的干涉结构与垂直线阵频域波束输出图中的干涉结构,给出一种直达声区内可区分多水下目标的宽带声源深度估计方法。该方法以近水面目标的射线声场模型为基础,推导出近海面宽带声源接收声场的波束输出表达式,阐明了频域波束输出图中干涉结构与声源深度的对应关系。然后利用改进的傅里叶变换方法将二维频域波束输出图映射到声源深度-掠射角度域,可实现声源深度信息的有效分离。最后开展了深海实验验证,利用垂直阵接收拖曳声源发射的宽带白噪声信号,拖曳声源深度计算结果与实测声源深度基本一致。数值仿真与实验结果均表明该方法可以在多目标复杂环境下准确估计出水下宽带声源的深度。      

基于扩展信源熵值的穿墙成像雷达墙体强杂波抑制

提出了基于扩展信源熵值理论的超宽带穿墙成像雷达墙体强杂波抑制方法. 首先将回波信号离散化, 计算离散信源的概率空间并对该离散信源进行扩展, 计算得到扩展后含有墙体强杂波和目标回波的新信源的熵值. 然后根据墙体杂波熵值与目标信号熵值的差异设定门限, 自适应选取最佳门限调节因子, 对回波信号进行杂波抑制处理. 经过墙体强杂波抑制处理后, 利用后向投影方法对目标进行成像. 以基于时域有限差分方法(Finite Difference-Time Domain, FDTD) 的仿真软件GprMax2D/3D所获得的穿墙雷达数据进行仿真实验, 分别通过基于信源熵值的方法与本文所提方法来抑制墙体强杂波并成像, 通过对比结果可知, 前者的目标-杂波比增量为15.51 dB, 后者的目标-杂波比增量为19.74 dB. 因此, 本文所提方法能够在相同测量方式下得到更为精确的成像, 而且可以在保证成像效果的前提下大大减少天线扫描次数.     

自适应直达波抑制方法在前向散射宽带信号中的应用（英文）

The basic principles of target detection by forward acoustic scattering are presented.A direct blast suppression approach based on adaptive filtering(DBS-AF) is proposed to suppress the direct blast.The DBS-AF technique is extended to the linear frequency modulation(LFM) signal,where the envelope of the signal is regarded as a "general waveform" and imported into the adaptive filter.Application of the DBS-AF method to the data collected from a lake trial yields an output detection curve,in which the direct blast is mapped to the background while the acoustic field aberration is represented by the peak value fluctuation.The inhibitory effect in single hydrophone is approximately- 5 dB,and is then enhanced by exploiting the mean value removal approach as a preprocessing technique.The direct blast is further suppressed to a level of-10 dB by making full use of multichannel receptions.The main factors affecting the algorithm performance are as follows:the fluctuation degree of the receptions during the weighting vector training period and the power ratio of the forward scattered wave to the direct blast when the target is present.     

基于光频调节的干涉型光纤水听器相位补偿检测方法

提出了一种基于光源频率调节的干涉型光纤水听器主动相位补偿的信号检测方法。详细介绍了该方法的基本检测原理,对信号解调误差进行了理论分析与仿真。为了验证该方法的可行性,搭建了实验系统,并编写了实时的信号采集、处理程序,对某一干涉型光纤水听器的声压灵敏度进行了测试。在频带20 Hz-1.3 kHz上,平均声压灵敏度为-162.2 dB(0 dB=1 rad/μPa),波动小于±0.8 dB,与采用相位载波调制解调方法测量的结果基本吻合。实验结果证明该方法是有效的。由于传感部分不含有源器件,便于实现全光纤化,且解调算法简单、检测频带宽,该方法能被广泛应用到各种干涉型光纤传感器的信号检测当中。     

浅海小目标前向散射的非互易时反检测方法

将无源非互易时反(NRTR)用于浅海小目标前向散射探测海上实验研究,提出了一种基于频域加权松弛的信道估计算法(WRELAX)和时反方法相结合的小目标探测算法(WRELAX-NRTR)。该算法采用高精度的信道响应估计实现信道的空-时匹配,利用目标引起的时反声场结构的畸变检测前向散射信号对声场的扰动实现目标探测,并通过阈值法实现目标判决。在15~30 kHz的信号频率范围内进行海上实验,数据的处理结果表明,提出的WRELAX-NRTR探测算法与传统的NRTR算法相比,环境背景的扰动幅度从10 dB减小到4 dB,从而降低了虚警率,另外该算法对海洋环境噪声、目标聚焦深度、目标穿越距离和信道动态变化等均具有良好的鲁棒性。      

干涉型光纤水听器伪工作点控制检测方法

提出了一种用于干涉型光纤水听器信号检测的伪工作点控制方法.为了验证该方法的可行性,搭建了干涉型光纤水听器声压灵敏度测量系统,编写了实时信号采集和处理程序,对某一光纤水听器进行了测量.在频带20 Hz~2.5 kHz上,该光纤水听器的声压灵敏度为－156.5 dB(0 dB=1 rad/μPa),频响波动<±0.8 dB,与采用PGC调制解调方法测量的结果基本一致.由于传感部分不含有源器件,该方法实现了无源检测.另外,它还具有解调算法简单、检测频带宽等优点.     

Performance of an adaptive beamforming noise reduction scheme for hearing aid applications. II. Experimental verification of the predictions

A method to predict the amount of noise reduction which can be achieved using a two-microphone adaptive beamforming noise reduction system for hearing aids [J. Acoust. Soc. Am. 109, 1123 (2001)] is verified experimentally. 34 experiments are performed in real environments and 58 in simulated environments and the results are compared to the predictions. In all experiments, one noise source and one target signal source are present. Starting from a setting in a moderately reverberant room (reverberation time 0.42 s, volume 34 m3, distance between listener and either sound source 1 m, length of the adaptive filter 25 ms), eight different parameters of the acoustical environment and three different design parameters of the adaptive beamformer were systematically varied. For those experiments, in which the direct-to-reverberant ratios of the noise signal is +3 dB or less, the difference between the predicted and the measured improvement in signal-to-noise ratio (SNR) is -0.21+/-0.59 dB for real environments and -0.25+/-0.51 dB for simulated environments (average +/- standard deviation). At higher direct-to-reverberant ratios, SNR improvement is systematically underestimated by up to 5.34 dB. The parameters with the greatest influence on the performance of the adaptive beamformer have been found to be the direct-to-reverberant ratio of the noise source, the reverberation time of the acoustic environment, and the length of the adaptive filter.     

Physical model of acoustic forward scattering by cylindrical shell and its experimental validation

Research on the underwater target scattering can provide important theoretical support for target detection. The scattering model of cylindrical shell is established in this paper. It is found that the forward target strength is much stronger and varies with angles of incident wave less significantly than backward target strength. The received forward signal strength fluctuates with the target moving due to the interference between direct signal and scattering signal, which is most significant when target approaches the baseline. An experiment is carried out in an anechoic tank to validate the scattering model. The method of acquisiting forward scattering in the tank is proposed. The forward and the backward target strengths are achieved by using the pulse compression technology, and they are about 3dB less than the modeling results. The forward scattering phenomena of quiescent and moving target are measured, which are similar to modeling results with different target types.     

分布反馈式光纤激光水听器拖曳线列阵实验研究

为了进一步增大光纤拖曳阵的探测距离,研制了缆径为16mm的32元分布反馈式光纤激光水听器拖曳线列阵.阵元在10~2 000Hz频率范围内的平均声压灵敏度为-142.7dB(re 1rad/μPa),波动幅度小于±2dB.基于声光调制器的时分、波分联合复用技术实现了32元光纤激光水听器的多路复用,各个阵元之间以及各个通道之间的串扰均小于-40dB,并完成了静态和动态拖曳湖上实验.实验结果表明,研制的32元分布反馈式光纤激光水听器拖曳线列阵无论是在静态,还是在6~16节的动态拖曳状态,都能对目标形成稳定的波束指向,与GPS轨迹记录完全一致,展现了分布反馈式光纤激光水听器拖曳线列阵在工程上的应用前景.     

What do evoked potentials tell us about the acoustic system of the harbor porpoise?

The evoked acoustic potentials of the brainstem (EAPB) were detected from the brain, the skull, and the surface of the head of the harbor porpoise (Phocaena phocaena). Experiments were performed at the Karadag biological station (Crimea). Clicks, noise, and tone bursts of different frequencies within 80–190 kHz were used as stimuli. The time and frequency selectivities of the auditory system were estimated by the simultaneous and direct forward masking methods. The minima of EAPB thresholds were usually observed in a frequency range of 120–140 kHz, which corresponded to the main spectral maximum of the species-specific echolocation signal. In addition to the regular EAPB, a pronounced off-EAPB was observed. In the aforementioned frequency range, a frequency selectivity (Q₁₀ of about 10) was revealed by the direct forward masking method. The EAPB could be measured up to a frequency of 190 kHz, but outside this high-resolution region (outside the ultrasonic “fovea”), the frequency selectivity was weak. A simultaneous masking of a click by a tone was strong only when the delay of the click with respect to the masker onset was smaller than 1.0 ms. In a continuous regime, the tone (unlike noise) produced only a weak masking. The response to a small intensity increment of 1–4 dB was rather strong. In the frequency range of 120–140 kHz, this response exhibited a nonmonotone dependence on the signal level. The time resolving power, which was measured by the EAPB recovery functions for double clicks of various levels, was rather high, even when the intensity of the test signal was 18 dB lower than the masker level. Experimental data show that the auditory system of the harbor porpoise is tuned to detecting ultrasonic echo signals in the frequency range within 120–140 kHz. A hypothesis is put forward that the acoustic system of the harbor porpoise allows the animal, from analyzing echo signals, to estimate not only the distance to the target and the target’s intrinsic properties but also the speed with which the target is approached, the latter estimate being presumably obtained on the basis of the Doppler effect.     

连续波主动声呐的直达波抑制处理方法研究*

针对连续波主动声呐面临的强直达波干扰掩蔽目标回波的问题,该文在双基地配置已知的前提下,提出基于声屏蔽和常规方向零陷的联合抑制方法。即在精确的发射点声屏蔽的基础上,利用常规方向零陷技术减少声源附近方位的能量影响,从而达到更好地消除强直达波干扰的目的。仿真结果表明,在极低的信干比条件下,联合抑制方法比声屏蔽方法、常规方向零陷方法具有更好的干扰抑制性能。该方法可以有效减少连续波主动声呐的直达波的影响,在时间-距离模糊度图上得到清晰的目标位置。