强混响背景下悬浮目标的时反成像

提出了一种加权宽带全信号子空间时反成像方法,将扩展性目标建模为有限数量个、相互独立的点散射体构成,实现了时反成像在可疑目标区域的全信号子空间和整个宽带的累加。在实验室波导水池中,底部放置圆柱筒制造混响背景,共进行了两个实验,一是扩展性的悬浮目标位于圆柱筒附近,其回波与圆柱筒反射的混响不在同一个时间窗内,二是弱点目标回波与圆柱筒反射的混响重叠于同一个时间窗内,对所提出的方法进行强混响背景下弱悬浮目标的成像能力验证。结果表明,此方法对强混响背景下的弱悬浮目标的成像质量明显优于传统的时反成像方法。      

利用起伏界面改善非消声水池中的声功率测量

针对非消声水池的声学测量应用,提出了一种在界面起伏的非消声水池中测量水下声源辐射声功率的方法。基于数值方法分析了在非消声水池中利用起伏界面改善低频声源辐射声功率测量的可行性,进一步在一个尺寸为1.2 m×1.0 m×0.8 m的非消声水池中开展实验研究,测量了水声换能器的辐射声功率。实验表明,相对于界面静止的水池,利用造波装置生成随机起伏界面后,声场扩散性明显改善:(1)水池的Schroeder频率从10015 Hz降低到8370 Hz,辐射声功率的测量范围向低频扩展;(2)结合空间平均技术测得的频响曲线起伏程度减小,与自由场值更接近,辐射声功率的测量结果更为准确。所提方法有助于提高非消声水池中水下目标声学特性的测量能力。     

Waveguide invariance structure for low frequency monostatic bottom reverberation mitigation in shallow water

The stable range-frequency interference structure(waveguide invariance) of the low frequency monostatic bottom reverberation in shallow water is derived theoretically in this paper by using ray-normal mode coherent reverberation model and separable bottom scattering model.And combined the concept of spectral subtraction,a reverberation forecasting and mitigating method based on the waveguide invariance is presented.According to the waveguide invariance,the reverberation intensity for a detecting range can be estimated from the reverberation returns scattered from some other range cells nearby the detecting range with frequency shift.Then the reverberation component for the detecting range in the echo can be canceled mostly by using the estimated reverberation intensity,so as to enhance the echo-to-reverberation ratio and improve the detection capability of the active sonar.Simulations in typical horizontal layered shallow water environment show the stability of waveguide invariance structure in the low frequency monostatic bottom reverberation and the efficiency of the reverberation forecasting and mitigating method based on the waveguide invariance.     

A method for detecting target echo in reverberation based on fractional Fourier transform

A method for detecting the target echo in reverberation was proposed based on fractional Fourier transform theory when the transmitted signal is linear frequency modulation signal. The slow time-varying envelope of reverberation is computed to process reverberation to be stationary. The stationary reverberation is cut into blocks using a sliding window. A narrow-band filter is applied in FrFT domain for each block and the signal is recovered through inverse FrFT. Output of the system is the energy of the recovered signal. When the target echo is included in one of the blocks, the reverberation noise is reduced, and the output is the energy of the target echo. All the simulation and lake experiment results show that the detection performance of the present method is better than that of the matched filter.     

水声信号稀疏重构高分辨角度-多普勒成像

针对傅氏空时二维谱估计分辨率低以及声呐空时采样数据样本数不足给角度-多普勒成像带来困难的问题,提出一种水声信号稀疏重构的高分辨角度-多普勒成像方法和抗混响空时滤波器的稀疏重构方法。该方法在声呐阵列单测量向量的极少观测样本条件下,建立阵列信号的空时稀疏表示模型,应用稀疏表示的匹配追踪算法和基追踪算法重构回波与混响的高分辨角度-多普勒像。并根据运动声呐回波与混响的空时分布规律及声呐待检测距离单元位置的先验信息,沿着混响空时分布脊线设计混响稀疏表示的专用空时导向向量字典,通过重构抗混响空时滤波器来抑制角度-多普勒平面的混响干扰。对运动声呐前视和侧视阵列的计算机仿真结果表明,在混响背景中,该方法采用声呐阵列单测量向量重构了低速运动目标多亮点回波的高分辨角度-多普勒像,频率分辨率突破傅里叶分辨率,角度分辨率突破阵列瑞利限,分辨率明显优于傅氏空时谱估计。      

海洋混响特性研究

海洋混响是海洋环境产生的回声。对于目标探测来说,混响是一种严重的干扰;对于大规模海洋生物探测及海洋环境遥感来说,海洋混响是其应用的基础。经过近一个世纪的理论和实验研究,深海混响的产生机理相对明确,基本的特性也较为清楚。浅海环境较深海环境复杂,目前浅海混响研究大多关注混响的平均特性,对其完整特性的研究将成为未来浅海混响特性研究的重点。文章对海洋混响的研究工作进行了综述,介绍了海洋混响的基本理论和应用。     

Application and measurement of underwater acoustic reciprocity transfer functions in reverberant sound field

The reciprocity measurement theory in anomalous reverberant sound fields was investigated.An improved method Was proposed due to the interrelated errors.The source volume velocity Was corrected by spatial average of measurement results and evaluation of the reverberant sound field influence on acoustic energy density.The result was validated in underwater experiment,corrected reciprocity measurement results were almost the same as direct measurement results.It indicates that reverberant sound field does not affect the validitv of the principle,but influences the obtainment of source volume velocity,then influences the measurement of transfer functions with the principle.The proposed method is simple and effective in anomalous reverberant sound fields.The study mav be valuable for the applications which are based on the principle.     

混响场中脉冲超声空化效应的研究

本文实验研究了不同脉冲宽度的８２０ｋＨｚ超声波的空化效应，结果得出，空化致自基产量随脉冲宽度及声强呈现规律性变化，尤其观察到了“脉冲空化峰”现象，本文从液面受迫振动角度出混响场中“脉冲空化峰”现象的机制。     

国际浅海声学会议取得圆满成功

首届国际浅海声学会议于4月21日一25日在北京召开，来自中、美、英、法、俄、日等17个国家和地区的130多位科学家参加了这次盛会。其中外国科学家近100名．浅海是经济活动最频繁的区域，渔业资源、石油天然气资源的利用和开发大都在浅海，各国之间海洋权益的冲突也主要集中在浅     

超声空化的电化学检测及混响场空化效应的研究

本文提出并设计了超声空化的电化学检测法，实现了通过分析样品的电学量变化来检测声空化，通过对混响场空化效应的研究，定性分析解释了混响场中空化饱和现象? ?