采用格拉斯曼流型的深海单帧基混响抑制方法

提出了一种混响抑制方法以抑制深海环境中的混响干扰。基于时空谱矩阵中信号(混响和目标)旁瓣的低秩性与主瓣的稀疏性差异,将混响抑制问题建模为矩阵的低秩、稀疏和扰动三项分解。采用格拉斯曼流型计算混响低秩空间,并对稀疏矩阵稀疏性进行约束,提出了一种混响快速抑制方法。基于随机正交模型与随机稀疏模型仿真分析了所提方法的有效性。结合南海实测深海混响数据和目标仿真信号对所提方法的有效性进行了实验验证。结果表明,与已有的序列随机投影子空间追踪与稀疏滤波(SRPSS)方法相比,所提方法的混响抑制性能相似,但耗时减少可达55%。

波束形成后多干扰抵消方法

为解决常规波束形成后干扰抵消方法仅能从目标波束内消除一个干扰影响的局限性,提出了一种可实现多干扰抑制的波束形成后干扰抵消方法,用于解决多干扰条件下的弱目标波束形成问题.该方法通过最小化多个干扰波束对目标波束的影响,获得用于抵消干扰波束的加权值;然后从目标波束中减去加权后的干扰波束,从而获得抑制干扰后的目标波束。该方法继承了常规波束形成方法的稳健性,因此在阵列流型失配等存在误差的条件下可以用于目标波束形成。仿真和海上实验数据表明,与最小方差无失真响应方法和解卷积的常规波束形成方法相比,该方法可以有效抑制干扰的影响,且当目标与任一干扰方位相近时,其方位谱中可以观察到目标波束,而另外两种方法的目标波束均被干扰波束或其旁瓣所掩盖;与设置凹槽的波束图综合方法相比,该方法算法复杂度低,计算速度快,稳健性更好。

海洋声学信息感知实验室海洋声学实验与人才培养

海洋是我国经济社会发展的重要战略空间。该文在海洋强国战略背景下探讨国防发展对深远海领域的建设需求,以海洋声学信息感知重点实验室建设为例,结合多次海洋声学海上实验实践,从实验室构架、海上实验组织管理和学生培养等维度,探讨高校实验室在科技创新及人才培养中发挥的重要作用。通过近5年的建设,实验室定位明确,发展思路不断拓宽,在高校"双一流"建设中发挥了积极作用。

南海南部海域深海环境噪声统计特性分析

针对海洋噪声对声呐信号处理和声呐性能评估的背景干扰问题,本文分析了南海南部海域夏季和冬季实测深海环境噪声的深度分布、经验拟合和概率密度分布等统计特性;利用参数化模型得到了噪声谱曲线及其与风速、波高、1 kHz谱之间的经验拟合结果;提出了基于Weibull和Burr分布噪声谱级概率密度拟合方法。结果表明:400 Hz以下800 m以浅夏季噪声谱级中值比冬季高约6 dB,低频航船噪声谱级概率密度(PDF)服从Burr分布,高频风关噪声PDF近似服从高斯分布,夏冬两季噪声统计特性差异与中尺度涡旋分布、声信道传播损失和航船噪声源密度密切相关。

自适应直达波抑制方法在前向散射宽带信号中的应用

介绍了前向声散射目标探测的基本原理,并提出了基于自适应滤波的直达波抑制（DBS-AF）方法。将DBS-AF方法扩展到线性调频（LFM）信号中,把信号的包络视为一种广义＂波形＂并输入自适应滤波器。利用该方法分析了湖试数据,并得到了随观测时间变化的检测输出曲线。在曲线上直达波对应了曲线的背景输出而目标引起的接收声场畸变则对应了曲线的峰值起伏。单个通道的直达波抑制效果可以达到-5 dB左右;引入去均值化预处理能够增强直达波抑制效果,再利用多通道的接收信息,直达波被抑制到-10 dB以下。影响算法性能的主要因素是训练权值时段内接收信号的起伏和信直比。

深海本地界面混响平均强度模型与规律分析

为揭示深海多途传播效应及界面参数对本地界面混响强度的影响规律,将界面混响表述为不同多途混响衰落过程的非相干叠加结果,并结合界面散射的若干物理机制,建立了以海面海底物理参数为变量的混响强度模型.通过数值仿真和理论分析研究了不同多途混响强度的衰落特性、到达角的空间分布及部分物理参数对混响强度的影响,并利用南海海盆(典型泥质海底)实验数据对模型有效性进行验证.仿真结果表明,界面混响强度随时间变化呈现多峰结构,峰值时间与多途混响的到达时间分布一致。声源与接收器均位于近海面处时,首峰的峰值强度及其衰落过程由海面风速决定,其它峰的峰值强度由海面海底参数共同决定,但其衰落过程主要受到底质参数的影响.

部分范数约束的稀疏恢复算法及其在单载波水声数据遥测中的应用

对于单载波水声数据压缩与恢复问题,压缩感知能以较低能耗获得信号压缩与恢复效果。但压缩感知核心目标是直接求最小l_0范数,该问题表现为NP难问题,因此,常将其转化为求l_1范数约束最小化问题,而求l_1范数约束最小化的稀疏解精度有限。基于此,推导出基于部分范数约束的稀疏信号恢复算法,该算法通过部分范数约束在拉格朗日求解中增加一个零吸引项,从而动态分配稀疏抽头的软阈值。同时,该算法用于实际海上数据的遥测,结合离散余弦变换(DCT),可将单载波水声数据恢复精度提高。

改进的稀疏度自适应多路径匹配追踪算法

在信号重构算法中,针对基于树的多路径匹配追踪深度优先算法计算量大和多路径匹配追踪信号稀疏度未知等问题,本文提出了一种改进的稀疏度自适应多路径匹配追踪算法。该算法将自适应思想引入多路径匹配追踪算法中,自适应选择支撑集原子个数,并利用剪枝技术选择原子匹配概率最大的路径,使算法搜索路径更为有效,且大大降低了计算量。该算法改进了内积匹配准则,能在测量矩阵中更准确高效地挑选与残差信号匹配的原子,并在迭代过程中采用支撑集原子回溯和指数变步长方法提高重构精度。与传统MMP算法相比,本文提出的算法运算时间短,重建精度高,更具有实际应用价值。

基于矢量传声器阵列的低频声源定位

矢量传声器由传统的声压传感器和三维振速传感器组成,提供了更加完备的声场信息,理论上具有不随频率变化的空间指向性,为小孔径阵列定位低频声源提供了可能。为了实现小孔径阵列低频声源的精确定位,提出了矢量传声器频域校准合成孔径和稀疏表示定位相结合的方法。该方法采用固定点声压传声器来校准阵列不同位置时声源初始相位信息的方式实现阵列孔径虚拟扩大,该方法易于工程实现,在频域进行校准可以减小不同频率之间的交叉项干扰,将频域校准合成孔径与稀疏表示定位方法相结合可以进一步提高低频分辨率和降低定位误差,仿真验证了该方法的有效性。

A study of the mixed layer of the South China Sea based on the multiple linear regression

Multiple linear regression （MLR） method was applied to quantify the effects of the net heat flux （NHF）, the net freshwater flux （NFF） and the wind stress on the mixed layer depth （MLD） of the South China Sea （SCS） based on the simple ocean data assimilation （SODA） dataset. The spatio-temporal distributions of the MLD, the buoyancy flux （combining the NHF and the NFF） and the wind stress of the SCS were presented. Then using an oceanic vertical mixing model, the MLD after a certain time under the same initial conditions but various pairs of boundary conditions （the three factors） was simulated. Applying the MLR method to the results, regression equations which modeling the relationship between the simulated MLD and the three factors were calculated. The equations indicate that when the NHF was negative, it was the primary driver of the mixed layer deepening; and when the NHF was positive, the wind stress played a more important role than that of the NHF while the NFF had the least effect. When the NHF was positive, the relative quantitative effects of the wind stress, the NHF, and the NFF were about i0, 6 and 2. The above conclusions were applied to explaining the spatio-temporal distributions of the MLD in the SCS and thus proved to be valid.

On analyzing space-time distribution of evaporation duct height over the global ocean

The statistical features of the evaporation duct over the global ocean were comprehensively investigated with reanalysis data sets from the National Centers for Environmental Prediction. These data sets have time and spatial resolutions of 1 h and 0.313°x0.312°, respectively. The efficiency of the analysis was evaluated by processing weather buoy data from the Pacific Ocean and measuring propagation loss in the Yellow Sea of China. The distribution features of evaporation duct height （EDH） and the related meteorological factors for different seas were analyzed. The global EDH is generally high and demonstrates a latitudinal distribution for oceans at low latitudes. The average EDH is approximately 11 m over oceans beside the equator with a latitude of less than 20°. The reasons for the formation of the global EDH features were also analyzed for different sea areas.

区域蒸发波导及微波路径损耗预报与验证

蒸发波导对近海面电磁波传播有重要影响,区域蒸发波导及微波路径损耗预报对评估海上雷达、通信、侦察等电磁系统的性能至关重要.本文基于美国国家环境预报中心的GFS预报产品和NAVSLaM蒸发波导预测模型,对我国南海海域进行了大面积蒸发波导预报,利用欧洲中期天气预报中心发布的ERA5再分析数据进行了对比,并结合电磁波传播抛物方程模型开展了微波在蒸发波导信道中的路径损耗预报;然后利用在南海北部的路径损耗测试链路,对预报结果的准确性及时效性进行了验证.再分析数据对比及海上试验验证结果表明,基于GFS数据开展的蒸发波导层中路径损耗预报,除个别异常点外,预报的路径损耗与实测值趋势相同,在前24 h结果与实测值较为吻合,误差在5〜10 dB,可以用于大面积蒸发波导层中路径损耗的预报.另外,试验发现,降雨会导致预报结果与实测数据有很大的误差,在进行电磁波传播计算时,应充分考虑雨衰、海面粗糙等海洋环境.

近似零伪范数约束的水声信号压缩与重构

提出近似零伪范数约束的稀疏压缩与重构方法。该方法首先采用稀疏二进制矩阵作为测量矩阵,对信号进行压缩和传输;在接收端仅给定测量矩阵和压缩信号的条件下,采用小波滤波器设计字典,利用最陡梯度法寻优和投影方法求得信号的稀疏表达,最终结合稀疏表达值与字典用于水声数据重建,海试实验结合扫频以及单载频信号进行处理,采用NMSE、SNR以及算法运行时间作为算法的评估指标,以验证本文方法相对于传统算法在恢复精度上的提高。

Impact of Evaporation Duct on Electromagnetic Wave Propagation During a Typhoon

The evaporation duct,a result of evaporation from the ocean,is a region above the sea surface in which radio waves are refracted downward.This duct has strong effects on microwave instruments.Typhoons cause huge anomalies in marine meteorological parameters that influence the evaporation duct distribution and structure,which in turn affects the propagation of electromagnetic(EM)waves.However,EM wave propagation under the typhoon process has seldom been reported.Thus,taking Typhoon Phanfone(201929)as an example,this study uses a dataset from the European Centre for Medium-Range Weather Forecasts,combined with the Naval Atmospheric Vertical Surface Layer Model and the parabolic equation model,to study the evaporation duct’s impact on EM wave propagation during a typhoon.The spatial and temporal path loss distributions reveal that large amounts of EM wave energy are emitted from the evaporation duct when the EM wave passes through a typhoon eye.On average,a typhoon eye causes an approximately 20 dB increase in path loss for EM wave propagation at low antenna height.Furthermore,the effects of a typhoon eye on EM wave propagation at different signal frequencies and antenna heights are studied.The results show that a typhoon has a larger impact on EM wave propagation with low signal frequency and high antenna height.

Underwater Noise Target Recognition Based on Sparse Adversarial Co-Training Model with Vertical Line Array

The automatic identification of underwater noncooperative targets without label records remains an arduous task considering the marine noise interference and the shortage of labeled samples.In particular,the data-driven mechanism of deep learning cannot identify false samples,aggravating the difficulty in noncooperative underwater target recognition.A semi-supervised ensemble framework based on vertical line array fusion and the sparse adversarial co-training algorithm is proposed to identify noncooperative targets effectively.The sound field cross-correlation compression(SCC)feature is developed to reduce noise and computational redundancy.Starting from an incomplete dataset,a joint adversarial autoencoder is constructed to extract the sparse features with source depth sensitivity,aiming to discover the unknown underwater targets.The adversarial prediction label is converted to initialize the joint co-forest,whose evaluation function is optimized by introducing adaptive confidence.The experiments prove the strong denoising performance,low mean square error,and high separability of SCC features.Compared with several state-of-the-art approaches,the numerical results illustrate the superiorities of the proposed method due to feature compression,secondary recognition,and decision fusion.

深海声传播信道和目标被动定位研究现状

随着我国海洋技术逐渐从近浅海向深远海的战略性转移,深海目标远程探测技术逐渐受到重视。海洋中目前已知的可用于远距离传播的信号是声信号,海洋是"声透明"的。基于水声传播特性的新型水声技术是实现装备探测能力突破的关键。文章主要概述了目前研究比较集中的深海表面波导、表面波导泄露、会聚区、海底弹射和可靠声路径5种深海声传播信道,以及基于可靠声路径的目标被动定位方法。旨在通过梳理深海声传播规律及相关被动定位技术,为水声技术的快速发展提供思路。

Forward acoustic scattering by moving objects:Theory and experiment

The normal mode model for scattering in shallow water is employed to investigate the forward scattering with a target crossing the source-receiver axial line. An experiment was conducted in a littoral environment to analyze forward scattering by a slowly moving object. The theoretical and experimental results show that the sound field aberration takes minimum values if the object is located mid-point along the source-receiver line, whereas it attains its maximum if the object is close to the source or receiver. The total field is either enhanced or suppressed if the object crosses different Fresnel zones. In addition, the duration of shad- ow-induced aberration is dependent on the width of the first Fresnel zone, which is longest at the mid-point of the source-receiver line.

Matched field noise suppression: Principle with application to towed hydrophone line array

Discrete noise source suppression in underwa-ter acoustic channel has attracted great attention in recent years. The paper proposes a new principle for dealing with the problem. This new principle is called matched field noise suppression (MFNS). Based on a previous work of the au-thors group, a full understanding about how a discrete noise source shows effects on the performance of a towed hydro-phone line array has been obtained. In light of that finding, MFNS is proposed, which explores and utilizes the charac-teristics of the noise transmission channel to achieve much greater suppression of the noise in comparison with existing approaches. MFNS combines the concept of matched field processing (MFP) and optimal sensor array processing (OSAP) together to suppress the discrete noise source and to maintain an optimal beam for receiving far-field wanted plane wave signals. A MFNS beam-former is deduced in constraint with signal plane-wave response being unit and noise matched field response being zero. A closed-form solution of the weight vec-tor for the beam-former is given. Computer simulation results agree well to the theoretical analysis.

Tracking-positioning of sound speed profiles and moving acoustic source in shallow water

An ensemble Kalman filter（EnKF） approach is proposed to perform sequential tracking of water column sound speed profile（SSP） using a moving acoustic source. First,the SSPs are discretized in depth and range, and are expressed by the empirical orthogonal functions（EOFs）. Second, the acoustic source state information and the first three orders of EOF coefficients are expressed as the state variable, and the acoustic field information received by the vertical line array are the measured values. Successively, the state variables and measured values are used to establish the state-measure model. Last, the EnKF is utilized to track the state variables. The simulation results show that the root mean square error of SSP and the absolute error of source are all small, and thus the acoustic source tracking-positioning has high accuracy. Moreover, increasing the number of sample collection, the signal-to-noise ratio and the number of receiving elements can improve the tracking-positioning results. The method is verified using the experimental data of the East China Sea.

Application of the direct blast adaptive suppression method to the forward scattered broadband signals

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.