利用线性调频脉冲进行帧同步的方法及性能

针对水声信道的特点,提出了一种利用具有大的时宽带宽积的线性调频信号作为帧同步信号的方法。该方法首先在接收端进行滑动时频分析,从而实现线性调频信号的检测及粗同步,再进一步利用拷贝相关处理来实现细同步。计算机仿真和海上试验结果均表明,该方法能够在多途干扰下有效地实现同步。     

多波束测深声呐成像仿真及作用距离分析

AUV 等无人装备研制过程中如何选择合适的多波束测深系统以满足特定作业场景需求是工程技术人员关心的问题之一。从多波束测深声呐系统与 AUV 等无人系统的匹配角度出发，采用混响背景下的主动声呐方程建立了不同工作频率多波束作用距离计算评估方法，对 100 kHz~500 kHz 的多波束测深声呐作用距离进行了计算对比。在此基础上，采用线性调频、FFT 波束形成、脉冲压缩、样条插值扩充目标角度、Rife 算法优化角度估计技术，建立了多波束测深声呐的成像仿真方法，并通过直线地形、台阶地形对多波束测深声呐的成像特点和测深分辨率进行了分析。主要结论：1）建立了一种多波束作用距离评估的方法，可用于指导无人装备用多波束测深声呐频率参数的选型；2）建立的多波束测深声呐仿真办法可以帮助工程技术人员更直观地理解多波束测深声呐的成像特点；3）通过仿真分析了 CW 信号与线性调频信号下的距离分辨率，可用于指导波束测深作业时的高度、信号参数设置。     

基于分数阶傅里叶变换的水下目标速度估计

在高斯白噪声背景下,匹配滤波器作为线性调频信号的最优检测器,在水声信号处理中被广泛应用。 当发射信号为线性调频信号时,由水下目标径向速度引起的多普勒频移会造成回波和样本之间失配, 使匹配滤波器的检测性能下降,增加了目标速度估计的难度。 利用分数阶傅里叶变换对于线性调频信号的聚焦特性,提出了应用分数阶傅里叶变换的水下运动目标线性调频回波检测算法,完成对目标速度的估计, 推导目标运动速度与分数阶傅里叶变换阶数之间的关系,并对测量结果进行误差分析。 仿真测试表明,该算法可有效地估计混响背景下的目标径向速度,且具有良好的估计性能。     

MIMO高频地波雷达典型正交波形性能评价

理论研究表明,MIMO(Multiple-Input Multiple-Output)雷达技术能在很大程度上提高雷达系统的探测性能,而多个发射波形之间相互正交是实现此种改善的重要因素。为了确保正交波形在高频地波雷达系统上成功应用,本文结合地波雷达收发共址的特点选择了四种典型的正交波形,包括上调频与下调频线性调频中断连续波、错开时间的调频中断连续波、离散频率编码波形和线性调频脉冲的离散频率编码波形,分析了其应用于高频雷达时的模糊特性和互区模糊特性。通过对比分析四种波形的特征,指出利用恒定频率脉冲或线性频率调制脉冲构成的离散频率编码波形,采用优化算法优化频率编码序列后,表现出了较好的综合性能。     

一种猎雷声呐信号被动定向技术研究

介绍了一种猎雷声呐脉冲信号被动定位的测向方法。反猎水雷采用被动声自导方式,利用猎雷声呐发射的窄带脉冲信号,采用自适应 notch 滤波器估计信号的包络、频率、相位差。采用时延差粗测与相位差精测相结合的方法实现时延估计。此方法不仅对 CW 脉冲信号可测向、测距,还可适用于调频、跳频信号。 该方法已通过仿真及实测数据验证有效。     

基于火箭发动机的脉冲信号检测

水下火箭发动机工作时,尾部会产生高强度、宽频带背景噪声。在分析火箭发动机噪声产生机理和物理特性的基础上,主要研究了火箭发动机噪声背景下脉冲信号的检测流程和方法。采用自适应消噪和滤波,减弱背景噪声强度并提高了信噪比,建立了火箭发动机噪声背景下脉冲信号的检测方法,解决了强背景噪声脉冲信号难以检测的问题,为火箭发动机水下应用提供了新的思路。     

相位降噪与矢径分解组合的矢量序列分解方法

基于矢量序列相位与矢径的统计分布差异,本文提出一种TV (Total Variation)相位降噪和EMD (EmpiricalMode Decomposition)矢径分解组合的矢量序列降噪、分解方法。利用TV细致的演化特点进行相位降噪,其中引入最大信杂比准则,以优化选择调整参数和迭代次数;利用EMD适用于非线性非平稳分解的特点,将矢径分解为多个IMFS(Intrin-sic Mode Function),其中加入了非负判别,以保证重构矢量的相位不会发生跳变。然后,将降噪相位和分解的IMFS一一对应,重构矢量。考虑到历史继承性,该方法称为VEMD(Vector Empirical Mode Decomposition)方法。以高斯噪声污染的2个人工信号(线性调频信号、正弦+线性调频信号)和实测海杂波数据验证了本文所提出方法的性能。     

基于BP网络对模拟声呐信号分类

针对常规的主动声呐调查设备,在简单海洋分层模型的基础上,模拟了多波束类单频信号、侧扫类单频信号、Ch irp调频信号和混合信号4类声呐接收信号,并针对接收信号特征构造了3层BP网络模型,将隐藏层神经元数目设为可调节;利用时间域脉冲宽度和水深与频率域功率谱密度相结合的特征参量,成功地对模拟信号进行了分类。采用改进的BP网络模型,用训练成功的BP网络对102个检测信号进行了分类测试,结果表明,分类成功率较高,可达76%~84.6%,因而利用BP网络可以对不同类别设备的模拟声呐接收信号进行分类。     

基于图像处理的回声定位信号检测方法

鲸豚类海洋哺乳动物发出的回声定位信号是一种频率较高的短时脉冲信号,研究回声定位信号检测方法有助于快速、准确地检测海洋哺乳动物发声,进而更好地保护海洋哺乳动物.本文提出了一种基于图像处理的鲸豚类动物回声定位信号检测方法.该方法首先对收集到的数据进行分帧,计算每帧信号的时频图;使用Frangi滤波器对时频图进行滤波,以降低...     

声学方法进行海底沉物遥测分类：综述

本文讨论利用声学遥测方法进行海底沉积物分类的目的，用途及该项技术的发展背影和现状。重点介绍目前主要的用于浅，表层沉积物分类的声学遥测方法，包括选通等幅脉冲，宽频带脉冲，连续线性扫频脉冲等正入射方法和侧扫声呐，多波束测深等斜入射方法。     

Ocean surface current retrieval and imaging with a new shore-based X-band radar based on time-shifted up-and-down linear frequency modulated signal

This paper proposes a multifunction radar that can not only measure sea currents but also perform sea-surface imaging. The fundamental aspect of the proposed radar comprises transmitting time-shifted up-and-down continuous wave linear frequency modulated signals that allow for the offset of two one-dimensional range images of the sea surface that respectively correspond to the upward linear frequency modulated(LFM) signal and the downward LFM signal. Owing to the Doppler frequency shift from the sea surface, a range offset, which is proportional to the radial velocity of the sea surface, occurs between the upward and downward LFM signals. By using the least-squares linear fitting method in the transformed domain, the range offset can be measured and the current velocity can be retrieved. Finally, we verify the accuracy of current measurement with simulation results.     

AUV定位信号检测延时的蒙特卡洛模拟分析

在简要介绍AUV声学定位声纳接收机原理基础上,分析了CW脉冲信号在极性相关检测电路中的传输过程,建立了极性相关积分检测延时仿真分析模型。提出采用蒙特卡洛模拟方法获取检测延时的分布特征和统计参数的观点。实验结果表明蒙特卡洛模拟实验与硬件电路实验结果一致,对于解决随机性检测延时问题具有很强的能力。获得的结果可为AUV定位声纳检测门限的设定、声学测距和定位精度分析以及水声通信延时分析提供参考。     

由垂直入射脉冲和海底回波反演海底声参数

浅海海底声参数是影响声场传播的重要参量。文中根据信号的相位特性对反演稳定性的影响进行了数值模拟;并于2002年8月在黄海海区进行了海底声参数反演实验。利用垂直入射脉冲和海底回波数据进行海底声参数反演,由于海底回波信号随穿透深度增加而导致回波信号的信噪比降低,为了有效地增加海底声阻抗反演深度,提出平滑分段抽取冲激响应,重建声阻抗剖面的方法。结合Hamilton经验公式,分离海底声速、密度,反演结果与海底采样样本分析值、经验值吻合较好。     

A New Method for Matched Field Localization Based on Two-Hydrophone

The conventional matched field processing (MFP) uses large vertical arrays to locate an underwater acoustic target. However, the use of large vertical arrays increases equipment and computational cost, and causes some problems such as element failures, and array tilting to degrade the localization performance. In this paper, the matched field localization method using two-hydrophone is proposed for underwater acoustic pulse signals with an unknown emitted signal waveform. Using the received signal of hydrophones and the ocean channel pulse response which can be calculated from an acoustic propagation model, the spectral matrix of the emitted signal for different source locations can be estimated by employing the method of frequency domain least squares. The resulting spectral matrix of the emitted signal for every grid region is then multiplied by the ocean channel frequency response matrix to generate the spectral matrix of replica signal. Finally, the matched field localization using two-hydrophone for underwater acoustic pulse signals of an unknown emitted signal waveform can be estimated by comparing the difference between the spectral matrixes of the received signal and the replica signal. The simulated results from a shallow water environment for broadband signals demonstrate the significant localization performance of the proposed method. In addition, the localization accuracy in five different cases are analyzed by the simulation trial, and the results show that the proposed method has a sharp peak and low sidelobes, overcoming the problem of high sidelobes in the conventional MFP due to lack of the number of elements.     

Single hydrophone source localization

The method presented in this paper assumes that the received signal is a linear combination of delayed and attenuated uncorrelated replicas of the source emitted waveform. The set of delays and attenuations, together with the channel environmental conditions, provide sufficient information for determining the source location. If the transmission channel is assumed known, the source location can be estimated by matching the data with the acoustic field predicted by the model conditioned on the estimated delay set. This paper presents alternative techniques that do not directly attempt to estimate time delays from the data but, instead, estimate the subspace spanned by the delayed source signal paths. Source Localization is then done using a family of measures of the distance between that subspace and the subspace spanned by the replicas provided by the model. Results obtained on the INTIMATE'96 data set, in a shallow-water acoustic channel off the coast of Portugal, show that a sound source emitting a 300-800-Hz LFM sweep could effectively be localized in range or depth over an entire day     

由正入射遥测海底介质参数方法初探

通过数值模拟计算发现，对于分层有吸收海底，在层厚已知的条件下，除最下面的介质以外．有可能利用垂直入射的脉冲声波遥测各层的密度、声速与吸收系数。此法的要点是，根据入射波和层参数的假设值算得反射信号，与实际反射信号比较；然后改变参数再作计算，直到误差最小为止．此时对应的层参数即为介质参数值实际的估计值。指出根据这种方法有可能实现以自适应方法遥测分层海底的介质参数。     

Digital underwater acoustic voice communications

This paper describes the design of an underwater acoustic diver communication system controlled by a digital signal processor. The speech signal transmission rate is compressed by using linear predictive coding (LPC) and the extracted parameters are transmitted through the water to a synchronized receiver by employing digital pulse position modulation (DPPM). The pulse position in each time frame is estimated by an energy detection and decision algorithm which enables the received LPC parameters to be recovered and used to synthesize the speech signal