一种基于多普勒频移的被动合成孔径声纳探测方法*

由于自主小平台声纳孔径有限,对声纳探测的分辨率的提高有所限制。小平台的机动可以有效的与声纳探测方法相结合来提高声纳探测性能。针对这一特点,提出一种基于多普勒频移技术的被动合成孔径声纳探测方法。该方法根据自主小平台的机动所引起声纳的接收信号多普勒频移的变化,进行目标的频率与方位联合估计。本文将自主小平台的机动引入到波束形成技术当中形成一种新的被动合成孔径技术。数值仿真表明,该方法可以有效的进行目标方位估计,并且获得较高的方位分辨率,改善了自主小平台的探测性能。     

深海海底反射区声场角谱域分布结构分析及在声纳波束俯仰上的应用

深海海底反射区的声场干涉导致能量起伏,存在不连续的若干声纳可探测区.主动声纳探测海底反射区目标时,必须建立起声纳可探测区与波束俯仰角间的量化关系,通过合理选择最优发射波束俯仰角,才能使其对准声纳可探测区.本文通过理论分析和数值仿真,指出海底反射区离散的声纳可探测区的形成与不同掠射角声线能量周期性起伏直接相关,当主动声纳波束俯仰角与某个声线能量峰值对应的出射角一致时,可保证在一个对应的声纳可探测区内获得高的发射阵增益.在此基础上,通过声线干涉理论建立了声线能量峰值和出射角的量化关系,并提出一种脉冲串信号形式,包含多个可对准各声线能量峰值的子脉冲,每个子脉冲可保证照射到一个声纳可探测区,整个脉冲串发射时可在海底反射区的全部声纳可探测区内均取得高的发射阵增益.经仿真验证,该方法探测效果好,稳健性高,具有良好的应用前景.     

伪随机编码超宽带短脉冲的探测能力研究

 为进行弱信号检测，研究在脉冲雷达中获得大信号时间宽度与信号带宽积的方法，利用伪随机编码方法调制超宽带短脉冲，可以在保持子脉冲信号带宽的情况下，以低功率发射长脉冲串类噪声信号，而提高信号的能量，提高探测距离。通过仿真实验得出，利用伪随机编码技术可以使超宽带信号具有更强的探测能力，可以在回波信号功率水平远远小于噪声水平（如信噪比5%）的情况下实现对探测目标的高保真成像。     

主动声纳恒包络波形设计及其性能分析

为了解决伪随机编码调相信号峰均比过高问题,为主动声纳设计恒包络的伪随机编码MSK调制波形。通过分析MSK信号表达式,得到波形的复包络信号。使用遗传算法优化伪随机序列,降低波形的自相关旁瓣,可减小声纳的虚警概率。通过优化复包络信号的自相关函数旁瓣值和互相关函数值,得到自相关性能和正交性能优良的恒包络波形,可以缓解多部声纳间的同频干扰。通过仿真分析波形的模糊度图可知,波形具有良好的频率分辨率和距离分辨率。该波形设计可以取代峰均比过高的编码调相信号,满足主动声纳对运动目标的探测需求。     

水下窄脉冲超宽带信号的传播特性仿真

超宽带信号具有分辨率高、截获概率低、穿透能力强等优点,将在水下目标探测、定位及通信等领域具有良好的应用前景。基于水下等离子体声源提出了窄脉冲超宽带信号产生方法,建立了以传播损失和海洋环境噪声为主要影响因素的超宽带脉冲传播信道模型;结合湖试实测数据,利用Matlab仿真软件和Welch谱分析法,仿真分析了不同频率的超宽带脉冲在水下传播不同距离后的功率谱密度以及传播特性。研究成果对水下等离子体超宽带脉冲的工程应用具有重要的参考价值,同时对水下等离子体超宽带脉冲声源的设计和研制也有一定的借鉴意义。     

海豚等动物神经系统处理多普勒信号的一种可能性方案

海豚、蝙蝠等动物具有功能强大的生物声纳，生物神经系统处理多普勒效应的网络结构可能会有多种形式.对这类生物的神经系统信号处理机制及结构的研究，将能为信息处理提供新的视角.根据序空间神经编码理论，构建了一个生物神经回路处理多普勒信号.经计算机仿真可知，该生物神经网络运算速度快、分辨率高，并能处理任意的连续变频率多普勒信号.所研究的仅由1—2个神经元组成的网络结构是最简单的，由于网络只有一级神经元的延时，保证了处理的快速性，在神经元输出10个脉冲的情况下分辨率可达7^-10. 关键词： 多普勒效应 海豚 神经编码 神经脉冲序列     

Hilbert-Huang变换分析THz脉冲信号的时频特性

提出一种基于Hilbert-Huang变换的THz时域光谱分析方法,将THz时域脉冲信号分解成有限数目的单分量信号之和,利用Hilbert变换求得瞬时频率来获得幅值的时频分布——Hilbert-Huang变换谱,实现了通过水蒸气的THz脉冲信号的时频分析,揭示了THz波与水蒸气相互作用的频谱时域分布特性,并与基于小波变换的时频图进行了对比分析。结果表明,该方法可以同时提高THz脉冲时频分布的时间分辨率和频率分辨率,具有局部化分析和自适应选择的特点,还能直观地表现出各频率成分之间的相对时间延迟。     

高频共振预探测多脉冲激光测距方法

在无合作目标激光测距中,提出了一种高频共振预探测和多脉冲相关处理对远目标距离进行高精度测量的技术方案.脉冲回波光电流信号经高频共振预探测电路进行放大滤波处理并转换为包含高精度定时特征点的高信噪比的双极性衰减振荡脉冲信号;之后利用多脉冲相关处理构造出的新脉冲函数进一步改善其信噪比.理论计算结果表明:最小可探测光脉冲电流仅为17 nA,与直接探测脉冲方法相比信噪比可提高60倍;在回波光电流脉冲峰值1:10000的动态范围内,走离误差小于0.1 ps.根据此原理研制出了脉冲激光测距仪,仪器在激光发射平均功率约为1 mW时,无合作目标测程大于2000 m,在1.5—300 m范围内测距精度达到±(3 mm+2 ppm),远目标测距精度为±(10 mm+10 ppm).该测距仪系统已用于全站仪产品中.     

单光束扩束扫描激光周视探测系统参数对探测能力的影响

针对现有单光束激光同步扫描周视探测对脉冲重复频率要求较高,难以实际应用的问题,提出单光束扩束扫描激光周视探测方法.基于单光束扩束扫描激光周视探测工作原理,推导了最低扫描频率和脉冲频率解析式;分析了圆柱目标回波特性及关键参数截面衰减系数,建立了脉冲扩束激光圆柱目标回波功率数学模型,讨论了系统参数对截面衰减系数的影响,得到最大相邻脉冲光束夹角表达式;重点分析了脉冲频率、光束角和光束入射角对不同直径目标的探测能力的影响;得到了探测系统对典型条件下最大光束角、最低脉冲频率的计算方法.结果表明,对扫描光束稍加扩束可有效降低脉冲重复频率要求.研究结果可为单光束脉冲激光周视探测系统设计、优化提供理论依据.     

基于改进强耦合振子的微弱脉冲信号检测方法

强耦合振子可用于微弱脉冲信号的检测和波形恢复,但其对微弱脉冲信号的检测频率会受到系统内置频率的限制.在系统内置频率固定的情况下,系统只能对一定频率范围内的脉冲信号进行有效检测和波形恢复,在检测更高频率的脉冲信号时会出现波形失真.本文分析了耦合振子内置频率和微弱脉冲信号检测频率之间的关系,提出两种改进强耦合振子结构以扩展微弱脉冲信号的频率检测范围.通过引入非线性恢复力耦合项,非线性恢复力强耦合振子可以有效保留信号的高频分量,在更高频率的脉冲信号输入时也能较好地保留信号特征.双振子强耦合系统通过引入Van der Pol-Duffing振子,加强了系统内部结构的稳定性,同样达到了扩展脉冲信号频率检测范围的效果.此外,基于变迭代步长和混沌检测的频率相关性,提出了一个未知频率脉冲信号检测方法,以改变迭代步长的方法代替改变系统内置频率来进行频率扫描,并且利用混沌检测的频率相关性,将接收信号和恢复信号的相关系数和纯噪声输入情况下的相关系数进行对比,根据两个相关系数之间的明显差异可以有效检测出脉冲信号.通过仿真实验进行验证,所提方法可以有效检测出未知频率的脉冲信号,并且所提的改进强耦合振子结构相对于...     

An echolocation visualization and interface system for dolphin research

The present study describes the development and testing of a tool for dolphin research. This tool was able to visualize the dolphin echolocation signals as well as function as an acoustically operated "touch screen." The system consisted of a matrix of hydrophones attached to a semitransparent screen, which was lowered in front of an underwater acrylic panel in a dolphin pool. When a dolphin aimed its sonar beam at the screen, the hydrophones measured the received sound pressure levels. These hydrophone signals were then transferred to a computer where they were translated into a video image that corresponds to the dynamic sound pressure variations in the sonar beam and the location of the beam axis. There was a continuous projection of the image back onto the hydrophone matrix screen, giving the dolphin an immediate visual feedback to its sonar output. The system offers a whole new experimental methodology in dolphin research and since it is software-based, many different kinds of scientific questions can be addressed. The results were promising and motivate further development of the system and studies of sonar and cognitive abilities of dolphins.     

Intrinsic echolocation capability of Hector's dolphin, Cephalorhynchus hectori.

A sonar system's echolocation capabilities can be inferred from the ambiguity distribution (defined here in terms of the conventional signal response function) of each of its transmitted signals. Several records of sounds emitted by Hector's dolphin are analyzed. The computed ambiguity distributions indicate that the sonar clicks of Hector's dolphins should be capable of resolving the ranges of targets as close together as 2 cm apart, but that target velocities cannot be resolved to any useful degree from a single echo.     

Bio-inspired wideband sonar signals based on observations of the bottlenose dolphin (Tursiops truncatus)

This paper uses advanced time-frequency signal analysis techniques to generate new models for bio-inspired sonar signals. The inspiration comes from the analysis of bottlenose dolphin clicks. These pulses are very short duration, between 50 and 80 micros, but for certain examples we can delineate a double down-chirp structure using fractional Fourier methods. The majority of clicks have energy distributed between two main frequency bands with the higher frequencies delayed in time by 5-20 micros. Signal syntheses using a multiple chirp model based on these observations are able to reproduce much of the spectral variation seen in earlier studies on natural dolphin echolocation pulses. Six synthetic signals are generated and used to drive the dolphin based sonar (DBS) developed through the Biosonar Program office at the SPAWAR Systems Center, San Diego, CA. Analyses of the detailed echo structure for these pulses ensonifying two solid copper spherical targets indicate differences in discriminatory potential between the signals. It is suggested that target discrimination could be improved through the transmission of a signal packet in which the chirp structure is varied between pulses. Evidence that dolphins may use such a strategy themselves comes from observations of variations in the transmissions of dolphins carrying out target detection and identification tasks.     

任意复包络信号的匀速运动目标回波脉间补偿及相干积累

现代声呐、水下制导等水声探测系统常常使用窄带脉冲、调制、编码、伪随机等种类繁多的发射信号波形来满足低信噪比检测、高分辨估计、抗干扰、主动隐蔽探测的应用需求.针对这一情况,本文研究了任意信号的长时间积累问题,给出了一种任意复包络信号的匀速运动目标回波脉间补偿及相干积累检测方法.通过构建任意发射信号波形的广义模糊函数,将匹配滤波器输出表示为所构造的广义模糊函数,使得任意复包络信号的脉压波形不仅能够用统一的数学模型来表述和计算,而且能够提供多脉冲回波的距离走动信息和多普勒频移信息,为多脉冲距离位置对齐和Fourier变换(FFT)积累提供了依据.对于用广义模糊函数表示的匹配滤波器输出,采用Keystone变换将复包络对齐,消除了距离走动,采用FFT补偿多普勒频移项,实现了任意复包络信号的长时间相干积累.对于水下探测中使用的连续波信号、线性调频信号以及复杂的m序列编码信号、Costas跳频编码信号波形进行了信号积累及检测的计算机仿真,验证了任意复包络信号的匀速运动目标回波脉间补偿及相干积累的正确性.消声水池实验验证了该方法的有效性.     

宽带参量阵技术在近海探测中的研究

文章针对非线性声学宽带参量阵技术应用于近海海底剖面绘制及掩埋物探测进行了分析研究。对于宽带参量阵声呐产生的差频信号利用Berktay包络解调理论和KZK(Khokhlov-Zabolotskaya-Kuznetsov)方程,对其进行了理论分析,水池实验研究和时域数值模拟,并结合声呐方程计算,说明该技术用于近海探测的可行性。本文同时结合脉冲压缩技术对产生的宽带差频信号做匹配处理,用于提高设备的垂直分辨率。最后在海试实验中,利用文中设计的参量阵声呐,分别使用宽带差频信号和单频差频信号对浅海海底沉积层和海底掩埋管线进行探测,取得了清晰的剖面图和掩埋物探测结果,验证了宽带参量阵技术在海底探测中的有效性和实用性。      

声呐员听音移频操作客观规律研究*

声呐员在听音过程中,可以对收听到的声音进行移频操作,通过这一操作,声呐员可以将信号调制到自己认为合适的频段以便检测识别信号,而移频的具体频段没有定量的参考依据,这使声呐员移频操作较为盲目。本文从心理声学的角度对声呐员的移频操作进行研究,给出了移频前后信号的响度差值的变化规律和信号尖锐度的变化规律。研究结果表明,经过移频操作,响度移频前后在2000-5000 Hz左右存在最大值,而尖锐度随着移频频率和信号的频率的升高而升高,本文所得出的结论可为声呐员对舰船辐射噪声被动听音移频操作提供参考依据。     

Evidence of high-frequency acoustic emissions from the white-beaked dolphin (Lagenorhynchus albirostris)

Recordings of the signals from a school of white-beaked dolphins show that the frequency of their acoustic emissions extends to at least 305 kHz. These signals were detected by a sector scanning sonar used as a passive listening device of high bearing and time resolution. The records contain three types of signal, one of high intensity, one of a variable high repetition rate, and another showing a time-varying effect. Acoustic signals radiated by dolphins have been recorded and studied over a long period of time by many investigators. The purpose of this letter is to report evidence that acoustic emissions from white-beaked dolphins have significant energy at frequencies around 305 kHz, about one octave higher than previously observed. The observations discussed here were made aboard the fisheries research vessel CLIONE in the Wellbank flat area of the southern North Sea on 13 June 1970 between 1040 and 1110 h. When the dolphin signals were observed, the transmitter of the sector-scanning sonar in use was turned off, and the system was utilized as a passive listening device of high bearing and time resolution.     

傅里叶望远镜部分周期信号解调及对成像的影响

为了解决傅里叶望远镜高功率短脉宽激光只能包含部分周期信号的难题,本文提出多脉冲拼接技术并对其基本原理和应用范围进行深入研究.首先介绍高功率短脉宽激光与声光移频器移频带宽之间的矛盾,进而引出利用傅里叶望远镜传统时间解调公式进行部分周期信号解调存在的困难.然后给出多脉冲拼接技术的基本理论,推导出理想情况下移频频率、脉冲重复率和脉宽满足的拼接条件.进而详细分析移频频率稳定性和脉冲重复率稳定性对多脉冲拼接成像结果的影响,并通过计算机仿真研究一般情况下脉宽变化对多脉冲拼接成像结果的影响.最后得出移频频率和脉冲重复率对成像无影响,激光脉宽变化小于25%仍可识别目标轮廓的结论.     

Insights into dolphin sonar discrimination capabilities from human listening experiments

A variety of dolphin sonar discrimination experiments have been conducted, yet little is known about the cues utilized by dolphins in making fine target discriminations. In order to gain insights on cues available to echolocating dolphins, sonar discrimination experiments were conducted with human subjects using the same targets employed in dolphin experiments. When digital recordings of echoes from targets ensonified with a dolphinlike signal were played back at a slower rate to human subjects, they could also make fine target discriminations under controlled laboratory conditions about as well as dolphins under less controlled conditions. Subjects reported that time-separation-pitch and duration cues were important. They also reported that low-amplitude echo components 32 dB below the maximum echo component were usable. The signal-to-noise ratio had to be greater than 10 dB above the detection threshold for simple discrimination and 30 dB for difficult discrimination. Except for two cases in which spectral cues in the form of "click pitch" were important, subjects indicated that time-domain rather than frequency-domain processing seemed to be more relevant in analyzing the echoes.