东海PN断面黑潮区域海底起伏对声传播的影响

利用2001年3月东海PN断面“973”调查获得的CTD数据，用数值模拟方法研究了PN断面黑潮区域海底起伏对声传播的影响。由深水区向浅水区传播，随着海底的抬升声线的海底反射和海面反射次数增加，声强衰减更快，限制声传播距离。由浅水区向深水区传播，随着海底降低声线上反转点深度增加，传播一定距离后部分声线不能到达上层水体，于是声强衰减也增快。     

北极冰下声传播特性实验研究

通过2017年8月6日在北极海域开展的一次声传播实验,开展了冰下声传播特性实验研究。结合Burke-Twersky （BT）散射模型与射线模型,分析了冰下声传播的多途到达结构,研究了接收声强变化规律,解释了接收声强在30 min内衰减20 dB的现象,分析了接收信号的时间相关性,探讨了接收信号相关性较低的原因。实验结果表明,表面接收信号主要由小角度多次反转反射声线、一次海底反射声线和二次海底反射声线依次构成,表面声道到达信号显著强于海底反射信号。试验冰站在试验期间的运动导致了声传播信号强度和相关性的迅速衰减,并通过仿真得到了验证。     

东海PN断面黑潮区域声传播数值模拟

利用BELLHOP声学模式模拟东海PN断面黑湖区域的声传播，比较夏季和冬季的接收信号。冬季的声速小于夏季的声速，但是信号到达时间小于夏季的到达时间，分析表明冬季的声速梯度小于夏季声速梯度，声线的海面反射次和海底反射次数小于夏季，声线的路程短，声线路程对到达时间的影响超过声速的影响，于是冬季信号早于夏季到达。     

海洋声速起伏对声传播及定位精度影响分析

海洋中声速起伏导致水声信道发生变化,进而引起声线到达结构的变化,对水声传播及定位精度产生一定影响。为讨论这一效应,基于TDOA体制建立了考虑声线弯曲的水下目标无源定位模型,分析了声速起伏对水下声传播路径及传播时间的影响,进而研究了声速起伏对水下无源定位测量精度影响程度。结果表明:当水平传播距离较大时,声速剖面起伏对声传播路径及传播时间的影响更为显著;以典型四元阵为例,若基线长度为20 km,接收阵位于水下5 km处,在不考虑其它随机误差影响下,海洋声速起伏造成的声源定位误差量级在0.5 m以内。分析结果有助于更好地利用环境特征优化无源定位测量方案,可为高精度水下无源定位系统设计及精度评估提供依据。     

声跃层控制声线传播弯曲模型的构建

基于斯涅耳折射定律,将海水垂向等分成若干层,利用傅里叶步近算法,构建受声速剖面唯一控制的声线传播弯曲模型。将该模型用于模拟研究不同浅海声跃层类型对声线传播弯曲的影响,得出声线波长和轨迹长度按负跃层、无跃层、正跃层的顺序逐渐增加。并利用该模型定量研究跃层深度、跃层强度、跃层厚度三特征参量对声线传播弯曲的影响,得出负跃层强度越大、厚度越大、深度越浅,声线弯曲越大,波长越小。正跃层三特征参量对声线作用相反。     

深海汇聚区的焦散结构与声能分布特征

在深海汇聚区声场中,不同初始角的声线在传播过程中因折射程度差异形成特定的焦散结构。根据射线理论推导了线性剖面条件下用F算子表示的声线轨迹模型,并讨论了焦散结构与掠射角及声源-接收深度配置的变化关系。折射型焦散线由0°~5°的小角度声线构成,为波导结构;反射型焦散线由掠射角为±(5°~10°)的声线构成,为折线结构,且上行与下行声线的焦散线结构明显不同。应用BELLHOP模型分析得出了汇聚区增益与声源-接收深度条件的变化关系,并根据射线到达结构和焦散特征提出了一种确定汇聚区位置和范围的方法。     

由远程声传播估算海洋pH值的一种方法

海洋中的低频(<1000Hz)声吸收主要决定于海洋的pH值.虽然测得的远程(1000km量级)声传播的绝对幅度相当复杂地依赖于海洋的介质和环境参数,但对不同频率间的相对吸收差的测量能给出有用的信息.此外,沿海面反射声线(RSR)的传播衰减还应附加上海面散射引起的损失.原则上通过比较发射和接收到的声信号的频谱能估算海洋的pH值和表面粗糙度.我们分析了北太平洋750km声传播实验的部分数据.实验结果与理论估算定性地相符,但其测量精度还不足以进行定量的比较(该实验并不是为测量相对吸收差而设计的).估算表明,为了获得0.05的pH测量精度,当信号频率为550±100Hz,传播距离为750km时,对北太平洋(pH≈7.7)和大西洋(pH≈8.0)海域分别需要对100和60个独立测量样本进行平均以消除内波及噪声引起的幅度谱畸变.     

拖曳声源深海传播损失算法改进

为实现水声传播损失高效准确计算,以满足工程应用要求,基于南海某深水海域水声调查数据研究改进拖曳声源深海传播损失算法。首先,对信号时间序列分析发现:深海多途传播结构显著,可分为直达波、第一二次海底反射波,信号幅度逐渐减小,海面反射波与直达波重叠;目标信号中心频率产生多普勒频移,与声源拖曳速度对应较好;"单频"正弦信号并非单一频点上的声信号,为一窄带功率谱,谱峰对应信号中心频率。进而,从信号识别及多途效应处理两方面对算法进行改进:基于功率谱频带分布,设计Butterworth滤波器带通截止频率,从频域上滤除噪声信号;依据环境噪声电压幅值,制定其判定标准,从时域剔除与目标信号同频带噪声信号。算法改进后可较好适应低信噪比环境下多途拖曳声源信号能量计算,快速高精度得到传损失数据。     

中尺度涡条件下的深海声场效应研究

通过构建中尺度涡的数学模型,利用射线-简正波-抛物方程(RMPE)声学模型进行传播损失计算,进而分析在深海声道、深海会聚区、海底反射3种传播模式下,中尺度涡对深海声效应的影响。数值仿真结果显示,暖涡对深海声道、会聚区产生下压效果,使会聚区水平距离变大,深海声道深度方向上变宽;冷涡使会聚区上抬,距离变短,对声场散射现象明显。研究结果表明,涡旋环境条件下,声场特征会产生显著变化。试验结果揭示了中尺度涡对深海声场效应的影响,对指导海上运用中尺度涡现象开展的科学研究、工程实践、军事运用具有积极的指导意义。     

海洋混合层结构对表面声道中声传播特性的影响分析

利用WOA05气候态数据集和北黄海调查数据,应用BELLHOP高斯束射线模型分析了我国近海及西太平洋典型海区的混合层结构对表面声道中声传播特性的影响,结果表明:我国近海的混合层结构有显著的区域性和季节性变化;深海中主要表现为混合层深度变化,这种变化直接影响表面声道的空间分布,声波在混合层中的表面声道中传播与在混合层外的影区中传播产生的能量场差异较大;浅海中混合层深度与声速梯度的空间变化都很明显,声速梯度的增大和混合层的加深都能使更多声线以反转的形式传播,使表面声道声场增强。两组海上实验数据表明,在真实海洋中混合层可在短时间内出现生消变化或在局部海域出现非均匀分布。在浅海温跃层环境下,海-气边界特定的物理过程能够使混合层发生间歇性的变化,当表面声道出现时近表层声场明显增强。     

Acoustic telemetry--An overview

Acoustic telemetry from underwater submersibles and sensors has been pursued ever since it was recognized that the ocean could support signal transmission. While it has been evident that some form of communication is possible, the ocean has proved to be a distressingly difficult medium in which to achieve high data rates. High data rate transmission requires a wide bandwidth which is severely constrained in the ocean because of the absorption of high-frequency energy. Moreover, the ocean is a very reverberant environment with both time and frequency spreading of signals; this further limits data transmission rates. The net effect of the bandwidth and reverberation constraints has led to either acoustic telemetry systems with low data rates or to the use of tethered systems. Over the years, various forms of acoustic communication systems have been developed. These have included direct AM and SSB for underwater telephones, FM for sensor data, FSK and DPSK for digital data, and parametric sonars for narrow-beam systems. As offshore operations have increased, several other systems have been proposed and/or built to respond to particular needs. In this paper, we review the underwater channel and the limitations that it imposes upon acoustic telemetry systems. We then survey some of the systems that have been built (excluding military systems) and indicate how they use various communication system principles to overcome these limitations.     

声诱饵反鱼雷水声对抗发展现状及趋势

鱼雷作为水下最重要的进攻武器之一,可针对水下及水面目标发起非对称隐蔽攻击。随着近几十年电子技术的发展,鱼雷更加智能化,杀伤力更大。因此反鱼雷任务成为现代海战中一项重要的课题。主要介绍了国外近年装备的鱼雷型号,并对国外鱼雷对抗用声诱饵作了介绍,最后对声诱饵的未来发展趋势做了展望,为今后我国发展声诱饵技术提供参考。     

Acoustic Doppler current meter

A current meter designed to measure velocity profiles in the water column above the bed is described. The solution proposed is a coherent backscatter Doppler sonar system using a single transducer. A range-velocity product of 20 m²/s can be achieved by combining state of the art sonar techniques with new processing methods and careful, highly flexible design. Large range-velocity products and very short range resolution together with the possibility of acquiring sensible results without averaging over long time periods are features of this current meter     

Precise Multibeam Acoustic Bathymetry

The maximum error in ocean depth measurement as specified by the International Hydrographic Organization is 1% for depth greater than 30m. Current acoustic multibeam bathymetric systems used for depth measurement are subject to errors from various sources which may significantly exceed this limit. The lack of sound speed profiles may be one significant source of error. Because of the limited ability of sound speed profile measurement, depth values are usually estimated using an assumed profile. If actual sound speed profiles are known, depth estimate errors can be corrected using ray-tracing methods. For depth measurements, the calculation of the location at which a sound pulse impinges on the sea bottom varies with the variation of the sound speed profile. We demonstrate that this location is almost unchanged for a family of sound speed profiles with the same surface value and the same area under them. Based on this observation, we can construct a simple constant-gradient equivalent sound speed profile to correct errors. Compared with ray-tracing methods, the equivalent sound speed profile method is more efficient. If a vertical depth is known (or independently measured), then depth correction for a multibeam system can be accomplished without knowledge of the actual sound speed profile. This leads to a new type of precise acoustic multibeam bathymetric system.     

Acoustic correlation current profiler

An acoustic correlation current profiler (ACCP) system is being developed to obtain vertical profiles of current velocities to ranges of approximately 1500 m. A single transmitter and a spatial array of eight receivers arranged in a novel geometry are employed to measure water mass displacement from receiver array cross-correlation functions. Test data from a shallow water ACCP operating at 76.8 kHz are presented and compared to model predictions as well as to velocity profiles obtained simultaneously during the tests from an adjacent acoustic Doppler current profiler. Additionally, predicted performance data for a lower frequency deep-water unit are presented     

Precise Multibeam Acoustic Bathymetry

The maximum error in ocean depth measurement as specified by the International Hydrographic Organization is 1% for depth greater than 30m. Current acoustic multibeam bathymetric systems used for depth measurement are subject to errors from various sources which may significantly exceed this limit. The lack of sound speed profiles may be one significant source of error. Because of the limited ability of sound speed profile measurement, depth values are usually estimated using an assumed profile. If actual sound speed profiles are known, depth estimate errors can be corrected using ray-tracing methods. For depth measurements, the calculation of the location at which a sound pulse impinges on the sea bottom varies with the variation of the sound speed profile. We demonstrate that this location is almost unchanged for a family of sound speed profiles with the same surface value and the same area under them. Based on this observation, we can construct a simple constant-gradient equivalent sound speed profile to correct errors. Compared with ray-tracing methods, the equivalent sound speed profile method is more efficient. If a vertical depth is known (or independently measured), then depth correction for a multibeam system can be accomplished without knowledge of the actual sound speed profile. This leads to a new type of precise acoustic multibeam bathymetric system.     

Kraken海洋声学模型及其声传播与衰减的数值试验

针对射线、简正波、PE、FFP等传播模型的算法原理及其适用的海洋环境,建立了以Kraken声学模型计算软件为基础的海洋声场数值预报系统.应用该预报系统对4组典型的海洋声场进行了数值试验,结果表明:在相同的海面和海底边界条件下,声场分布是由声速剖面和声源位置决定的.在负梯度声场中,所有声线都折向海底,在极限声线外产生阴影区.声源位于声道轴附近的温跃层中会产生波导传播.用射线理论解释了上述现象的成因,指出了其实际应用价值.     

Accuracy assessment of GPS/Acoustic positioning using a Seafloor Acoustic Transponder System

The accuracy of GPS/Acoustic positioning is crucial for monitoring seafloor crustal deformation. However, the slant range residual is currently the only indicator used to evaluate the precision of positioning seafloor transponders. This study employs a unique Seafloor Acoustic Transponder System (SATS) to evaluate the accuracy of GPS/Acoustic seafloor positioning. The SATS has three transponders and an attitude sensor in a single unit, which provides true lengths of transponder baselines and true attitude of the SATS to ensure assessment reliability and validity. The proposed approach was tested through a GPS/Acoustic experiment, in which an off-the-shelf acoustic system was used to collect range measurements. Using GPS/Acoustic geodetic observations, the positions of three transponders on the SATS were estimated by an optimization technique combined with ray-tracing calculations. The accuracy of the GPS/Acoustic seafloor positioning is assessed by comparing the true baselines and attitude with the results derived from the position estimates of the three transponders. A sensitivity analysis is conducted to investigate the robustness of the GPS/Acoustic positioning results to changes of sound speed. Experimental results demonstrate that the use of the SATS can help to assess the validity of the GPS and acoustic travel time measurements in the GPS/Acoustic seafloor positioning.     

Acoustic classification of abyssopelagic animals

The unique environment of the abyssal plains allows many simplifying assumptions, facilitating the acoustic classification of an animal into one of two groups. The most important assumptions are based on low population densities and available target strength histograms and swim rate histograms. The likelihood ratio is formed from this information and accepted signal processing theory. The likelihood function, a three-dimensional integral, is analytically simplified to one dimension and then solved numerically. A simulation based on this solution and measured data demonstrates that classification using the likelihood ratio approach is accurate, e.g. the sensitivity is ⩾0.8. Although the measured data come from two abyssopelagic genera, the methods presented are more generally applicable. Simulations based on hypothetical animal populations show that under certain conditions, a near perfect classification can be made, e.g. sensitivity and specificity greater than 0.969