深海季节性环境变化对半会聚区尺度水面声定位影响分析

针对深海声定位受海洋环境变化影响明显、需考虑测量系统的环境适应性和宽容性设计问题,提出一种评估海水环境变化对定位性能影响的仿真分析方法,将声场计算、误差传播与交会解算联合建模,以西太平洋中纬度海域夏季和冬季环境为代表性场景讨论了季节性环境变化对定位性能的影响方式和影响程度。仿真结果表明,当接收器位于海洋近表层时,在夏季和冬季呈现出两种不同的声信道样式,夏季季节性温跃层影响下的定位精度较差,冬季表面波导影响下的定位精度相对较好,两者均方根误差(RMSE)相差超过50 m;当接收器位于海洋中上层时,直达波有效作用范围的季节性变化引起定位性能差异,冬季定位精度优于夏季,两者RMSE相差15～20 m;当接收器位于海洋近底层时,利用可靠声路径定位精度较高,定位性能季节性变化不明显。研究认为,海水的季节性环境变化能够改变半会聚区尺度水面声定位的声信道特性以及到达声信息、误差传播、交会求解等测量因素,进而对接收深度位于海洋上层的声定位性能产生明显影响。     

浅海声传播和混响的选频衰减

在强负跃层浅海的爆炸声实验中,发现当声源和接收器都位于跃层之上时,平均混响强度和某一航向的声传播损失在频率1000-2000Hz之间出现强烈的异常衰减现象,而且很有意思的是发射和接收均无指向性的平均混响强度的异常衰减与该航向声传播损失的异常衰减具有中心频率相同、带宽一致、附加衰减值相近的窄带共振或选频衰减特权.显然,这一异常衰减现象无法用各向异性的机理(内波、海面或海底的有规律起伏等)来解释.根据本文实验所得的传播损失和混响强度的深度结构以及一些间接的证据,我们认为这一选频附加衰减是由分散活动干跃居上部的有鳔鱼(极可能是鱼)所引起的.     

台风“天秤”对两种深海声道下声传播的影响

将Argo浮标资料与卫星遥感再分析数据相结合,调用基于抛物方程算法的RAM(Range-dependent Acoustic Model)模型,研究了2012年第14号台风“天秤”对不完整深海声道(3 000 m)和完整深海声道(5 500 m)两种水深条件下声传播特性的影响。结果显示:台风对海水的影响局限于表层水体,具体为混合层加厚,混合层内温度梯度接近于零,声速在混合层内正梯度分布;混合层下方一定深度的水体增温,相应的声速也增大。声源在混合层内时,主要对海表层的声传播产生影响,两种水深条件下均出现表面波导声传播模式以及泄漏模式。声源在混合层以下时,不完整深海声道条件下台风使得会聚区向着声源方向靠近;完整深海声道条件下台风对会聚区的位置影响不明显,但声波的翻转深度增加近500 m。     

珠江口低盐透镜现象的声传播特性分析

低盐透镜现象是珠江口陆架海域常见的一种中尺度现象,它的出现会影响水下声传播环境。利用南海北部陆架区的CTD资料分析了低盐透镜的结构特征,基于简正波和射线模型,建立二维波导环境,设置不同声源条件,对低盐透镜环境的声传播特性进行了研究。结果表明:低盐透镜会在海水上层形成声道,距离15 km处其传播损失较没有低盐透镜的情况小约15 dB。虽然低盐透镜声道厚度通常较小,但是较大的盐度梯度可以保证声道对声能的有效传播。当频率高于截止频率的声源置于低盐透镜内,声道效应有助于声音的远距离传播。     

Frequency-selective attenuation of sound propagation and reverberation in shallow water

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High-frequency forward scattering from the sea surface: thecharacteristic scales of time and angle spreading

Forward scattering from the sea surface is discussed in the contest of a forward bounce path, or channel, through which high-frequency sound energy is transmitted. Such a channel might be used in an underwater communication or imaging task. Both time and angle spreading are inherent to the process of forward scattering by a roughened sea surface. Spreading in each domain relates, via Fourier transform, to a conjugate or coherence separation variable, e.g., angle spreading and spatial coherence. The measurement and modeling of time and angle spreading are discussed, with the modeling incorporating the bistatic cross section of the sea surface. A characteristic scale for each spread variable is defined: L for the time spread and σ_&thetas;h and σ_&thetas;v for the horizontal and vertical angular spread, respectively. Simplified expressions for these characteristic scales as a function of array acquisition geometry and sea surface conditions are also obtained. Data from two field experiments are discussed, one conducted in shallow waters of 30-m depth, and one conducted in deep, pelagic waters of 4000-m depth. Both experiments utilized frequencies ⩾20 kHz. The role of bubbles in forward scattering is illustrated using measurements from the deep-water experiment. It was demonstrated that bubbles can attenuate the forward-scattered signal, but otherwise have little effect on L and σ_&thetas;h,v until their concentrations approach those necessary to nearly extinguish the signal scattered from the air/sea interface     

Specific features of reverberation in the Black-Sea underwater sound channel

We consider the results of instrumental investigations of specific features of reverberation in the Black Sea and obtain qualitative dependences of the duration of volume reverberation on the parameters of the Black-Sea underwater sound channel, (width, drop of the sound velocity, and dimensions of the inhomogeneities of stratification). We also analyse the behaviour of the intensity of surface reverberation in the far-field zone of acoustic illumination and the influence of bottom reverberation on the detection of underwater objects. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

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。     

Boundary characterization experiment series overview

Ocean acoustic propagation and reverberation in continental shelf regions is often controlled by the seabed and sea surface boundaries. A series of three multi-national and multi-disciplinary experiments was conducted between 2000-2002 to identify and measure key ocean boundary characteristics. The frequency range of interest was nominally 500-5000 Hz with the main focus on the seabed, which is generally considered as the boundary of greatest importance and least understood. Two of the experiments were conducted in the Mediterranean in the Strait of Sicily and one experiment in the North Atlantic with sites on the outer New Jersey Shelf (STRATAFORM area) and on the Scotian Shelf. Measurements included seabed reflection, seabed, surface, and biologic scattering, propagation, reverberation, and ambient noise along with supporting oceanographic, geologic, and geophysical data. This paper is primarily intended to provide an overview of the experiments and the strategies that linked the various measurements together, with detailed experiment results contained in various papers in this volume and other sources.     

基于遥感数据和表层声速的全海深声速剖面反演

海洋声速剖面严重影响着水下声传播特性,近实时地获取声速剖面对水下声通信、水下定位、鱼群探测等都有重要意义。单经验正交函数回归（single Empirical Orthogonal Function regression,sEOF-r）方法通过建立声速剖面的经验正交系数与海面遥感数据之间的线性回归关系来反演声速剖面。但是,海洋是一个复杂的动力系统,声速与海面遥感数据并不是简单的线性关系,因此,本文基于Argo历史网格数据,通过自组织映射（Self-Organizing Map,SOM）生成海平面高度异常（Sea Level Anomaly,SLA）、海表面温度（Sea Surface Temperature,SST）等海表遥感数据以及表层声速仪测量的表层声速与声速剖面异常之间的非线性映射;然后利用近实时的海表遥感数据和表层声速反演三维海洋声速场。声速剖面反演的结果表明,在多源信息融合的优势下,本文方法的反演性能最稳定且精度最高,声速剖面的平均反演精度比经典sEOF-r方法提高约2 m/s,比未考虑表层声速的经典SOM方法提高约1 m/s。     

Imaging of long‐range reverberation from ocean basin topography

A technique is currently under development a the Naval Research Laboratory for imaging of backscatterec acoustic returns from ocean basin topography. The method is straightforward. An explosive sound source is detonated near the center of an ocean basin and the round‐trip travel time from source to reflectors and return is measured. Distance to back‐scattering topography is assumed to be proportional to round‐trip time, with a proportionality constant equal to half the sound speed. A multielement receiving array is used to determine the azimuthal directions to topographic features. Reverberation data are output to an imaging system to study the spatial distribution of sea bottom reverberation. The images are in the form of two‐dimensional maps of backscattered acoustic energy. Typical maps are larger than 2,000 km x 2,000 km (or area coverage greater than 4 x 10⁶ km²). After correction of maps from individual shot detonations for range‐dependent propagation losses, we average ("integrate") maps together on a pixel by pixel basis for a clear picture of major basin reverberators.     

Modeling of volume reverberation in the ray approximation

We propose a numerical model for the evaluation of the three-dimensional scattering of sound in the sea. The model is based on the construction of ray patterns both for the primary and secondary (scattered) radiation. The intensity of secondary radiation is expressed via the coefficient of backward volume scattering interpreted as the fraction of backward-scattered acoustic energy per unit length of the primary ray. It is shown that, in the first approximation, it suffices to consider the secondary rays repeating the paths of the primary rays in the opposite direction. The attenuation of the intensity of sound along the paths of the primary and secondary rays is taken into account. The results of numerical analysis of the reverberation signal as a function of time are presented for various conditions (different depths of immersion of the antenna and widths of the directional diagram and the presence of sound-scattering layers). The proposed approach can be used for the purposes of modeling of the surface and bottom reverberation and for the solution of the inverse problems of underwater acoustics. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 50–58, September–October, 2007.     

一种新的声速剖面结构参数化方法

在Munk模型和GDEM模型的基础上,提出了一种新的声速剖面结构参数化模型,即分层声速剖面模型(LSSPM).模型用含9个参数的四层分段函数分别描述混合层、主跃层、深海声道层和深海等温层的声速结构,形式简明、直观.数值实验结果表明,LSSPM模型对声速剖面的拟合可达到较高的精度,且对于中国周边的深海和浅海区域有较好的适...     

An oceanic reverberation model

A simple model of the surface, volume, and bottom reverberation received by a moving platform as a function of time following the tranmission of a narrow-band pulsed signal is described. Both the time-varying power level and the underlying power spectrum are predicted. The model includes the effects of platform motion, transmit signal windowing, transmit and receive beam patterns, and the environment (surface, volume, and bottom backscattering strengths, the scatterer velocity distributions for surface waves and current layers, and sound absorption). An isospeed sound speed profile is assumed and reflections at the surface and bottom boundaries are not permitted. Also described is a matched filter-envelope detector receiver model for post processing of the reverberation spectra.     

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。     

Analysis of shallow-water experimental acoustic data including acomparison with a broad-band normal-mode-propagation model

Channel temporal variability, resulting from fluctuations in oceanographic parameters, is an important issue for reliable communications in shallow-water-long-range acoustic propagation. As part of an acoustic model validation exercise, audio-band acoustic data and oceanographic data were collected from shallow waters off the West Coast of Scotland. These data have been analyzed for temporal effects. The average impulse response for this channel has been compared with simulations using a fast broad-band normal-mode propagation model. In this paper, we also introduce a novel technique for estimating and removing the bistatic reverberation contribution from the data. As propagation models do not necessarily account for reverberation, it has to be extracted from the signals when comparing measured and modeled transmission loss     

Shallow water reverberation: normal-mode model predictions comparedwith bistatic towed-array measurements

A normal-mode model for calculating reverberation in shallow water is presented. Some illustrative calculations are given for the bistatic case and for vertical and horizontal line-array receivers. Emphasis is on comparison with measurements of bistatic reverberation obtained at a shallow-water area in the Mediterranean. The data are from explosive sources received by a towed array, analyzed in one-tenth-decade frequency bands at subkilohertz frequencies. Model calculations for a flat-bottomed environment indicate a strong dependence on propagation conditions and a weak dependence on beam steering direction. Preliminary comparisons give quite good agreement between measured reverberation and model predictions, but point to the need for extending modeling efforts to handle range-dependent environments     

琉球群岛附近海域声场分析

利用美国海军的GDEM(generalized digital environm ental model)数据对琉球群岛附近海域声场进行了研究,分析了该海域声速最小值分布及其对应深度的分布规律;研究了横跨和穿越宫古水道两个断面上上述声场特征的变化,结果表明杭州湾以北的沿岸约30m地形等深线内,冬、春、秋季声速最小值出现在海面,并且有较为稳定的表面声道;夏季闽浙沿岸约30m地形等深线内,声速最小值出现在海面.奄美群岛、冲绳岛东侧130km范围内有很强的海水混合,上升流很明显,导致声速最小值出现的深度在冬夏比在春秋的深400m.     

加州海狮水下声信号的分析

国外对加州海狮水下声进行了不少研究,但尚未取得一致结论。我们对北京动物园中的加州海狮(Zalophus californianus) “东东”和“玲玲”的水下声信号进行了测试和分析。发现它们在水下发出许多种声信号。在缓慢的自由游泳状态发出幅度较低、没有明显规律的脉冲,而当快游接近池壁或跳出水面之前和入水之时,则发出上升时间短、幅度很大的脉冲列。“东东”三岁半,好动,发声极多,其脉冲声信号较易测到。     

浅海均匀层远程混响的垂直相干性

混响是主动声纳在浅海环境中的一种干扰,有关其空间相关特性,Urick和Lund发表了两篇实验性报告[7].本文根据浅海平均声场角度谱分析法[3],从理论上计算了浅海均匀层远程混响垂直相关特性与界面反射、散射等环境参数之间的关系,及其随距离、水听器间隔的变化,供声纳设计或在浅海环境中研究低频、小掠角的散射特性时参考.