一种基于声速剖面展开的内波监测新方法

声速剖面时空分布的获取是利用声学方法监测内波的核心问题。在反演算法中,声速剖面通常是采用展开的方式用若干个参数来表示的。这就导致了有时很难从反演结果中直接获得内波的相关信息。本文的目标是找到一种通过展开系数直接获取内波特性的方法。通过推导内波水动力方程,可以从较少的声速剖面样本中提取出水动力简正模态（Hydrodynamic Normal Modes,HNMs）作为声速剖面展开的正交基。较之广泛采用的正交经验函数（Empirical Orthogonal Functions, EOFs）,HNMs直接与内波活动相关,具有更明确的物理含义。然后,基于HNMs对声速剖面的时间序列进行展开,获得展开系数。最后,从前两阶展开系数的时间导数中可以获取内波活动的信息。将方法应用于受内波影响而具有明显时空扰动的南海北陆架区温度链数据,结果表明：只用前两节模态就可以在较好的精度范围内重构声速剖面。前两阶系数的时间导数具有独特的双震荡结构可以用于探测内孤立波。从展开系数也可以获得幅度以及波长信息。理论推导和实验分析证明了本文方法在内波监测中的有效性。HNMs方法使用便利且对样本的依赖性较小,可以在内波活跃海域作为EOFs的有效补充用于声速剖面的展开。     

声速剖面EOF重构的实测数据采样深度研究

经验正交函数（experiential orthogonal functions,EOF）是重构声速剖面（sound speed profile,SSP）的一种有效方法,利用部分实测数据结合历史剖面资料可以重构当前位置的声速剖面。针对实测数据的采样深度难以确定这一问题,本文介绍了一种基于历史声速剖面资料的实测数据采样深度选取方法,根据EOF空间函数的方差贡献率确定数据量,进而采用EOF算法重构全海深声速剖面。实验结果表明：采用该方法得到的数据重构的声速剖面与实测声速剖面具有较好的一致性,基于常梯度声线跟踪法得到的水深数据能够满足0.25%倍水深限差,有效波束比达到了100%,为实际测量作业中声剖数据的采样深度提供了参考。     

基于正交匹配追踪的声层析方法

声速剖面的变化会对声传播产生较大的影响,经验正交函数模型经常用来实现对声速剖面数据的简化描述。然而在内波、湍流等海水不均匀性存在时,这种正则化操作会造成声速重构精度的大幅降低。本文利用字典学习生成声速剖面的非正交原子,在稀疏编码时采用正交匹配追踪（OMP,Orthogonal Matching Pursuit）算法,更新字典则使用KSVD （Kernel Singular Value Decomposition）的字典更新算法。由于字典学习不需要强制使用正交条件,对于训练数据更加灵活,从而可以使用少数的原子组合达到更高的重构精度。利用一次浅海声学实验多次测量的声速剖面研究了海水声速剖面的经验正交函数表示和字典学习,研究表明：相比于正交函数表示,学习字典可以利用少数原子（甚至一个原子）更好的解释声速剖面扰动。字典学习可以提高声速剖面的稀疏性,从而提高声速剖面的反演精度。     

Remote sensing of ocean sound speed profiles by a perceptron neuralnetwork

A method is developed to estimate ocean sound speed profiles through synthesis of remotely measured environmental data and historical statistics of sound speed obtained at a remotely sensed location. Sound speed profiles are represented by an expansion of empirical orthogonal functions (EOF) of the historical sound speed variation, while the remotely sensed environmental data provide real-time information to determine the expansion coefficients. Environmental inputs are limited to sea surface temperature available from satellite infrared sensors, acoustic time-of-flight and ocean bottom temperature measurable from bottom mounted acoustic and thermal transducers. A multilayer perceptron neural network is implemented to learn the functional transformation from the measured environmental input to the desired EOF coefficient output on a set of representative sound speed profiles. Sea surface temperature, time-of-year, and time-of-flight from the acoustic multipath that maximally samples the vertical sound speed are found to be the dominant inputs. The trained network is computationally efficient and produces estimates for untrained environmental inputs with a mean error of 1.1-4.4 m/s     

Underwater Navigation Based on Real-Time Simultaneous Sound Speed Profile Correction

Precise sound speed profile (SSP) information is critical when using sonar for underwater terrain navigation. Nevertheless, acquiring SSP information in real-time is difficult, especially in underwater navigation environment. To account for this problem, this paper presents an underwater navigation method that applies real-time SSP correction to the terrain measurements. The method uses a probe to measure the surface sound speed simultaneously. Meanwhile, redundancy of topographic measurement data is exploited to derive the equivalent SSP information. The acquired equivalent SSP is updated continuously with particle filter algorithm. The terrain measurements can be corrected in real-time with the equivalent SSP to improve the performance of underwater terrain navigation. By removing the impact of inaccurate SSP from the terrain measurements, the proposed method can achieve precise and robust underwater navigation result without using an underway-profiling instrument. Simulated results confirm the good performance of the proposed method.     

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。     

Rapid environmental assessment in the South China Sea: Improved inversion of sound speed profile using remote sensing data

Complex perturbations in the profile and the sparsity of samples often limit the validity of rapid environmental assessment (REA) in the South China Sea (SCS). In this paper, the remote sensing data were used to estimate sound speed profile (SSP) with the self-organizing map (SOM) method in the SCS. First, the consistency of the empirical orthogonal functions was examined by using k-means clustering. The clustering results indicated that SSPs in the SCS have a similar perturbation nature, which means the inverted grid could be expanded to the entire SCS to deal with the problem of sparsity of the samples without statistical improbability. Second, a machine learning method was proposed that took advantage of the topological structure of SOM to significantly improve their accuracy. Validation revealed promising results, with a mean reconstruction error of 1.26 m/s, which is 1.16 m/s smaller than the traditional single empirical orthogonal function regression (sEOF-r) method. By violating the constraints of linear inversion, the topological structure of the SOM method showed a smaller error and better robustness in the SSP estimation. The improvements to enhance the accuracy and robustness of REA in the SCS were offered. These results suggested a potential utilization of REA in the SCS based on satellite data and provided a new approach for SSP estimation derived from sea surface data.     

Basis functions for shallow-water temperature profiles based on the internal-wave eigenmodes

The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function(EOF)coefficients. However, when the experimental area is poorly known or highly variable, the adaptability of the EOFs will be significantly reduced. In this study, a new set of basis functions, generated by combining the internal-wave eigenmodes with the average temperature gradient, is developed for characterizing the temperature perturbations. Temperature profiles recorded by a thermisto...     

表层声速误差对多波束测深数据的影响分析

针对多波束水深测量中未明确定义表层声速限差范围,导致在数据采集过程中无法实时监控表层声速误差的问题,结合多波束数据采集与归算流程,分析并推导了 SSP误差影响下的波束指向角与点位归算误差模型.结合数值计算,研究了不同水深下测深误差随SSP之间的变化规律与量级大小,从而针对SSP限差范围提出合理化建议,对提高数据质量具有...     

Multistatic localization error due to receiver positioning errors

This paper is a summary of a study of the effect of receiver position errors on the target localization accuracy of a multistatic sonar. The multistatic active system under examination consists of one or more transmitters and receivers, and the target is localized in the horizontal plane by means of echoes from the transmissions. Two-dimensional propagation of sound, with a constant sound speed, is assumed throughout. A simple analytic approach, implemented and illustrated numerically, is derived for calculating the sensitivity to receiver position error over a specified area. For many of the examples considered, there are considerable regions where target localization errors can be unacceptably large even for highly accurate receiver positions     

Sound sources and levels in the ocean

The standard definitions found in the American National Standards on Acoustics are applied to common sound sources used in both underwater acoustics research and naval sonar system operation. Recommended metrics are quantified for both continuous and transient sources of sound. Standard definitions are reviewed with theoretical sound source models. Requisite metrics are derived and applied to examples of energy sources of sound, such as transients from a small omnidirectional explosive, an air gun, a light bulb, and a dolphin click. A generic quantitative model of surface ship sonar system emissions is developed. Active sonar transmissions are analyzed with the requisite quantitative metrics required to characterize these emissions. These results should be useful in environmental assessments, biological experiments, and the sonar system design.     

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...     

A Tactical Approach to Environmental Uncertainty and Sensitivity

The issues of acoustic sensitivity to environmental parameters and the uncertainty in performance prediction due to lack of accurate environmental inputs are addressed. Special emphasis is given to the current state of affairs and to the importance of communicating in a simple, robust means the uncertainty to the sonar operator. A multistaged approach to estimating sensitivity, computing acoustic propagation uncertainty due to environmental variability is presented. A heuristic approach to estimating the most sensitive environmental parameters is developed. A measurements-based statistical approach is applied to environmental data taken in the Mediterranean Sea to estimate performance uncertainty due to sound speed and geoacoustics uncertainty     

Study of the low-frequency variability of the atmospheric general circulation with the use of time-dependent empirical orthogonal functions

The theory of both time-and space-dependent empirical orthogonal functions (EOFs) is outlined from a common point of view as a discrete version of the Karhunen-Loeve expansion. EOF techniques are used to process the results of a 1300-day-long numerical experiment in the mode of perpetual January with a daily step. As a result, the component determined by internal hydrothermodynamic processes was isolated from the general variability of the atmospheric circulation. To isolate intraseasonal variability (a winter season), the principal components of the 500-hPa height field were processed with a filter close to a π-shaped filter isolating the frequency band 0.1–0.01 day^?1. The spatial principal components were analyzed via the method of time-dependent EOFs. The spectral characteristics obtained can characterize the intraseasonal low-frequency variability and agree partially with empirical data.     

改进型经验正交函数海洋声速剖面预报方法

鉴于深海温跃层以下往往声速值缺乏,声速剖面不完整的原因,提出一种声速剖面的预报方法:在传统经验正交函数预报法基础上,首先改进协方差矩阵的求解方法,将原始数据的空间信息和时间信息有效地融合到协方差矩阵中,通过由大量实测数据统计得出的时间函数的经验公式,得到合成剖面,将二者结合,把不完整剖面垂直向下延拓到海底,较为有效地解决了传统方法求解协方差矩阵和时间函数较粗糙的问题,给出了完整的海洋声速剖面的准确预报.实测数据检验结果表明,改进方法的预报精度比传统方法有了很大提高.     

Accuracy of the spatial representation of the seafloor with bathymetric sidescan sonars

When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350, U.S.A.     

多波束声纳计量测试系统设计

为满足多波束声纳量值溯源与传递需求,设计多波束声纳关键参数的计量测试系统。基于大比尺原型深水港池和多维运行控制机构,通过水下横向测距代替垂向测深的方式对多波束声纳进行了测深准确度与有效条带宽度的计量测试。阐述了测试系统的主要组成和测试方法,给出了本测试系统测深结果的扩展不确定度。参考标准值与示值(或标称值)比对结果表明,被检多波束声纳测深示值误差小于0.2%,条带宽度误差小于7%。为规范水下声纳设备技术指标校准,指导多波束声纳计量标准建设提供参考。     

Acoustic backscattering from a sandy seabed

Acoustic backscattering from a sandy seabed was measured at a frequency of 5.5 kHz at a wide range of grazing angles. The measurement system used was the University of Miami's sonar tower, consisting of an omni-directional broadband source and two 16-channel hydrophone receiver arrays. A volume scattering model, which combines a fluid model with reflection/transmission coefficients derived from the Biot theory, is used. This model allows energy penetration into the bottom, calculations of the volume scattering at all grazing angles, and the frequency dependence of the sound speed in the water-saturated sediment. In the model, rather than assume sound-speed correlation length in sedimentary volume, core data were used to assimilate a 3-D fluctuation spectrum of the density. The numerical results showed excellent agreement with the measurement at lower grazing angles. We concluded that the interface roughness scattering was dominant at lower grazing angles, while the volume scattering is dominant at higher grazing angles at the sandy site. The border of the dominance of the interface and volume scattering was the so-called critical angle at this frequency. The frequency dependence of sound speeds is also discussed.     

黄海冷水团声层析监测数值模拟

海洋冷水团是海洋学家关注多年的问题 ,其监测方法亟待解决。本文将简正波波数层析法用于冷水团监测 ,并对简正波波数层析用于反演黄海冷水团声速剖面进行了数值模拟。数值模拟结果表明 ,简正波波数层析可以用于反演平均声速剖面 ,特别在监测与距离有关海洋环境的声速结构方面大有潜力。     

多波束测深边缘波束误差的综合校正

边缘波束误差是影响多波束测深数据精度的主要因素,数据精度影响其可信度和使用范围,也是进行相关研究的基础.多波束勘测系统声呐参数的精确校正、勘测区声场模型的建立以及实时勘测海洋噪声的合理剔除是影响边缘波束数据质量的关键因素,严重时甚至导致勘测数据出现沿测线方向的条带状假地形或地形位置偏移.上述因素对多波束勘测数据的影响是一个综合作用的过程,靠单一的校正或编辑方法很难提高采集数据的精度.以多波束勘测原理和声学理论为指导,以多波束实测数据为研究基础和分析对象,运用GIS面向对象方法,全面分析造成多波束勘测大误差边缘波束的原因,并探寻改善已勘测多波束大误差数据、提高数据精度的综合处理方法,最终以可视化的方式实现人机交互处理.该项研究成果已初步应用于海洋项目总图编绘工作,并取得了预期效果.