基于射线模型的浅海水声传播仿真研究
海水和沉积物中声传播损失的仿真分析
海水 沉积 作用形 成 的表
层松 散 的沉积物 层 和该 层下 已凝结 的坚 硬 岩石
无 关 的水 声 环 境 以及 其 处 理 低 频 声 信 号 的 高 效
性， 因此 ， 利用波数积分法＿计算低频声传播损失 １ ］
是合理的 。
图 １ 分 层 海 底 模 型
所构 成 的基 底 组 成 ， 如
关系 ， 定量 的研 究 声 波 在 海 水 和 沉 积 物 中 接 收 时 的传 播 损失 差 异 。 由于波 数 积 分 法适 用 于与 距 离
达式。待定系数通过同时满足所有界面上 的边界条
件而求得 ， 总声场则通过计算积分表达式来确定 。
在 计 算 浅 海 声 场 时 ， 以认为 海底是 由 可
摘
要
文章建立 了水一 沉积物一海底半空间 的分层海底模 型， 通过 仿真计算 ， 比较 了声 波在海水 和沉积 物中接收 时
的传播 损失差异 。结果表 明， 在高声速海底 的条件下 ， 声波在沉积物 中传 播且频 率较低 时， 传播 损失较低 ， 即低频声 波更易
于在沉积物 中传播 。 关键词 分层海底 ； 沉积物 ； 传播损失 声
总 第 ２ ４期 ０
舰 船 电 子 工 程
Ｓ ｉ ｅ ｔｏ ｉ ｇ ｎ ｅ ｉ ｇ ｈ ｐ Ｅｌ ｃ ｒ ｎｃ Ｅｎ ｉ ｅ ｒｎ
Ｖｏ ＿ １ Ｎｏ ６ ｌ３ ．
１ ８３
２ １ 年第 ６期 ０１
海水 和 沉 积 物 中声 传 播 损 失 的仿 真 分 析
蚌埠市 禹会 区燕山路 １ ５ 号 ４４
０４ ７ ２ 中 图分 类 号
Ｓｉ ｕ ａ ｉ ｎ Ａｎ ｙ ｉ ｎ Ａｃ ｕ ｔｃ Ｔｒ ｎｓ ｉ ｓｏ ｓ ｍ ｌ ｔｏ ａｌ ｓ ｓ ｏ ｏ ｓ ｉ ａ ｍ ｓ ｉ ｎ Ｌｏ ｓ
海底三维散射模型仿真研究
（ ９ １ ３ ８ ８部 队
５ ２ ４ ０ ２ ２ ）
摘
要
海底声 散射强度是 浅海 混响预报 的一个重要物理量 。采用 Ｊ ａ ｃ ｋ ｓ ｏ ｎ 复合粗糙度模型研 究了非 均匀海底界面 的声 散射问题 ， 对
模 型进行 了理论 推导和仿真计算 ， 利用 已发表 的海底散射强度实测数据与模型仿真结果进行对照 ， 验证了模型的正确性 ， 并就海底沉积物类 型和海底声学特性参数 对海底反 向散射强度 的影 响进行 了分析 。 关键词 海底散 射；界面散射 ；体积散射 ； Ｊ ａ ｃ ｋ ｓ ｏ ｎ模型
研究 。Ｄ ａ ｌ ｅ Ｄ ． Ｅ ｌ ｌ ｉ ｓ 等人 ＿ ２ ］ 利用 Ｋｉ ｒ ｃ ｈ ｈ ｏ ｆ ｆ 近似理论 得到了
一
个三维散 射 函数 ， 并 将 此应 用 于收 发分 置 混 响的 计算 ；
海洋声场建模与仿真技术研究
海洋声场建模与仿真技术研究一、引言海洋，占据着地球表面的约 71%，是一个充满神秘和未知的领域。
在海洋研究中，海洋声场建模与仿真技术作为一种重要的手段，为我们深入了解海洋的声学特性和物理过程提供了有力的支持。
海洋声场是指海洋中声波传播所形成的物理场，它受到海洋环境的多种因素影响，如海洋的深度、温度、盐度、海底地形、海洋生物等。
因此，准确地建模和仿真海洋声场对于海洋声学研究、海洋资源开发、海洋环境保护以及军事应用等领域都具有重要的意义。
二、海洋声场建模的基本原理海洋声场建模的核心是基于声波传播的物理规律。
声波在海洋中的传播可以用波动方程来描述，常见的有亥姆霍兹方程和抛物方程。
亥姆霍兹方程适用于描述小范围、高频的声波传播，而抛物方程则更适合处理大范围、低频的情况。
在建模过程中，需要考虑海洋介质的物理特性，如声速分布。
声速在海洋中并非均匀分布，而是受到温度、盐度和压力等因素的影响。
通常通过经验公式或者现场测量来获取声速的分布情况。
另外，海底地形也是影响海洋声场的重要因素。
海底的粗糙度、坡度和地质结构都会对声波的反射、折射和散射产生影响。
三、海洋声场仿真的方法（一）有限元法有限元法是一种将连续的求解域离散为有限个单元的数值方法。
通过对每个单元进行分析，然后将结果组合起来得到整个求解域的近似解。
在海洋声场仿真中，有限元法可以有效地处理复杂的边界条件和介质特性。
（二）边界元法边界元法是基于边界积分方程的数值方法，它只需要对边界进行离散化，从而减少了计算量。
对于具有规则边界的问题，边界元法具有较高的计算效率。
（三）射线理论法射线理论法将声波传播视为射线的传播，通过追踪射线的路径来计算声场。
这种方法在处理长距离传播和高频问题时具有一定的优势，但对于复杂的介质和边界条件适应性较差。
四、海洋声场建模与仿真中的关键技术（一）海洋环境数据的获取与处理准确的海洋环境数据是建模与仿真的基础。
这包括海洋的温度、盐度、深度、海底地形等数据的测量和收集。
_浅海水声多途信道建模与仿真
摘 要: 在进行水声信号恢复和增强、目标探测、跟踪、定位、水声通信等技术的研究过程中, 对海洋信道 的仿
真研究是进行这些水声信号处理 仿真的基础。简要分析了水声信道的传 播特性, 主要针对 水声信道 强烈的多径 效应
这一特点, 研究了浅海水声多途信道的物理模型, 并通过 BELLHOP 射线传播模型实现了声 场环境模 拟以及水声 信道
充分的研究。
1 浅海水声信道特点
由于各种自然条件、地理条件等因素的影响, 水 声信道非常复杂。可以说海洋信道是一个环境噪声 高、信道带宽窄、传播损失大、多途效应严重的时变、 空变的随机信道。 111 海洋环境噪声
海洋环境 噪声 [ 1] 主要 来源于海洋动力 噪声、生 物噪声、交通噪声和工业噪声、地震噪声、冰下噪声,
水声信道带宽 [ 2] 受限的主要原因是海洋中水声 信号的吸收损失。它与水声信号频率密切相关, 信号 频率越高吸 收损失越 大。研究 表明, 声波频率 在 4 kH z左右是远距离传播的最佳频率。此外, 水声换能 器带宽的限制也是原因之一。 113 传播损失
声波在海洋介质中的传播损失 [ 2 ] , 主要有 3个方 面: 扩展损耗 ) ) ) 由于波阵面在传播中的不断扩大, 使得单位时间内单位面积上能量减少; 吸收损耗 ) ) ) 声能在传播过程中不可逆的转换为热能而消耗; 边界 损耗) )) 声波在海洋边界的反射使声能发生 / 泄 漏 0。浅海区域由于泥沙、污物的影响, 水质浑浊, 使 得声散射强度较强, 声信号也易被吸收, 因而传播损 失更为严重。 114 多径效应
建模。通过比较不同深度声源的 声场分布, 以及不同收发条件下的 水声信道 冲激响应, 验证了 水声信道 的多径效应、
稀疏性、传播损失、时变空变以及 随机性等特性。
海水和沉积物中声传播损失的仿真分析
海水和沉积物中声传播损失的仿真分析I. Introduction- Background information on the importance of understanding acoustic propagation loss in seawater and sediments- Research objectivesII. Literature Review- Overview of previous research on acoustic propagation loss in seawater and sediments- Review of relevant theoretical models and simulation approaches - Identification of key factors affecting acoustic propagation loss III. Methodology- Description of simulation approach- Choice of acoustic models- Specification of simulation parametersIV. Results and Analysis- Presentation of simulation results- Analysis of factors affecting acoustic propagation loss- Comparison with previous research to validate resultsV. Conclusion and Future Work- Summary of research findings- Implications for acoustic communication and sensing in underwater environments- Recommendations for future research and development of more accurate modelsNote: The above outline is a guideline and may vary depending onthe specific research topic and objectives.I. IntroductionThe underwater environment poses unique challenges for acoustic communication and sensing due to the complex properties of seawater and sediments. Understanding the properties of such environments is crucial for the design and implementation of effective underwater communication and sensing systems. One of the key parameters that affect the performance of these systems is acoustic propagation loss.Acoustic propagation loss is the reduction in the intensity of a sound wave as it propagates through a medium such as seawater or sediments. This reduction is caused by various factors such as absorption, scattering, and reflection. Accurately modeling the propagation loss is crucial for predicting the range and reliability of acoustic communication and sensing in underwater environments.The objective of this research is to explore the factors that affect acoustic propagation loss in seawater and sediments and to develop accurate simulation models that can predict the propagation loss in various underwater environments.II. Literature ReviewNumerous studies have been conducted on acoustic propagation loss in seawater and sediments. These studies have explored various theoretical models and simulation approaches for predicting the propagation loss. Some commonly used models include the Thorp attenuation model and the Bellhop ray tracingalgorithm.An important factor that affects acoustic propagation loss is the frequency of the acoustic wave. Low-frequency sound waves are more easily absorbed by seawater, while high-frequency waves experience more scattering and reflection. Another important factor is the composition of the sediments, as different types of sediment have varying acoustic properties.III. MethodologyThis research will use a simulation approach to model the acoustic propagation loss in seawater and sediments. The simulation will be based on the Bellhop ray tracing algorithm, which is a widely used algorithm for modeling underwater sound propagation. The simulation parameters will be chosen based on the relevant literature review and will include parameters such as frequency, sediment composition, and depth.IV. Results and AnalysisThe simulation results will be presented and analyzed to explore the factors affecting acoustic propagation loss. The results will be compared with previous research to validate their accuracy. The analysis will identify the most significant factors affecting the propagation loss and their relative importance.V. Conclusion and Future WorkThe research findings will provide insights into the factors thataffect acoustic propagation loss in seawater and sediments. The implications of these findings for acoustic communication and sensing in underwater environments will be discussed. Recommendations for future research will also be provided, including the development of more accurate models that can account for complex environmental conditions.II. Literature ReviewAcoustic propagation loss in underwater environments has been studied extensively over the past few decades. Numerous theoretical models and simulation approaches have been developed to predict the propagation loss in seawater and sediments. In this section, we will review some of the most commonly used models and simulation approaches for studying acoustic propagation loss.A. The Thorp Attenuation ModelOne of the most commonly used models for predicting acoustic propagation loss in seawater is the Thorp attenuation model. This model was developed by Daniel H. C. Thorp in 1968 and is based on the assumption that the absorption of sound in seawater is dominated by the effects of viscosity and thermal conductivity.The Thorp attenuation model takes into account the frequency-dependent absorption coefficient of seawater, which increases significantly with increasing frequency. The model also accounts for the effects of temperature, salinity, and pressure on the acoustic properties of seawater.While the Thorp attenuation model has been widely used forpredicting acoustic propagation loss in seawater, it has some limitations. The model does not account for scattering or reflection, which are significant factors affecting acoustic propagation loss in underwater environments.B. The Bellhop Ray Tracing AlgorithmThe Bellhop ray tracing algorithm is a widely used simulation approach for modeling acoustic propagation loss in underwater environments. The algorithm traces the paths of acoustic waves as they travel through the water, accounting for the effects of reflection, scattering, and refraction.The Bellhop algorithm uses a ray theory approach, which assumes that sound waves travel in straight lines between the source and receiver. While this is an approximation, it has been found to be accurate for modeling sound propagation over short distances.One limitation of the Bellhop algorithm is that it requires detailed information about the environmental parameters, such as water depth, sediment composition, and sound speed. However, this information can be difficult to obtain in some underwater environments.C. Other Models and Simulation ApproachesThere are other models and simulation approaches used for predicting acoustic propagation loss in underwater environments, including parabolic equation and finite element models. These models can account for the effects of complex environmentalconditions, but they also require significant computational resources and detailed environmental data.In addition to these models, there have been numerous experimental studies on acoustic propagation loss in underwater environments. These studies have used various techniques such as towed acoustic sources, bottom-mounted receivers, and acoustic tomography.IV. ConclusionAcoustic propagation loss is a critical parameter for the design and implementation of underwater acoustic communication and sensing systems. The literature review has shown that various theoretical models and simulation approaches have been developed to predict the propagation loss in seawater and sediments. The Thorp attenuation model and the Bellhop ray tracing algorithm are two of the most commonly used approaches.The limitations and advantages of these approaches are important to consider when choosing a simulation approach for a specific underwater environment. It is important to recognize that the environmental conditions can significantly affect the accuracy of the models and simulations. Additional research is needed to develop more accurate models that can account for non-ideal conditions typical of real-world underwater environments.III. Challenges and Future Research DirectionsWhile significant progress has been made in understanding and predicting acoustic propagation loss in underwater environments,there are still many challenges and limitations that need to be addressed in order to improve the accuracy and reliability of acoustic communication and sensing systems.A. Non-Ideal Environmental ConditionsOne of the primary challenges in predicting acoustic propagation loss in underwater environments is the wide variety of non-ideal environmental conditions that can affect the accuracy of the models and simulations. For example, water temperature, salinity, and pressure can all have significant effects on the acoustic properties of seawater, but these factors can be difficult to measure accurately and reliably.Another factor that can affect acoustic propagation loss is the presence of bubbles, which can cause significant scattering and absorption of sound waves. Bubbles can be generated by a variety of sources, including ship propellers, breaking waves, and marine organisms, and their effects on acoustic propagation can be difficult to predict.Sediment composition is another important factor affecting acoustic propagation loss. The type and depth of sediment can significantly affect the way that sound waves are transmitted and reflected in underwater environments, and this can vary widely from location to location.B. Limitations of Simulation ApproachesAnother challenge in predicting acoustic propagation loss is thefact that simulation approaches often have limitations in terms of the accuracy and scope of their predictions. For example, the Bellhop ray tracing algorithm is widely used for modeling sound propagation over short distances, but it may not be accurate for modeling sound propagation over longer distances or in complex environments.Finite element and parabolic equation models can account for more complex environmental factors, but they require significant computational resources and detailed environmental data, which may not always be available.C. Future Research DirectionsTo overcome these challenges and improve the accuracy and reliability of acoustic communication and sensing systems in underwater environments, future research should focus on a number of key areas.Firstly, more accurate and reliable measurements of environmental parameters such as temperature and salinity are needed. This could be achieved through the use of more sophisticated sensing technologies and strategic placement of sensors in underwater environments.Secondly, developing more accurate and reliable models and simulation approaches that can account for the effects of non-ideal environmental conditions is critical to improving the accuracy and reliability of acoustic communication and sensing systems.Thirdly, new technologies and approaches for mitigating the effects of bubble-induced scattering and absorption of sound waves are needed. This could include strategies for reducing the generation of bubbles or using signal processing techniques to filter out the effects of bubbles on acoustic propagation.Finally, more research is needed on the effects of sediment composition and structure on acoustic propagation. This could involve developing better monitoring and measurement techniques for sediment properties and using advanced simulation approaches to model the effects of sediment on acoustic propagation.In summary, while significant progress has been made in understanding and predicting acoustic propagation loss in underwater environments, there are still many challenges and limitations that need to be addressed in order to improve the accuracy and reliability of acoustic communication and sensing systems. Continued research in these areas could pave the way for new and innovative applications of underwater acoustics, including improved underwater communication and sensing for scientific, military, and commercial applications.IV. Applications of Underwater AcousticsThe study of underwater acoustics has a wide range of applications in numerous fields, from scientific research to military operations and commercial use cases. In this section, we will explore some of the major applications of underwater acoustics.A. Scientific ResearchAcoustic sensing and communication are essential tools for many scientific research endeavors in underwater environments. Scientists use acoustic sensors to measure a wide range of physical and biological parameters, including ocean currents, temperature, and the behavior of marine organisms. Acoustic communication can also be used to study the behavior of marine mammals and fish, as well as for the positioning and tracking of objects and equipment in the ocean.B. Military ApplicationsUnderwater acoustics also has important applications in military operations. For example, acoustic sensors can be used for underwater surveillance and detection of submarines and other vessels. Acoustic communication can also be used for secure and reliable communication between submarines and other vessels.C. Commercial ApplicationsUnderwater acoustics plays a vital role in a number of commercial applications, including oil and gas exploration, underwater resource management, and underwater construction. Acoustic sensing can be used to identify and map underwater resources, while acoustic communication can be used to manage underwater assets and ensure safe operation of underwater construction equipment.D. Environmental MonitoringAcoustic sensing and communication are also useful tools forenvironmental monitoring in underwater environments. For example, acoustic sensors can be used to monitor ocean acidification, harmful algal blooms, and other environmental parameters. Acoustic communication can also be used to transmit real-time data on environmental conditions, as well as to control and monitor underwater environmental remediation efforts.E. Underwater NavigationAnother important application of underwater acoustics is in navigation. Acoustic sensing can be used to measure underwater topography and detect underwater hazards, while acoustic communication can be used to transmit navigation instructions and coordinate movement of underwater vehicles.F. Underwater EntertainmentFinally, underwater acoustics can also be used for entertainment purposes, such as underwater performances or exhibitions. Acoustic communication can be used to transmit music and other sounds to underwater audiences, and acoustic sensing can be used to monitor the behavior of aquatic animals in response to underwater events.In conclusion, underwater acoustics has a wide range of applications in scientific, military, commercial, environmental, navigation, and entertainment contexts. Continued research and development in underwater acoustics will enable new and innovative applications and improve the accuracy and reliability of underwater communication and sensing systems.V. Challenges andFuture Directions in Underwater AcousticsDespite the many applications of underwater acoustics, there are still significant challenges that must be addressed in order to improve the accuracy and reliability of underwater communication and sensing systems. In this section, we will explore some of these challenges and potential future directions in underwater acoustics research.A. Signal Propagation ChallengesOne of the main challenges in underwater acoustics is the highly variable nature of the underwater environment. Sound waves can be distorted, absorbed, or reflected as they pass through different types of materials, such as seawater, sediment, and marine life. This leads to challenges in signal propagation and can limit the range and resolution of underwater acoustic communication and sensing systems.To address these challenges, researchers are exploring new signal processing techniques and materials to improve the accuracy and range of underwater signal transmission. In addition, advances in robotics and autonomous systems are enabling researchers to better explore the underwater environment and gather more accurate data for signal propagation models.B. Interference and NoiseIn addition to signal propagation challenges, another significant challenge in underwater acoustics is interference and noise. Inparticular, noise from human activities such as shipping, drilling, and sonar can interfere with underwater communication and sensing systems, making it difficult to distinguish signals from ambient noise.To address these challenges, researchers are exploring new signal processing techniques and noise-reduction algorithms, as well as developing underwater acoustic sensors that are designed to be more robust in noisy environments.C. Power and Energy ChallengesUnderwater acoustic communication and sensing systems also face significant power and energy challenges. Traditional battery-powered systems are often limited by the lifespan of the batteries, which can make long-term monitoring and sensing difficult and costly.To address these challenges, researchers are exploring new energy-harvesting technologies that can generate power from renewable sources such as wave and tidal energy, as well as developing more efficient and low-power communication and sensing technologies.D. Integration and StandardizationFinally, another challenge in underwater acoustics is the need for improved integration and standardization of acoustic communication and sensing systems. There is currently a lack of common standards and protocols for underwater acoustic communication and sensing, which can limit interoperabilitybetween different systems.To address these challenges, researchers and industry stakeholders are working to develop common standards and protocols for underwater acoustic communication and sensing, as well as exploring new approaches to system integration for improved performance and reliability.In conclusion, underwater acoustics is a rapidly evolving field with many exciting applications and opportunities for innovation. Continued research and development in signal processing, energy harvesting, and system integration will be essential for overcoming the challenges facing underwater communication and sensing, and for unlocking new possibilities in scientific research, resource management, and exploration of the underwater environment.。
基于浅海声信道特征测量的舰船水下辐射噪声源级获取方法
宇航计测技术Journal of Astronautic Metrology and Measurement2021年2月第41卷第1期Feb. ,2021Vol. 41, No. 1文章编号.1000-7202(2021)01 -0095-06 DOI ： 10.12060/j. issn. 1000-7202.2021.01.17基于浅海声信道特征测量的舰船水下辐射噪声源级获取方法刘玉财陈毅易文胜 (杭州应用声学研究所，浙江杭州310023)摘要针对浅海信道环境下舰船水下辐射噪声测量问题，介绍了一种基于水域声信道传播特征的舰船噪声源级工程测试方法，该方法通过多基元空间能量平均方法来实现。
通过探讨以能量平均声压级曲线来表征浅水 域水下声传播特征,提出了一个适用于浅水域声传播规律的计算经验公式。
对所提测量方法的可行性和准确性进行了仿真分析和湖上试验，结果证明了采用空间能量平均处理方法可以很好的抑制因浅水域声场起伏而带来的高 测量误差，对于提高舰船水下辐射噪声测量的准确性具有一定的参考价值。
关键词声源级舰船噪声浅海信道中图分类号:0427.5 文献标识码:AMethod for Acquiring Ship Underwater Noise Source Level based on Measurement of Shallow Sea Acoustic Channel CharacteristicsLIU Yu-cai CHEN Yi YI Wen-sheng(Hangzhou Applied Acoustics Institute , Hangzhou 310023, China )Abstract This paper introduces a ship noise source-level engineering test method based on the propagationcharacteristics of the water acoustic channel to solve the problem of ship underwater radiated noise measurement in theshallow water channel environment. The method is realized by the multi-element space energy averaging, the energy average sound pressure level curve is used to express the characterize of underwater sound propagation in shallow water, and acalculation experience formula suitable for the law of sound propagation in shallow water is proposed. The feasibility andaccuracy of the proposed measurement method are verified by simulation and lake experiments. The results prove that the space energy average processing method can suppress the high measurement error caused by the fluctuation of the sound fieldin shallow water,this method has certain reference value for improving the accuracy of ship radiated noise measurement.Key words Sound source Level Ship noise Shallow sea Acoustic channel1弓| 言舰船水下辐射噪声对舰船的战场生存和武器装备性能都有着重大影响，是评价舰船作战能力及隐蔽 舰船是各国海军战略威慑力量的重要组成。
浅海中低频水声信道仿真研究
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浅海水声信道模型分析及频率选择性衰落仿真
第10卷第12期Vo l .10,No .12宜宾学院学报J ou rnal of Yibin Un i versity2010年12月Dec .,2010收稿日期1修回作者简介贺繇(),男,重庆江津人,工学硕士,讲师,主要从事信号与图像处理、遥感方向研究浅海水声信道模型分析及频率选择性衰落仿真贺繇(宜宾学院物理与电子工程学院,宜宾644000)摘要:水声通信是以声波信号作为载波的水下通信,水声信道是水下通信的重要组成部分.在浅海中,水声信道是通信环境恶劣的信道,存在着较强的频率选择性衰落.通过对浅海水声信道的分析、建模、仿真,验证了水声信道的频率选择性衰落.关键词:水声信道;频率选择性衰落;射线声学模型中图分类号:T N92913 文献标志码:A 文章编号:1671-5365(2010)12-0078-03Ana lysis of Under wa ter Acou stic Cha nne lsM odel a nd S i m u l a tion of F requen cy Se lect i v ity A tten ua tionHE Yao(College of Physics and Electronic Engineering,Yibin Un iversity,Yibin 644000,China)Ab stract:The under water acou stic co mmun icati on is the under w ater commun icati on adop ted the acoustic signal as its carrier,and the under w ater acou stic channel is an i mpo rtan t p art of the under water ac ou stic c ommunication.Ho wever,the channel is a bad co mmun icati on channel in the shallo w sea and there is str ong frequency selectivity attenuation .Based on the analysis,modeling,si mu lating,the frequency selectivity attenuation of the under water commun icati on channels was p r oved.K ey word s:under water acoustic channels;frequency selectivity attenuati on;ac ou stic ray model 由于经济发展和国防建设的需要,人类活动已经频繁在水下展开,民用领域有水下的资源探测和开采、水下环境监测、海洋空间的利用;军事领域有潜艇在巡逻、演习、作战时与水面舰只或陆上基地的通信联络等,这些活动都必须建立可靠的通信互联,所以,水下通信,特别是人类活动最为频繁的浅海水域的水下通信是研究的重点领域之一.1 浅海水声信道的基本情况空间无线通信都采用高频电磁波作为信息传输的载波,一般都具有传播速度快、传播时延小、多普勒频移小、带宽较宽的特点.但是在水下,电磁波传输衰减极快,传播距离很短,所以电磁波不适合作为水下通信的载波.而声波在水下以纵波的方式进行传播,衰减速度比电磁波慢得多,传播距离较远,是水下通信较为理想的载波[1].即使以声波作为水下通信的载波,水下通信仍然存在诸多的技术难题.声波在水中传输时,水将对声波产生较强的吸收作用,使声波能量严重衰减.同时,声波信号在水中传输将经历多次海面和海底的反射,到达接收端的信号是从不同方向和不同路径传来,多径效应明显.在浅海中,由于浅海海底的复杂构成、海面的风浪、海水在不同季节由于温度原因形成的不同温度梯度等因素影响,多径效应将进一步增强,声波在传播过程中的能量衰减更为严重.声波信号的发射端和接收端可能存在相对运动,这将会导致接收机接收到的信号发生频率变化的多普勒效应.即使发送端和接收端静止,由于海面存在波浪运动和海中存在各种湍流,声波在行进过程中被海面波浪的调制,到达接收端时频率也会产生变化[2].所以,水声信道必须考虑多普勒效应.水声信道特别是浅海水声信道中的环境噪声比较严重,包括海潮、湍流、海面刮风下雨、生物群体活动、船舶航行和石油钻探都会对水声信道产生较强的噪声干扰.所以,水声信道是一复杂多变的信道,具有衰减严重、多径效应和频散特性较强、环境噪声严重的特点.正是水声信道的复杂性和不稳定性,使其成为自然界中最复杂的无线通信信道[3].水声信道在传输通信信号的过程中,将出现较强的频率选择性衰落、时间选择性衰落和码间干扰.2 声波频率的选择用声波作为水下通信的载波时,频率不能太低,因为太低的频率意味着通信速率很低.所以,水下通信的声波载波频率都在1KHz 以上[4].当频率大于1K H z 的声波在水中传播时,能量的衰减主要是由于水对声波的吸收.其中海水对声波的吸收系数为[2]:2010-10-24:2010-10-24:1972-k0=0.11f21+f2+44f24100+f2其中f的频率是KH z,k的单位是分贝/公里.由上面的公式可以看出,频率越高,海水对声波的吸收越强,对1KH z声波的吸收系数是0.065分贝/公里;对30KHz声波,吸收系数约为8分贝/公里;到50KHz时,吸收系数已达16.8分贝/公里.所以水下通信采用的声波信号频率一般为50KH z以下,信道带宽很有限.3 射线声学模型水声信道作为具有时变、频变、空变特性的通信环境恶劣的信道,很难用简单精确的数学模型将其表示,大部分研究采用的是基于射线声学理论的射线模型.射线模型是波动理论的一种近似,它直观地描述了声能量在介质中的传播,将声波看作是无数条垂直于等相位面的声线向外传播[5],其中每一条声线都携带着发射信号的信息.声能量从声源出发,在空间沿着声线按一定规律到达接收点,接收点收到的声能是所有到达的声能的叠加[2].在水声信号传输的过程中,有五种典型的声线,一是直达路径声线D;二是由发射端出发,首次反射是经过海面,到达接收端前的最后一次反射也是经海面,总共经过了n次海面反射才到达接收端的声线SS n;三是由发射端出发,首次反射是经过海面,到达接收端前的最后一次反射经海底,总共经过了n次海底反射才到达接收端的声线SB n;四是由发射端出发,首次反射是经过海底,到达接收端前的最后一次反射经海面,总共经过了n次海面反射才到达接收端的声线BS n;五是由发射端出发,首次反射是经过海底,到达接收端前的最后一次反射也是经海底,总共经过了n次海底反射才到达接收端的声线BB n.如图1所示,图中只画出了直达声线和n=1的反射声线.图1 声线传播图 在利用声学射线模型分析水声信道模型时,为了简化问题,需假设若干理想条件:1)所有声线为直线.在水温及海水自身产生压力的影响下,水中声速不会恒定,这将导致声线在水中发生轻微弯曲为简化模型,在声线传播图中,我们都用直线来表示声线传播方向)水深为常数对于大陆架附近的海域,海底的深度是平缓变化的,为简化模型,假设浅海水深为固定常数.3)在声波由海底反射时,海底会吸收一部分能量,这里假设海底的反射系数近似为0.85.同时,声波经过海底反射时,产生相移180°.4)海面的反射系数只与海面的风速和载波频率有关.在声波发射端与接收端距离比发射端与接收端深度大得多的情况下,海面的反射系数公式为rs=1+(f/f1)21+(f/f2)2其中f2=378w-2,f1=10f2,其中f是载波频率,w是风速[2].4 接收端接收信号的相关计算直达声线的传播距离D=L2+(h1-h2)2.首次反射和最后一次反射均通过海面的声线传播距离为SSn=L2+(2nH-h1-h2)2.首次反射和最后一次数反射均通海底的声线传播距离为BB n=L2+[2(n-1)H+h1+h2)2首次反射经过海面,而最后一次反射经过海底的声线传播距离为SBn=L2+(2nH-h1+h2)2,首次反射经过海底,而最后一次反射经过海面的声线传播距离为BS n=L2+(2nH+h1-h2)2,声波经过直达路径D的传播时间为:t0=D/c,声波经过经SSn的传播时间为tSS n=SSn/c,声波经过BBn的传播时间为tBB n=BBn/c,声波经过SBn的传播时间为tS B n=SBn/c,声波经过BSn的传播时间为tBSn=BSn/c,声音的传播损耗主要由海水对声音的吸收、海面反射损失、海底反射损失和扩散损失组成.由于本模型已认扩散损失按距离衰减,为简化问题,将海面和海底的联合衰减系数定义为k SSn=-(r b)n-1(r i)n=-0.85n-1(r S)nkBB n=-(rb)n(rS)n-1=-0.85n(rS)n-1kS B n=(rb)n(rS)n=0.85n(rS)nkBSn=(rb)n(rS)n=0.85n(rS)n式中的rb为海底的反射系数,假设其为0.85,负号为声波相位改变180°.因此,接收端的信号可表示为r(t)=∑∞i=1kix(t-τi)其中k i表示第i条路径相对于直达路径的归一化衰减因子考虑到海水对声波的吸收作用,设海水对声音的吸收系数为,则不同路径对声音信号的吸收系数为97 第12期 贺繇:浅海水声信道模型分析及频率选择性衰落仿真..2..k0k SS n=DSS nk S S nk 0k BB n=DBB n k BB nk 0k S B n=DSB nk SB nk 0k BS n=DBS nk B S nk 0则接收端的信号最后可写为[2]:r(t)=1+∑∞n=1[k SS ne-t S S+k BB n e-t BB+k S B ne-t BB]5 信道模型仿真通过Matlab 软件,仿真在水深为80米的浅海中,将水声发射器置于水下65米、水声接收器置于水下50米,在水平相距2公里和20公里处,发射不同频率的正弦波信号,接收端收到信号的情况.通过仿真图形可以看出:随着距离的增大,接收端接收到的信号越来越微弱,在2公里处的接收机和20公里处的接收机接收到的信号强度差别很大,说明声波在传输过程中衰减很强.不管是在2公里距离上还是在20公里距离上,接收机接收到的信号都随着频率的不同而幅度各不相同,出现了频率选择性衰落,在2公里距离上的频率选择性衰落强于20公里距离上的频率选择性衰落.这说明浅海水声信道对不同频率的声波衰减不同,并且距离越近,频率选择性衰落越明显.这是由于收发端距离较近时,接收端能够接收到声线较多,多个路径信号相互抵消和迭加引起的信号幅度起伏较为剧烈;而在收发端距离较远时,接收端接收到的声线数量较少,并且到达的声线都已经历较强的衰减,所以此时引起接收端信号的起落较为平缓.图2 接收机在2公里处接收到的信号图3 接收机在20公里处接收到的信号 综上所述,浅海水声信道是一个复杂多变的信道,具有较强的频率选择性衰落特征.同时,水声信道的码间干扰、浅海背景噪声和有限的带宽,使浅海水声信道成为了迄今最为复杂的无线通信信道之一.浅海水声信道的研究,必须综合信号处理、声学、海洋学、通信技术等多学科知识才能取得较好的进展.参考文献:[1]蔡惠智,刘云涛,等.水声通信及其研究进展[J ].物理,2006,35(12):1038-1043.[2]许俊.水声语音通信研究[D ].厦门:厦门大学,2001:15-33.[3]魏莉,许芳,孙海信.水声信道的研究与仿真[J ].声学技术,2008,27(1):25-29.[4]孙博,程恩,欧晓丽.浅海水声信道研究与仿真[J ].无线电通信技术,2006(3):11-15.[5]李蓉艳,杨坤德,邹士新.多输入多输出浅海水声信道响应的盲估计[J ].同济大学学报(自然科学版),2007,35(5):664-668.【编校:李青】8 宜宾学院学报 第10卷 。
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基于射线模型的浅海水声传播仿真研究
作者：黄建强鞠建波
来源：《现代电子技术》2011年第18期
摘要：浅海是我国船只活动的主要区域，在计划海上实验、设计最优声纳系统和预测海上声纳性能时，水声模型被广泛地应用于预报声学环境。
用射线模型为浅海声场建模，由于射线理论有足够的准确性，可以用来获得声波在空间传播的重要信息，在一定的条件下，射线声学的数学运算也比较简捷。
在此结合仿真结果，证明了由射线理论给出的声线图可以给声场以直观、形象的理解，其建立的水声信道模型在工程应用上具有重要意义。