Sound-pressure level calculations using the RRA algorithm fordepth-dependent speeds of sound valid at turning points and focal points

Sound-pressure level (SPL) calculations are made along individual ray paths for arbitrary, one-dimensional, depth-dependent speeds of sound using an enhanced version of the RRA (recursive ray acoustics) algorithm. The SPL calculations are valid (i.e., finite) at turning points and focal points and do not require the use of Airy functions. The SPL calculations include the effects of frequency-dependent volume attenuation and frequency-dependent attenuation due to surface and bottom reflections. The ocean surface and bottom are treated as boundaries between viscous fluid media. Although the ocean surface is modeled as a planar boundary, the bathymetry is an arbitrary function of horizontal range. Sound speed versus depth and bathymetric data are represented by orthogonal function expansions. Computer simulation results from preliminary test cases are presented     

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。     

水声定位系统中迭代适应点分层的声线修正算法

水声定位系统中, 声线弯曲是造成定位误差大的主要原因, 本文针对该问题提出了一种迭代适应点分层(IAPL)的声线修正算法, 将声速剖面筛选分层修正声线。首先搭建水声定位模型, 通过拟合目标海域的监测数据, 得到声速高次函数; 其次探究声线弯曲时目标位置与掠射角的关联性, 由此构造出声线插值函数并求解路径参数; 最后提出划分原则, 精简声速剖面分层。仿真结果表明, 所提算法定位误差较低, 分层精简率均维持在48.04%的水平, 使计算量平均下降可达50.27%, 能够最大程度保留声速剖面的原始特征, 减少分层数量, 提高计算效率。     

The coupled oceanographic–tomographic analysis and prediction system: A practical means for utilizing high frequency tomography in the world's oceans

Details are presented of a methodology that utilizes acoustic travel time information in an ocean circulation model. Recent developments of this model-oriented tomography are discussed, representing some significant improvements over earlier formulations. More accurate means of determining the arrival times of specific ray paths are detailed, along with a means of estimating possible errors in the calculated travel times. The assimilation of the observed arrival time information into an ocean model is achieved using a Kalman gain, and more advanced expressions for calculating the Kalman gain are presented. A formulation to account for errors in the stated positions of a source and receiver is also presented. It is shown that the methodology performs fairly well in reproducing observed travel time anomalies. However, the model-predicted anomalies along a specific ray path may not always track the observed anomalies for that path when assimilating multiple ray path data. Results indicate that additional work is required to determine a means of handling observed arrival time data without having prior knowledge of the magnitude of errors in the observations. Results from simulation experiments provide estimates of: (1) potential errors when the travel times for ray paths are only sampled at discreet intervals as opposed to continuously and (2) to what degree acoustic data can be expected to “correct” model-predicted fields.     

一种基于改进蚁群算法的载人潜水器全局路径规划

当前关于使用蚁群算法解决载人潜水器路径规划问题的研究,往往只注重路径的长度和算法收敛速度,容易忽略路径点与障碍物之间的距离和路径的平滑度等要素。载人潜水器过于靠近障碍物航行时容易产生碰撞;按照不平滑路径行驶时,频繁地转向会降低航行效率。为解决这些问题,受人工势场法启发,文中在蚁群算法的概率选择环节引入障碍物惩罚因子φ和转向惩罚因子ψ,对路径点的选择加以限制。仿真测试表明,相比于传统蚁群算法和Dijkstra算法,该算法规划的路径与障碍物之间保持安全距离且转向次数更少,因此载人潜水器按照此路径航行时,安全性和航行效率更高。     

基于改进量子粒子群算法的AUV路径规划研究

针对海洋环境下自主水下机器人（AUV）的路径规划问题,提出了一种基于框架四叉树的改进量子粒子群算法（QPSO）,首先使用框架四叉树的方法对障碍物建模,该方法提高了建模的精度且对后续算法的效率也有极大的改进,之后设计改进的量子粒子群算法,并且结合水下环境的特殊性设计适应度函数,综合考虑航线路径长度、偏转角度以及海流影响,使得算法可以在水下环境中寻得能耗最短的解路径。最后通过仿真试验验证,相比于传统的栅格法和粒子群算法,改进量子粒子群算法的运算时间更短,收敛速度更快,其独特的适应度函数可以使AUV能更好适应水下多变的环境,且能利用海流设计能耗更小的路径,具有很大的实用价值。     

Ray Theory Application in Long Baseline System

The long baseline (LBL) system is widely used to locate and track autonomous underwater vehicles (AUV) through acoustic communication.Three important issues are presented here in LBL system application with AUV.Those issues which regard the normal acoustic communication between LBL system and AUV are the depth of towed array,the length of beacon cable,and the effective area of the AUV.The first issue is the key of the LBL system,which ensures the normal communication between towed array and beacons.The second issue which impacts the normal communication from the AUV to beacons in available range should be considered after the first one has been settled.Then the last issue determines the safe work area of the AUV.The ordinary differential equations (ODE) algorithm of ray is deduced from Snell′s law.The ODE algorithm is applied to obtain sound rays from sound source to receiver.These problems are solved by the judgment that whether rays pinging from a sound source arrives at a receiver.The sea trial shows that these methods have much validity and practicality.     

A technique for autonomous underwater vehicle route planning

If an underwater vehicle is to be completely autonomous, it must have the ability to plan paths around obstacles in order to operate safely. Many solutions to the problem of planning the path of a robot around obstacles have been proposed, but all are limited in some way. An algorithm using artificial potential fields to aid in path planning is presented. The planning consists of applying potential fields around obstacles and using these fields to select a safe path. The advantage of using potential fields is that they offer a relatively fast and effective way to solve for safe paths. A trial path is chosen and then modified under the influence of the potential field until an appropriate path is found. By considering the entire path, the problem of being trapped in a local minimum is greatly reduced, allowing the method to be used for global planning. The algorithm was tried with success on many different planning problems. The examples provided illustrate the algorithm's application to two- and three-dimensional planning problems     

基于辛几何算法的高斯束叠前深度偏移

辛几何算法是专门针对动力学过程设计的算法,以提高动力学问题求解的精度与效率。高斯束偏移过程中的运动学与动力学射线追踪,从物理上讲是一个动力学过程,可以利用辛几何算法对其进行优化。本文将基于辛几何算法的运动学射线追踪引入高斯束叠前深度偏移中,并在推导了动力学射线追踪方程组的辛差分格式基础上,实现了基于辛几何算法的高斯束叠前深度偏移。模型实验表明,基于辛几何算法的运动学射线追踪,其效率与精度相比常规算法都具有一定优势,而基于辛几何算法的高斯束叠前深度偏移方法能够对复杂构造模型精确成像。     

Closed-loop randomized kinodynamic path planning for an autonomous underwater vehicle

A randomized kinodynamic path planning algorithm based on the incremental sampling-based method is proposed here as the state-of-the-art in this field applicable in an autonomous underwater vehicle. Designing a feasible path for this vehicle from an initial position and velocity to a target position and velocity in three-dimensional spaces by considering the kinematic constraints such as obstacles avoidance and dynamic constraints such as hard bounds and non-holonomic characteristic of AUV are the main motivation of this research. For this purpose, a closed-loop rapidly-exploring random tree (CL-RRT) algorithm is presented. This CL-RRT consists of three tightly coupled components: a RRT algorithm, three fuzzy proportional-derivative controllers for heading and diving control and a six degree-of-freedom nonlinear AUV model. The branches of CL-RRT are expanded in the configuration space by considering the kinodynamic constraints of AUV. The feasibility of each branch and random offspring vertex in the CL-RRT is checked against the mentioned constraints of AUV. Next, if the planned branch is feasible by the AUV, then the control signals and related vertex are recorded through the path planner to design the final path. This proposed algorithm is implemented on a single board computer (SBC) through the xPC Target and then four test-cases are designed in 3D space. The results of the processor-in-the-loop tests are compared by the conventional RRT and indicate that the proposed CL-RRT not only in a rapid manner plans an initial path, but also the planned path is feasible by the AUV.     

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。     

Jason Microwave Radiometer Performance and On-Orbit Calibration

Results are presented from the on-orbit calibration of the Jason Microwave Radiometer (JMR). The JMR brightness temperatures (TBs) are calibrated at the hottest and coldest ends of the instrument's dynamic range, using Amazon rain forest and vicarious cold on-Earth theoretical brightness temperature references. The retrieved path delay values are validated using collocated TOPEX Microwave Radiometer and Radiosonde Observation path delay (PD) values. Offsets of 1–4 K in the JMR TBs and 8–12 mm in the JMR PDs, relative to TMR measurements, were initially observed. There were also initial TB offsets of 2 K between the satellite's yaw state. The calibration was adjusted by tuning coefficients in the antenna temperature calibration algorithm and the antenna pattern correction algorithm. The calibrated path delay values are demonstrated to have no significant bias or scale errors with consistent performance in all nonprecipitating weather conditions. The uncertainty of the individual path delay measurements is estimated to be 0.74 cm ± 0.15, which exceeds the mission goal of 1.2 cm RMS.     

Jason Microwave Radiometer Performance and On-Orbit Calibration

Results are presented from the on-orbit calibration of the Jason Microwave Radiometer (JMR). The JMR brightness temperatures (TBs) are calibrated at the hottest and coldest ends of the instrument's dynamic range, using Amazon rain forest and vicarious cold on-Earth theoretical brightness temperature references. The retrieved path delay values are validated using collocated TOPEX Microwave Radiometer and Radiosonde Observation path delay (PD) values. Offsets of 1-4 K in the JMR TBs and 8-12 mm in the JMR PDs, relative to TMR measurements, were initially observed. There were also initial TB offsets of 2 K between the satellite's yaw state. The calibration was adjusted by tuning coefficients in the antenna temperature calibration algorithm and the antenna pattern correction algorithm. The calibrated path delay values are demonstrated to have no significant bias or scale errors with consistent performance in all nonprecipitating weather conditions. The uncertainty of the individual path delay measurements is estimated to be 0.74 cm ± 0.15, which exceeds the mission goal of 1.2 cm RMS.     

Path following control system for a tanker ship model

A two-dimensional path following control system for autonomous marine surface vessels is presented. The guidance system is obtained through a way-point guidance scheme based on line-of-sight projection algorithm and the speed controller is achieved through state feedback linearization. A new approach concerning the calculation of a dynamic line-of-sight vector norm is presented which main idea is to improve the speed of the convergence of the vehicle to the desired path. The results obtained are compared with the traditional line-of-sight scheme. It is intended that the complete system will be tested and implemented in a model of the “Esso Osaka” tanker. The results of simulations are presented here showing the effectiveness of the system aiming in to be robust enough to perform tests either in tanks or lakes.     

A simulation tool for high data-rate acoustic communication in ashallow-water, time-varying channel

The paper discusses the development of a simulation tool to model high data-rate acoustic communication in shallow water. The simulation tool is able to generate synthetic time series of signals received at a transducer array after transmission across a shallow-water communication channel. The simulation tool is suitable for testing advanced signal processing techniques for message recovery. A channel model has been developed based on the physical aspects of the acoustic channel. Special emphasis has been given to fluctuations of the signal transmission caused by time-varying multipath effects. At shorter ranges, the temporal variations are dominated by acoustic scattering from the moving sea surface. Therefore, the channel model produces a coherence function which may be interpreted as a time-varying reflection coefficient for the surface scattered acoustical path. A static, range-independent ray model identifies the significant multipaths, and the surface path is modulated with the time-varying reflection coefficient. The advantages and limitations of the channel model are discussed and assumptions necessary to overcome the limitations are emphasised. Based on the assumptions, an algorithm has been developed and implemented to model how a binary message will be modulated when transmitted by a transducer, is distorted in the channel and finally is received by a transducer array     

INFLUENCE OF SEDIMENT SOUND VELOCITY ON TIME-FREQUENCY CHARACTERISTICS OF THE SIGNAL IN THE DEEP SEA

This paper uses acoustical method to obtain the sound speed structure information of the deep sea sediment. The time-frequency characteristics of the explosive sound signals in the deep sea are analysed by using the narrow-band filters, and the bottom-reflecting path and bottom-refracting path are separated in time domain. Based on the two kinds of selected bottom models the travel-time difference between the two paths mentioned above is calculated according to the ray theory, and simple analytical formulae are obtained. The bottom model, which is more suitable for the experimental area, is identified by comparing the theoretical with experimental travel-time differences versus range.     

顾及恶劣海况的船舶救援路径规划

为了保障救援船舶在恶劣海况环境下能够安全、高效地到达救援区域,本文改进人工鱼群算法开展海上救援路径规划研究.选取地形、海风和海浪等指标进行风险度量,采用GIS(geographical infor-mation system)多指标决策方法构建海洋环境威胁场,通过粒子群算法计算救援路径规划的最佳参数,并实现海上救援路径...     

Three-dimensional ray acoustics: new expressions for the amplitude,eikonal, and phase functions

New three-dimensional ray-acoustics expressions for the amplitude, eikonal, and phase along a ray path are derived. These expressions clearly indicate the numerical calculations that must be performed in order to evaluate these functions. The ocean medium is characterized by a three-dimensional random index of refraction which is decomposed into deterministic random components     

关于多波束声速剖面改正问题的探讨

简要介绍了声线跟踪计算中比较精确的常梯度声线跟踪算法,针对实际声速剖面测量中可能出现的随机误差和整体偏差两种情况,分别设计了相对应的模拟声速剖面,然后采用常梯度声线跟踪算法计算波束脚印,分析声速剖面误差对波束脚印计算的影响,给出了实际多波束测量作业中声速剖面测定密度和间隔的建议。     

基于DIDSON的未知海域覆盖规划算法

针对自主水下机器人的路径规划问题,提出一种基于双频识别侧扫声呐(DIDSON)的全局路径规划算法。根据双频识别侧扫声呐的物理特性对AUV进行数学建模,根据声呐的工作频率不同,将AUV分为高频、低频两种工作模式。高频模式下成像精度高,低频模式下成像范围大。文中提出了一种D2-CPP算法,根据声呐返回的识别结果,算法会自主切换AUV的工作模式,并动态规划出对应的路径点,直到覆盖所有区域。通过与割草机算法的仿真对比,证明了算法的有效性,近海实验证明了算法的可靠性。