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1.
This paper deals with the basic modeling problem in underwater acoustics that is the characterization of the channel between a transmitter and a receiver. The problem is analyzed here using an array of sensors that receive PSK signals emitted by several sources. Data come from an experiment realized by a physical system situated in the Mediterranean Sea. In order to identify the multipath channel, we need to access the propagation time delay and the angle of arrival of each propagation ray. However, many of these acoustic ray paths are too close to be separated by classic processing methods (matched filter, beamforming, etc.); new methods with better resolution must be applied in order to analyze the experimental signals and to determine their arrival time on the array of sensors. After a presentation of this problem, we will first discuss high-resolution methods that are usually applied in the localization problem; we will then focus on wavelet packet analysis which provides good results by improving the temporal resolution of acoustic signals 相似文献
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《中国海洋工程》2020,(3)
In order to clarify the distribution and variation of silt and fluid mud in the Waiganmen shallow section of the 50000-ton intake channel of the Xiangshan Port, and to understand the influence of the channel excavation on the surrounding flow conditions and the strength of the backsilting, especially the impact of typhoon on the sudden silting of the channel, so as to demonstrate the feasibility and stability of the channel excavation. The fluid mud,hydraulic, sediment and topographic measurements were carried out in the study area, and the thickness of the fluid mud layers, tidal current, sediment and topographic data were obtained. Dual-frequency sounder, gamma-ray densitometer and SILAS navigational fluid mud measurement system were used to monitor the fluid mud, and the results were compared and verified. The adaptability and accuracy of the three methods were analyzed. The SILAS navigational continuous density measurement system and gamma-ray fixed-point fluid mud measurement are used to detect the density, thickness and variation of the fluid mud accurately. Based on the hydrological observation data,the process of erosion and deposition in excavation channel and its influence mechanism are analyzed, and the distribution characteristics and evolution law of siltation in engineering area are given in the form of empirical formula. The research shows that the super typhoon can produce large siltation, which results in sudden siltation of the channel. The tidal current is the main dynamic factor of the change of erosion and siltation of the excavation trench. Under the influence of reciprocating tidal current and excavation topography, the trial excavation trench is silted on the whole. There is fluid mud in the monitoring area of the trench, and the distribution of fluid mud is different in space. The thickness of the fluid mud at the bottom of the trench is generally larger than that outside the trench and the slope of the trench, and the siltation of the trench tends to be slow. The research results can provide scientific evaluation for channel excavation and maintenance, and support for the implementation of the project. 相似文献
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Two adaptive algorithms for multipath time delay estimation 总被引：1，自引：0，他引：1
The problem of time delay estimation (TDE) with multipath transmissions arises often in many sonar and radar systems. Two adaptive algorithms based on a parameter estimation approach are proposed to estimate the difference in arrival times of a signal at two separated sensors in the presence of multipath propagation. The first method uses an adaptive IIR filter to eliminate the multipath signal in each transmission channel prior to applying a constrained delay estimation algorithm to extract the time difference between the two received outputs. The second employs two constrained adaptive FIR filters to perform equalization of the multipath arrivals, and time delay is then derived using a constrained delay estimator similar to that in the first method. Computer simulations are presented to compare and contrast the tracing capability and convergence behavior of these multipath TDE methods 相似文献
5.
淤泥质、粉沙质及沙质海岸航道回淤统一计算方法 总被引：1，自引：0，他引：1
根据20世纪80年代初提出的淤泥质海岸航道回淤计算方法的基础上,开展了拓展研究,使之统一适用于淤泥质海岸、粉沙质海岸及沙质海岸。主要研究内容有,在波浪和潮流综合作用下挟沙力含沙量研究中引入了特定的泥沙因子F1/F,从而挟沙力含沙量公式不仅适用于淤泥质泥沙,也适用于非淤泥质泥沙;在动力因素方面,除了一般寻常潮和波浪动力外,进一步考虑了风暴潮和破波的巨大掀沙能力造成航道骤淤的可能性。并结合连云港30万吨级主航道扩建及徐圩港区10万吨级航道的回淤问题(包括骤淤可能性问题),京唐港外航道和黄骅港外航道的骤淤问题,进行预测计算及校验计算,结果都是良好的。此外,对杭州湾强潮和涌潮情况下的挟沙力含沙量也进行了校验计算,结果也非常满意。 相似文献
6.
Mikhalevsky P.N. Gavrilov A.N. Baggeroer A.B. 《Oceanic Engineering, IEEE Journal of》1999,24(2):183-201
In April 1994, coherent acoustic transmissions were propagated across the entire Arctic basin for the first time. This experiment, known as the Transarctic Acoustic Propagation Experiment (TAP), was designed to determine the feasibility of using these signals to monitor changes in Arctic Ocean temperature and changes in sea ice thickness and concentration. CW and maximal length sequences (MLS) were transmitted from the source camp located north of the Svalbard Archipelago 1000 km to a vertical line array in the Lincoln Sea and 2600 km to a two-dimensional horizontal array and a vertical array in the Beaufort Sea. TAP demonstrated that the 19.6-Hz 195-dB (251-W) signals propagated with both sufficiently low loss and high phase stability to support the coherent pulse compression processing of the MLS and the phase detection of the CW signals. These yield time delay measurements an order of magnitude better than what is required to detect the estimated 80-ms/year changes in travel time caused by interannual and longer term changes in Arctic Ocean temperature. The TAP data provided propagation loss measurements to compare with the models to be used for correlating modal scattering losses with sea ice properties for ice monitoring. The travel times measured in TAP indicated a warming of the Atlantic layer in the Arctic of close to 0.4°C, which has been confirmed by direct measurement from icebreakers and submarines, demonstrating the utility of acoustic thermometry in the Arctic. The unique advantages of acoustic thermometry in the Arctic and the importance of climate monitoring in the Arctic are discussed. A four-year program, Arctic Climate Observations using Underwater Sound is underway to carry out the first installations of sources and receivers in the Arctic Ocean 相似文献
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1 .Introduction Underwater acoustic (UWA) communicationis a fast developingfield,and its applicationis notlimitedto military affairs ,but is also extendinginto commercial fields .Catipovic (1990) ,Stojanovic(1996) and Kilfoyle and Baggeroer (2000) pointed… 相似文献
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《Coastal Engineering》2001,43(1):59-74
This paper presents a study of the siltation process in an access channel to a port through analysis of environmental data, viz. waves, tidal currents, sediment characteristics, silt concentration and siltation at site. A rational methodology has been presented to co-relate environmental data and siltation quantity, judiciously applying the various theories available to wave propagation, littoral current, sediment transport and its trapping. The efficacy of the method is then tested to simulate the observed siltation in different phases of its development in terms of widening and deepening of the channel. It is observed that estimation of the representative environmental parameters is very important as the data collected over a long period show wide variation since sediment transport formulae available are very sensitive to these parameters. An attempt has been made in this paper to understand the mechanism of siltation in the approach channel to the port. 相似文献
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粉沙质海岸泥沙运动特性研究 总被引：2，自引：1，他引：1
文章对粉沙质海岸的泥沙运动特性进行了系统、全面的研究.从5个方面进行了论述:粉沙质海岸的界定、泥沙基本水力特性、泥沙运移型态、航道骤淤的统计特性和航道淤积计算.提出粉沙质海岸的界定应综合考虑泥沙平均中值粒径、黏土含量和泥沙粒径分选性三方面因素;泥沙基本水力特性是起动流速小、沉降速度大、沉积密实快,泥沙运动十分活跃;泥沙... 相似文献
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水声信道的多径时延扩展和时变特性对信道估计和均衡技术的研究带来了很大的挑战,同时也决定了水声信道是一种时频双扩展信道,提出一种水声OFDM通信系统中基于软信息的迭代信道估计技术,利用基于复指数基扩展模型(CE-BEM)进行信道估计。OFDM系统本身可以消除由于多径引起的符号间干扰(ISI)。基于导频的BEM信道估计,可以实现对时变信道的估计,结合基于软信息迭代的迭代均衡模块,将每次迭代生成的符号软判决信息作为辅助导频用于信道估计。同时,为了防止由于信道时变引起的信道子载波间干扰(ICI)对导频符号的影响,采用基于保护间隔的导频插入法插入导频。仿真结果显示基于BEM的软信息迭代信道估计性能较非迭代信道估计时明显提升。 相似文献
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为研究工程区海域水沙特征的时空分布、运动规律,采用不同时期的现场水文泥沙资料,对射阳港拦门沙航道工程建设前后的水流、含沙量、悬沙粒径和底质特征进行了对比分析。研究表明:射阳港一期航道工程建设后航道内潮波发生变形,涨潮流速大、历时短;落潮流速小、历时长,进入到航道内泥沙很难被带出航道,容易导致航道淤积。工程区海域整体含沙量较大,一期工程建设后导堤内涨潮含沙量明显增大,口门净输沙向口内,通过口门进入到航道的高含沙水体是航道淤积的重要沙源之一。导堤间边滩表层存在部分淤泥,且具有一定流动性,在水流及自身重力作用下,边滩淤泥可归入航道内。 相似文献
12.
Estimation of Rapidly Time-Varying Sparse Channels 总被引：2，自引：0，他引：2
The estimation of sparse shallow-water acoustic communication channels and the impact of estimation performance on the equalization of phase coherent communication signals are investigated. Given sufficiently wide transmission bandwidth, the impulse response of the shallow-water acoustic channel is often sparse as the multipath arrivals become resolvable. In the presence of significant surface waves, the multipath arrivals associated with surface scattering fluctuate rapidly over time, in the sense that the complex gain, the arrival time, and the Dopplers of each arrival all change dynamically. A sparse channel estimation technique is developed based on the delay-Doppler-spread function representation of the channel. The delay-Doppler-spread function may be considered as a first-order approximation to the rapidly time-varying channel in which each channel component is associated with Doppler shifts that are assumed constant over an averaging interval. The sparse structure of the delay-Doppler-spread function is then exploited by sequentially choosing the dominant components that minimize a least squares error. The advantage of this approach is that it captures both the channel structure as well as its dynamics without the need of explicit dynamic channel modeling. As the symbols are populated with the sample Dopplers, the increase in complexity depends on the channel Doppler spread and can be significant for a severely Doppler-spread channel. Comparison is made between nonsparse recursive least squares (RLS) channel estimation, sparse channel impulse response estimation, and estimation using the proposed approach. The results are demonstrated using experimental data. In training mode, the proposed approach shows a 3-dB reduction in signal prediction error. In decision-directed mode, it improves significantly the robustness of the performance of the channel-estimate-based equalizer against rapid channel fluctuations. 相似文献
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开敞式航道粉砂骤淤的随机分析 总被引：3，自引：2，他引：3
沧州港建成投产以来,其开敞式航道在大风作用下常常发生严重的骤淤现象。文中以能量平衡为基础,建立计算粉砂骤淤的经验公式。通过近期实测骤淤量数据,率定公式中的待定参数。根据1979~2003年期间的大风观测数据,后报得到每年最大风况产生的开敞式航道的粉砂骤淤量。比较选择多种单因素极值统计模式,对年最大粉砂骤淤量序列进行长期统计预测,估计骤淤量的重现值,为港口航道的防淤减淤工程提供必要的技术参数。 相似文献
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Underwater acoustic transient signals are generated mechanically at known positions along a wharf. These signals are received by a wide aperture planar array of four underwater acoustic sensors, whose positions relative to the wharf are unknown. A method is described that enables the positions of the sensors to be estimated from accurate differential time-of-arrival measurements (with 0.1 /spl mu/s precision) as the signal wavefronts traverse the array. A comparison of the estimated positions with the nominal positions of the first three sensors, which form a 20-m-wide aperture horizontal line array, reveals a 2-cm displacement of the middle sensor from the line array axis. This slight bowing of the line array results in overranging (bias error of 3%) when the wavefront curvature method is used with the nominal collinear sensor positions to locate a static source of active sonar transmissions at a range of 59.2 m. The use of the spherical intersection method coupled with the estimated sensor positions of the line array provides an order of magnitude improvement in the range estimate (within 0.3% of the actual value). However, systematic ranging errors are observed when the sound propagation medium becomes nonstationary. Next, the differences in the arrival times of the direct path and boundary-reflected path signals at the middle sensor of the wide aperture line array are estimated using the differential phase residue of the analytic signal at the sensor output. These multipath delays are used to estimate the range and depth of the source. Although the average value of the multipath range estimates is within 0.5% of the actual value, the variance of the range estimates is 50 times larger when compared with the results of the spherical intersection and wavefront curvature methods. The multipath delay data are also processed to provide a reliable estimate of the temporal variation in the water depth enabling the tidal variation to be observed. 相似文献
16.
Bjerrum-Niese C. Bjorno L. Pinto M.A. Quellec B. 《Oceanic Engineering, IEEE Journal of》1996,21(2):143-149
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 相似文献
17.
厦门嵩屿附近水域洪水期悬浮泥沙活动的特征 总被引：2，自引：1，他引：2
本文根据1984～1986年5次水文泥沙观测资料,研究了福建厦门嵩屿附近水域洪水期悬浮泥沙对河口三角洲和厦门西港东渡以南海域的淤积作用。 相似文献
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健跳港是一个狭长的淤泥质港汊,针对枯季和洪季健跳港海床不同的冲淤特点,利用一维潮流泥沙模型复演了该港海床的冲淤过程,通过调整挟沙力系数来模拟健跳港枯水期的淤积和洪水期的冲刷这两种不同的海床变化形态,并预测了健跳港上游引水后对该港河床的淤积影响。 相似文献
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V. G. Perepelkin S. N. Kulichkov I. P. Chunchuzov R. D. Kuznetsov 《Izvestiya Atmospheric and Oceanic Physics》2011,47(1):1-14
Using the phenomenon of the partial reflection of acoustic waves from anisotropic wind-velocity and temperature inhomogeneities in the lower troposphere is justified in determining the structure of these inhomogeneities. The data (obtained with the method of bistatic acoustic sounding) on signals reflected from stratified inhomogeneities in the lower 600-m layer of the troposphere are given. A detonation-type pulsed acoustic source was used. The methods of isolating a small (in amplitude) reflected signal against the background of noise and determining the reflecting-layer height and the partial-reflection coefficient from the measured parameters (time delay and amplitude) of a reflected signal are presented. The method of estimating the vertical gradients of the effective sound speed and the squared acoustic refractive index from the partial-reflection coefficient previously calculated is described on the basis of an Epstein transition-layer model. The indicated parameters are experimentally estimated for concrete cases of recording reflected signals. A comparison of our estimates with independent analogous data simultaneously obtained for the same parameters with monitoring instruments (a sodar and a temperature profiler) has yielded satisfactory results. 相似文献