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。     

Physical modeling of long-range infrasonic propagation in the atmosphere

The results of experiments on the physical modeling of long-range infrasonic propagation in the atmosphere are given. Such modeling is based on the possible coincidence between the forms of the vertical profiles of the effective sound speed stratification in the atmospheric boundary layer (between 0 and 600 m for the case under consideration) and in the atmosphere as a whole (from the land surface up to thermospheric heights (about 150 km)). The source of acoustic pulses was an oscillator of detonation type. Owing to the detonation of a gas mixture of air (or oxygen) and propane, this generator was capable of producing short, powerful (the maximum acoustic pressure was on the order of 30 to 60 Pa at a distance of 50 to 100 m from the oscillator), and sufficiently stable acoustic pulses with a spectral maximum at frequencies of 40 to 60 Hz and a pulsing period of 20 to 30 s. The sites of acoustic-signal recording were located at different distances (up to 6.5 km) from the source and in different azimuthal directions. The temperature and wind stratifications were monitored in real time during the experiments with an acoustic locator—a sodar—and a temperature profiler. The data on the physical modeling of long-range sound propagation in the atmosphere are analyzed to verify the physical and mathematical models of predicting acoustic fields in the inhomogeneous moving atmosphere on the basis of the parabolic equation and the method of normal waves. A satisfactory agreement between calculated and experimental data is obtained. One more task was to compare the theoretical relations between variations in the azimuths and angles of tilting of sound rays about the horizon and the parameters of anisotropic turbulence in the lower troposphere and stratosphere with the experimental data. A theoretical interpretation of the experimental results is proposed on the basis of the theory of anisotropic turbulence in the atmosphere. The theoretical and experimental results are compared, and a satisfactory agreement between these results is noted.     

Effects of Korean littoral environment on acoustic propagation

Environmental acoustics experiments were recently conducted in shallow to intermediate water depths in the Sea of Japan, east of Korea, along the shelf and slope, covering frequencies from 25 to 800 Hz. These were operational experiments carried out in three different seasons. The primary objectives of the data reported here are: (1) to characterize the Korean coastal environment during May 1998, September 1998, and February 1999 and (2) to assess how complexities of the environment might impact acoustic propagation in May and February, as measured by its transmission loss. Propagation data were obtained from broadband explosive SUS sources and sonobuoy receivers. The tests were conducted over varying bottom depths and slopes, both approximately normal and parallel to the bathymetric contours. Two different source depths were included. Environmental and acoustic data are reviewed and discussed. While many aspects of the observed propagation remain ill understood, on the whole a consistent and useful picture has emerged of acoustic propagation in this region. Environmental impacts on propagation are associated mainly with bottom properties, somewhat less so with source depth in relationship to sound speed profiles, and almost not at all with range-dependent profiles of a water mass front     

Effect of the Internal Tide on Acoustic Transmission Loss at Midfrequencies

Nonlinear internal waves are a common event on the continental shelf. The waves depress the high-gradient region of the thermocline and thicken the surface mixed layer with consequent effect on acoustic propagation. After the waves have passed, it may take several hours for the thermocline to rise to its prewave level. To examine the effect of the rising thermocline, oceanographic and acoustic data collected during the 2006 Shallow Water Experiment (SW06) are analyzed. Midfrequency acoustic data (1.5–10.5 kHz) taken for several hours at both fixed range (550 m) and along a tow track (0.1–8.1 km) are studied. At the fixed range, the rising thermocline is shown to increase acoustic intensity by approximately 5 dB . Along the tow track, the transmission loss changes 2 dB for a source–receiver pair that straddles the thermocline. Using oceanographic moorings up to 2.2 km away from the acoustic receiver, a model for the rising thermocline is developed. This ocean model is used as input to a broadband acoustic model. Results from the combined model are shown to be in good agreement with experimental observation. The effects on acoustic signals are shown to be observable, significant, and predictable.      

LOAPEX: The Long-Range Ocean Acoustic Propagation EXperiment

This paper provides an overview of the experimental goals and methods of the Long-range Ocean Acoustic Propagation EXperiment (LOAPEX), which took place in the northeast Pacific Ocean between September 10, 2004 and October 10, 2004. This experiment was designed to address a number of unresolved issues in long-range, deep-water acoustic propagation including the effect of ocean fluctuations such as internal waves on acoustic signal coherence, and the scattering of low-frequency sound, in particular, scattering into the deep acoustic shadow zone. Broadband acoustic transmissions centered near 75 Hz were made from various depths to a pair of vertical hydrophone arrays covering 3500 m of the water column, and to several bottom-mounted horizontal line arrays distributed throughout the northeast Pacific Ocean Basin. Path lengths varied from 50 km to several megameters. Beamformed receptions on the horizontal arrays contained 10–20-ms tidal signals, in agreement with a tidal model. Fifteen consecutive receptions on one of the vertical line arrays with a source range of 3200 km showed the potential for incoherent averaging. Finally, shadow zone receptions were observed on an ocean bottom seismometer at a depth of 5000 m from a source at 3200–250-km range.      

Long-term measurement of temperature variabilities off Mindanao Island by the ocean acoustic tomography

Oceanic variabilities off Mindanao Island, Philippines where the North Equatorial Current branches into the Kuroshio and the Mindanao Current were measurerd for a period from 14 Feb.–1 Jun. 1992 by the oceean acoustic tomography (OAT). From the beginning of April, the travel time of acoustic rays propagating over a horizontal distance of about 250km, through the depth range of 80–4700 m around the underwater sound channel began to decrease, implying a warming of water. This variability was also confirmed with the results of temperature measurement at the sites where a sound source and receiver were located. The TOGA/TAO array data show that the OAT experiment was done when the 1991–1992 El Nino was at a decaying stage and the resulting warming-up of water occurred at the western Pacific. This study provides us a first evidence of ENSO-related variabilities detected by the OAT.     

Seasonal variations of sound speed in the Arabian Gulf

Sound-speed computations from CTD casts in the Arabian Gulf during 1992, reveal spatial and temporal variations in acoustic properties. Hydrographic conditions affecting sound speed propagation were seasonally investigated. A monotonic decrease in sound speed profiles with depth was commonly observed at almost all the stations in the Gulf. However, an exception occurred at Hormuz strait during winter. The water exchange pattern between the Gulf of Oman and the Arabian Gulf seems to influence the sound-speed structure, especially in the southern part of the latter. Winter profiles along the Gulf axis showed almost vertically homogenous sound speed. Maximum speeds are observed in summer, with a strong gradient associated with the development of the summer thermocline layer. Horizontal distributions in both winter and summer show a decreasing trend in sound speed from the Strait of Hormuz to the head of the Gulf. The resultant profiles provide a more comprehensive and reliable data set than any that have been reported in the literature. Shallowness and multiple refraction and reflection in the Arabian Gulf may cause sound speed energy to be trapped. No sound channel was detected inside the Gulf. A correlation analysis shows that sound speed is closely correlated with temperature throughout the Gulf, except in winter in the southern half where salinity effects, as a result of inversion and water exchange at the entrance, are found to be dominant.     

Ocean acoustic tomography as a data assimilation problem

The ocean acoustic tomographic (OAT) approach to sound speed field estimation is generalized to include a variety of sources of information of interest such as an oceanographic model of the sound speed field, direct local sound speed measurements, and a full field acoustic propagation model as well as measurements. The inverse problem is presented as a four-dimensional field estimation problem using a variational approach commonly used in oceanographic data assimilation. The current OAT approach is shown to be a special case of the general framework. The matched-field tomography (MFT) approach is also discussed within this context. A simple implementation of this novel approach is then investigated in the absence of a suitable oceanographic model, and acoustic propagation is accounted for using a standard parabolic equation model. The inverse equations derived are validated numerically through a simple inversion example, and some issues on environmental mismatch and computations are discussed. The developments then provide a basic framework for ongoing data-model melding in acoustically focused oceanographic sampling (AFOS) network     

季节因素对大西洋声传播的影响分析

以分析季节对大西洋声传播的影响为研究目的,应用WOA13季节平均数据和Mackenzie声速经验公式,分析了大西洋声道轴和表层声速值的四季分布情况,再利用BELLHOP水声学数值模型,在设定的声源频率1 000 Hz和掠射角15°～-15°情况下,仿真计算选用位置点5 m深度声源的四季声传播情况,研究结果表明:按照实际的季节,大西洋会聚区波导的反转深度,冬季最小,春季增大,夏季最大,秋季再减小.在中低纬度的典型声速剖面下,夏季会聚区跨度最大,秋季和冬季递减,春季最小,第一会聚区的四季跨度差在1 km内.在高纬度的正梯度声速剖面下,夏季声传播距离最远,秋季减小,冬季最近,春季增大,且传播距离的差别较大.各变化规律均以四季循环更替的形式出现.     

A modeling study of acoustic propagation through movingshallow-water solitary wave packets

Propagation of 400-Hz sound through continental-shelf internal solitary wave packets is shown by numerical simulation to be strongly influenced by coupling of normal modes. Coupling in a packet is controlled by the mode coefficients at the point where sound enters the packet, the dimensions of the waves and packet, and the ambient depth structures of temperature and salinity. In the case of a moving packet, changes of phases of the incident modes with respect to each other dominate over the other factors, altering the coupling over time and thus inducing signal fluctuations. The phasing within a moving packet varies with time scales of minutes, causing coupling and signal fluctuations with comparable time scales. The directionality of energy flux between high-order acoustic modes and (less attenuated) low-order modes determines a gain factor for long-range propagation. A significant finding is that energy flux toward low-order modes through the effect of a packet near a source favoring high-order modes will give net amplification at distant ranges. Conversely, a packet far from a source sends energy into otherwise quiet higher modes. The intermittency of the coupling and of high-mode attenuation via bottom interaction means that signal energy fluctuations and modal diversity fluctuations at a distant receiver are complementary, with energy fluctuations suggesting a source-region packet and mode fluctuations suggesting a receiver-region packet. Simulations entailing 33-km propagation are used in the analyses, imitating the SWARM experiment geometry, allowing comparison with observations     

PAssive COastal TOMography: an Innovative Approach for the Remote Monitoring of Sea Temperature

Abstract. This paper describes a new Ocean Acoustic Tomography (OAT) methodology - a passive tomography - presently in an advanced development phase. This technique has been developed for long-term, extensive, remote monitoring of the seawater temperature spatial distribution, which is estimated from the received noise emitted from ships of opportunity. To test the passive tomographic processor under controlled conditions, the components of the naval noise from different kinds of vessels was analysed and realistic naval noise was simulated. The feasibility of the proposed methodology was confirmed by test-runs on semi-synthetic data; its capability to resolve temperature profiles will be better assessed with the use of real acoustic and environmental data collected during the INTIMATE00 experiment performed in October 2000 in the Atlantic Ocean off the Portuguese coast. An analysis of the space and time variability of the Empirical Orthogonal Function (EOF) decomposition of the sound speed (SSP) in the Mediterranean Sea has been carried out to identify areas where acoustic tomography can be successfully applied. Results from simulations in the South Adriatic Sea, which was identified as a region with a high sound speed variability associated with the seasonal cycle and with the main oceanographic processes, are reported.     

Kraken海洋声学模型及其声传播与衰减的数值试验

针对射线、简正波、PE、FFP等传播模型的算法原理及其适用的海洋环境,建立了以Kraken声学模型计算软件为基础的海洋声场数值预报系统.应用该预报系统对4组典型的海洋声场进行了数值试验,结果表明:在相同的海面和海底边界条件下,声场分布是由声速剖面和声源位置决定的.在负梯度声场中,所有声线都折向海底,在极限声线外产生阴影区.声源位于声道轴附近的温跃层中会产生波导传播.用射线理论解释了上述现象的成因,指出了其实际应用价值.     

Refraction of Sound in a Horizontally Inhomogeneous, Time-Dependent Ocean

Measurements of the three-dimensional (3-D) structure of a sound-speed field in the ocean with the spatial and temporal resolution required for prediction of acoustic fields are extremely demanding in terms of experimental assets, and they are rarely available in practice. In this study, a simple analytic technique is developed within the ray approximation to quantify the uncertainty in acoustic travel time and propagation direction that results from an incomplete knowledge or purely statistical characterization of sound-speed variability in the horizontal plane. Variation of frequency of an acoustic wave emitted by a narrowband source due to a temporal variation of environmental parameters is considered for deterministic and random media. In a random medium with locally statistically homogeneous, time-dependent 3-D fluctuations of the sound speed, calculation of the signal frequency and bearing angle variances as well as the travel-time bias due to horizontal refraction is approximately reduced to integration of respective statistical parameters of the environmental fluctuations along a ray in a background, range-dependent, deterministic medium. The technique is applied to acoustic transmissions in a coastal ocean, where tidally generated nonlinear internal waves are the prevailing source of sound-speed fluctuations, and in a deep ocean, where the fluctuations are primarily due to spatially diffuse internal waves with the Garrett–Munk spectrum. The significance of 3-D and four-dimensional (4-D) acoustic effects in deep and shallow water is discussed.     

Specific Features of the Influence of the Lower Boundary of a Waveguide on the Angular Structure of the Sound Field in the Shelf Zones in the Northwest Part of the Black Sea

We analyze the possibility of existence of critical angles of incidence of sound waves along two paths of propagation of sound typical of the northwest shelf of the Black Sea from the viewpoint of the characteristics of the lower boundary of a waveguide and the space and time structure of the field of sound velocity. The lower boundary of the waveguide may possess the property of acoustic transparency both in the case of a subsurface sound channel and under the conditions of negative refraction if the bottom is formed by fine-aleurite silts responsible for significant losses in the process of propagation of sound. The angles of total internal reflection exist for bottoms formed by shell rocks under all hydrological conditions typical of this region. At the same time, for bottoms formed by fine-aleurite silts, these angles exist only for a certain vertical structure of the field of sound velocity, which enables one to use the range of angles in which the losses caused by the reflections of sound waves from the bottom can be neglected.     

海洋声速剖面的自动聚类研究

以海区30'网格方区多年月平均统计的声速剖面作为原始数据集,提取声速剖面的表层、主跃层和深海等温层分层结构特征,把我国近海及其邻近海域预分为Ⅰ,Ⅱ和Ⅲ类区。对Ⅱ,Ⅲ类区声速剖面,应用有序样本聚类算法分别进行表层分离。根据各类区的表层声速剖面数据,通过归一化处理和Akima差值采样得到梯度剖面,建立起按月归一化后的声速剖面分层梯度样本集,并应用系统聚类法和SOFM神经网络方法分别进行聚类分析,再根据分类结果并结合各类型海区的声学特点,得到各类型海区声速剖面的典型类型。通过对大量历史数据的分析结果表明,该方法为自动分类海洋声速剖面提供了一条有效路径,弥补了长期以来海洋声速剖面主要依靠人工分类的不足。     

西北太平洋副热带模态水形成区声传播特性分析

利用Argo剖面数据和水声学数值模型,分析了西北太平洋副热带模态水(STMW)形成区因季节性环境差异所引起的水声传播变化特征。声场计算结果表明,STMW形成区域的声传播为近表层波导与会聚区的复合形式,其中会聚区终年存在,表面波导在秋、冬两季混合层加深的环境条件下出现,次表层波导在夏季STMW潜沉的环境条件下出现。上层海洋中两类不同形式的波导使表层和次表层的声能分布呈反相变化,波导内与波导外的声能差异可达10~15dB(声波频率为1 000Hz)。STMW的季节性变化还会引起会聚区的位置差异,具体情况与声源深度有关。声源在20m时,夏季会聚区距离最远,秋季、春季次之,冬季最近,夏季和冬季相差6.6km;声源在150m时,夏季会聚区距离缩短了3.1km,其他季节变化不大。     

Acoustic wave propagation in horizontally variable media

An overview of the multipath expansion method of solving the Helmholtz wave equation to describe the underwater sound field for a fixed point source in a plane multilayered medium is presented. The approach is then extended to account for horizontal variations in bottom depth, bottom type, and sound speed in the stationary phase approximation. Comparisons of model results to a limited number of measured data sets and standard propagation codes are presented.     

Characteristics of acoustic propagation to the eastern vertical line array receiver during the summer 1996 New England shelfbreak PRIMER experiment

During July and August of 1996, the summer component of the New England shelfbreak front PRIMER experiment was fielded in the Mid-Atlantic Bight, at a site due south of Martha's Vineyard, MA. This study produced acoustic transmission data from a network of moored sources and receivers in conjunction with very-high-resolution oceanography measurements. This paper analyzes receptions at the northeast array receiver from two 400 Hz acoustic tomography sources, with the transmission paths going from the continental slope onto the continental shelf. These data, along with forward acoustic-propagation modeling based on moored oceanographic data, SeaSoar hydrography measurements, and bottom measurements, reveal many new and interesting aspects of acoustic propagation in a complicated slope-shelf environment. For example, one sees that both the shelfbreak front and tidally generated soliton internal wave packets produce stronger mode coupling than previously expected, leading to an interesting time-and-range-variable population of the acoustic normal modes. Additionally, the arrival time wander and the signal spread of acoustic pulses show variability that can be attributed to the presence of a frontal meander and variability in the soliton field. These and other effects are discussed in this paper, with an emphasis on creating a strong connection between the environmental measurements and the acoustic field characteristics.     

Vertical distribution of the sound speed in the Gulf Stream system

Using archived historical data on the temperature/salinity distribution, this paper describes the structure of the mean seasonal and the actual field of the computed speed of sound in the Gulf Stream region. The formation of acoustic channels of large, medium, and small size is considered, depending on the vertical thermohaline structure of waters. The paper provides statistical characteristics of the sound speed field and acoustic channels of waters interacting in the Gulf Stream system. Translated by Vladimir A. Puchkin.