共查询到20条相似文献，搜索用时 15 毫秒
1.
The problem of rapid environmental assessment in a range-dependent environment is addressed. For rapid assessment, the exact geoacoustic parameters are not required, nor is it a requirement that the exact structure of the acoustic field (location of peaks and s) be matched by an acoustic prediction model. The parameters that are relevant are the overall transmission loss (incoherent TL), the time spread (/spl tau/), and the slopes of the range/frequency interference patterns (/spl beta/, the waveguide invariant). The rapid geoacoustic characterization algorithm uses a homogeneous single-sediment layer overlying a hard acoustic basement model to optimally match the predicted acoustic observables with those estimated from data. The approach is presented here and is applied to the range-dependent benchmark cases TC1 and TC2 from the Inversion Techniques Workshop held in Gulfport, MS, in May 2001. The technique successfully reproduces the acoustic observables and estimates the sediment sound-speed, density, and attenuation profiles, as well as the sediment thickness. 相似文献
2.
I. P. Chunchuzov S. N. Kulichkov O. E. Popov V. G. Perepelkin 《Izvestiya Atmospheric and Oceanic Physics》2010,46(5):597-607
A wave theory of propagation of an acoustic pulse in a moving stratified atmospheric layer above the ground with a finite
impedance of an underlying ground surface is developed. The shapes of acoustic signals in a near-ground atmospheric waveguide,
which are formed due to temperature inversion and a vertical shear of the wind velocity, are calculated based on this theory.
These signals are compared with those measured during the experiments where vertical profiles of the wind velocity and temperature
in an atmospheric boundary layer have been continuously controlled using a sodar, a temperature profile meter, and acoustic
anemometers or thermometers mounted on a 56-meter-high mast. The joint action of a near-ground acoustic waveguide, the impedance
of the underlying surface, and a vertical layered structure of the boundary atmospheric layer on a signal shape far from the
acoustic source are studied. 相似文献
3.
Peter G. Simpkin 《Marine Geophysical Researches》2005,26(2-4):171-181
Technical specifications for small seismic sound sources used in seismic profilers may provide details of the pressure signatures
as measured on the primary acoustic axis and in the far field but will rarely provide information regarding off-axis emission
or of the form of the signatures in the near field. Since shallow water geophysical mapping is now attracting more attention
in research establishments and in the commercial sector, off-axis information could become an important issue. The use of
a wide angle seismic configuration on a small scale will demand that directional source information be included in data processing
activities if the full potential of the data is to be realised. Direct measurement of the full near and far field characteristics
of a source are often not practical, however modelling of the acoustic field may offer a tractable alternative and a means
of rapidly generating source functions appropriate for advanced data processing. One such modelling approach reviewed here
uses a time domain method to synthesise off-axis signatures using a far field, on-axis reference signature. 相似文献
4.
A computational case study of coupled-mode 400-Hz acoustic propagation over the distance 27 km on the continental shelf is presented. The mode coupling reported here is caused by lateral gradients of sound-speed within packets of nonlinear internal waves, often referred to as solitary wave packets. In a waveguide having unequal attenuation of modes, directional exchange of energy between low- and high-loss modes, via mode coupling, can become time dependent by the movement of waves and can cause temporally variable loss of acoustic energy into the bottom. Here, that bottom interaction effect is shown to be sensitive to stratification conditions, which determine waveguide properties and, in turn, determine modal attenuation coefficients. In particular, time-dependent energy loss due to the presence of moving internal wave packets is compared for waveguides with and without a frontal feature similar to that found at the shelfbreak south of New England. The mean and variability of acoustic energy level 27 km distant from a source are shown to be altered in a first order way by the presence of the frontal feature. The effects of the front are also shown to be functions of source depth. 相似文献
5.
《Oceanic Engineering, IEEE Journal of》2006,31(2):384-401
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. 相似文献
6.
南海北部陆坡海域是孤立内波的活跃区,孤立内波在该海域能够引起水体环境较强烈的水平不均匀性,从而影响声场干涉结构。将描述宽带声信号强度干涉条纹斜率的波导不变量视为一种分布,能更准确地分析声场的距离*频率干涉结构。本文研究了孤立内波环境下过渡海域声场的距离*频率干涉结构,依据实测孤立内波海洋环境,得到孤立内波环境下随距离变化的声速剖面,利用抛物方程方法仿真过渡海域声场干涉结构。在此基础上,利用拉东变换和傅里叶变换结合的谱值分离方法在低信噪比环境下提取波导不变量分布。分析表明孤立内波环境下过渡海域的声场类影区、类会聚区的波导不变量取值更丰富。 相似文献
7.
低盐透镜现象是珠江口陆架海域常见的一种中尺度现象,它的出现会影响水下声传播环境。利用南海北部陆架区的CTD资料分析了低盐透镜的结构特征,基于简正波和射线模型,建立二维波导环境,设置不同声源条件,对低盐透镜环境的声传播特性进行了研究。结果表明:低盐透镜会在海水上层形成声道,距离15 km处其传播损失较没有低盐透镜的情况小约15 dB。虽然低盐透镜声道厚度通常较小,但是较大的盐度梯度可以保证声道对声能的有效传播。当频率高于截止频率的声源置于低盐透镜内,声道效应有助于声音的远距离传播。 相似文献
8.
A model-based approach to solve a deep water ocean acoustic signal processing problem based on a state-space representation of the normal-mode propagation model is developed. The design of a model-based processor (MBP) for signal enhancement employing an array consisting of a large number of sensors for a deep ocean surveillance operation is discussed. The processor provides enhanced estimates of the measured pressure-field, modes, and residual (innovations) sequence indicating the performance or adequacy of the propagation model relative to the data. It is shown that due to the structure of the normal-mode model the state-space propagator is not only feasible for this large scale problem, but in fact, can be implemented by a set of decoupled parallel second-order processors, implying a real-time capability. In the paper we discuss the design and application of the processor to a realistic set of simulated pressure-field data developed from a set of experiments and sound speed parameters 相似文献
9.
10.
应用WOA13季节平均数据和BELLHOP模型,在季节、声源频率等因素确定的情况下,分10 m表面声源和250 m水下声源,分析北大西洋冬季东、西部海区的声波导情况。在给出不同海区位置的声速场和声波导具体信息的基础上,研究其规律:最小声速值和声道轴深度由直布罗陀海峡向外递减扩散,表层声速值和声速梯度由南向北递减,声跃层存在于低纬度海区,混合层在低纬度通常在100 m以内,在高纬度增加至100 m以上。10 m深度表面声源的汇聚区反转深度随纬度增加逐渐减少,西部海区深于东部海区;西部海区的汇聚区跨度大于东部海区,东西部跨度最大值出现在25°N和15°N,传播损失基本一致。250 m水下声源的汇聚区反转深度浅于10 m深度表面声源时,同样是西部海区大于东部海区,汇聚区跨度呈低-高-低规律,东西部跨度最大值出现在35°N和25°N;东部海区25°N以南、西部海区15°N以南,不同接收深度上的传播损失差异较大,以北差异较小。同时简要叙述了声影区对目标探测的影响。 相似文献
11.
Lynch J.F. Newhall A.E. Sperry B. Gawarkiewicz G. Fredricks A. Tyack P. Chiu C.S. Abbot P. 《Oceanic Engineering, IEEE Journal of》2003,28(1):129-150
The spatial and temporal variability of the acoustic field in the region of a strong coastal shelfbreak front are examined, using the high-resolution environmental data from the 1996-1997 New England shelfbreak PRIMER experiment to provide input to acoustic propagation models. Specifically, the "SeaSoar" undulating conductivity-temperature-depth (CTD) probe across-shelf transects provide 1-km along-track resolution, including the front, during the spring, summer, and winter seasons. These data allow one to study the diurnal and seasonal temporal variation of the acoustic field, as well as the varying spatial structure of the field. Using the RAM parabolic equation code, across-shelf acoustic field structure at 200, 400, and 1000 Hz is studied for various source depths. A number of interesting propagation effects are noted, the most interesting of which are the inhibition of strong acoustic-bottom interaction by the warm shelf water beneath the shelfbreak front and the existence of small-scale ducts near the front, due to offshore transport. Data from the vertical line arrays deployed as part of PRIMER offer partial validation of the predictions made. Specifically, it is seen that the mean received levels are in reasonable accord with propagation calculations made using locally measured bottom properties and the SeaSoar water-column measurements. 相似文献
12.
Experimental investigation of the combustive sound source 总被引：3，自引：0，他引：3
In this paper, we describe a unique low frequency underwater sound source called the combustive sound source (CSS). In this device, a combustible gas mixture is captured in a combustion chamber and ignited with a spark. The ensuing combustion produces expanding gases which in turn produce high intensity, low frequency acoustic pulses. With high-speed motion pictures of the CSS event, we relate the motion of the bubble to the acoustic waveform. We also compare the measured first bubble period in the CSS pressure signature with the predictions of the Rayleigh-Willis equation, including the dependence of the radiated acoustic waveform on the volume and depth of the bubble. Measurements of the first bubble period agree with Rayleigh-Willis theory in trend, but not in absolute value. In addition, we discuss the variation of the acoustic output with the fuel/oxygen mixture. Finally, several other factors that affect the acoustic output of CSS are discussed. These include the shape of the CSS combustion chamber, the type of oxidizer and fuel, and the ignition source 相似文献
13.
《Oceanic Engineering, IEEE Journal of》2009,34(1):12-23
14.
Acoustic wave fields in an ocean waveguide with a sediment layer having continuously varying density and sound speed overlying an elastic subbottom are considered in this analysis. The objective of this study is to investigate the effects of seabed acoustic properties, including the density and sound speed of the sediment layer and subbottom, on the characteristics of the wave fields. Examination of the reflection coefficient, wavenumber spectrum, and noise intensity of the sound field through numerical analysis has shown that the variation in the acoustic properties in the sediment layer is an important factor in determining the reflected or noise sound fields. In particular, the sediment thickness-to-wavelength ratio and the types of variation of acoustic properties inside the layer give rise to many characteristics that potentially allow for acoustic inversion of the seabed properties. With regard to the wave-field components in a shallow-water environment, the various types of waves existing in a seismo-acoustic waveguide have been illustrated. The results indicate that the effects of the sediment properties on the wavenumber spectrum are primarily on the continuous and evanescent regimes of the wave field. The noise intensity generated by distributive random monopoles at various depths, together with the effect of refractive sound-speed distribution in the water column, has been obtained and analyzed. 相似文献
15.
16.
Underwater acoustic communications (UAC) at the reverberation-limited range results in severely distorted information signals. Wide-band signals are subject to both intermodal and intramodal-type of dispersions. The underwater acoustic channel impulse response and the sidelobes strongly depend on the waveguide structure and the source and receiver positions. The motion and displacement from this position, as well as other environmental variabilities impose a real-time adaptivity for the receiver operation to keep track of the fluctuations. To increase the system's reliability and data rate, there is a need to employ adaptive equalizers and diversity techniques to improve the margins against noise, and intersymbol interference (ISI). Blind adaptive equalization (BAE) is the ideal adaptive compensation when operating point-to-multipoint networks, and centralized communication systems in general. Inherent optimum multiple resonant modes within the ocean acoustic waveguide can be exploited judiciously via a new proposed parallel data multicarrier modulation (MCM) scheme by sending data over the multiple subcarriers. MCM might eventually obviate equalization which introduces higher-order computational complexity to the receiver. The above modulation eliminates multipaths and allows operation at multiples of the single-carrier transmission rate. The system's immunity to distortions such as ISI, fast fades, and impulsive noises, is increased due to incorporation of symbol guard space. Direct comparisons with single carrier schemes (such as higher-order statistics (HOS)-based equalization) are of great interest, since the proposed new receiver configuration has low-complexity to provide a compact, portable and low-power practical acoustic modem. Finally, network topology issues are considered to determine optimum network architectures for underwater acoustic LANs. A central topology (CT) supported by BAE and MCM transmission is proposed 相似文献
17.
《Oceanic Engineering, IEEE Journal of》2006,31(2):325-344
Matched-field methods concern estimation of source locations and/or ocean environmental parameters by exploiting full wave modeling of acoustic waveguide propagation. Typical estimation performance demonstrates two fundamental limitations. First, sidelobe ambiguities dominate the estimation at low signal-to-noise ratio (SNR), leading to a threshold performance behavior. Second, most matched-field algorithms show a strong sensitivity to environmental/system mismatch, introducing biased estimates at high SNR. In this paper, some theoretical developments on matched-field performance analysis are summarized, including Bayesian performance bounds and probabilistic ambiguity analysis, both incorporating environmental/system uncertainty/mismatch. Performance analysis is then implemented for source localization in a typical shallow water environment chosen from the Shallow Water Evaluation Cell Experiments (SWellEX). The performance predictions describe the simulations of the maximum-likelihood estimator (MLE) well, including the mean-square error (MSE) in all SNR regions as well as the bias at high SNR. The threshold SNR and bias predictions are also validated through SWellEX experimental data processing. The results suggest the current environmental, acoustic, and statistical modeling has developed to such a level that the optimum theoretical matched-field performance can be achieved in a well-controlled experiment. 相似文献
18.
Diamicton-dominated shelf glacigenic sequences are characterized on high-resolution seismic records by a structureless to chaotic acoustic texture, often with abundant hyperbolic (point-source) reflections. Existing depositional models, based primarily on seismic data, have been constructed on the basis that this acoustic signature is indicative of subglacial till. However, borehole data from the UK continental shelf indicate that glaciomarine facies are also present. Thus, while this acoustic character may be indicative of diamicton lithofacies, it should not be taken as a predictive genetic indicator of a specific depositional process. 相似文献
19.
重物在落水和着底过程中都会产生瞬态声信号,这类信号可被运用于浅水区域水下目标定位。 针对浅水区域目标定位的问题,提出了一种基于小型立体五元基阵的瞬态声源快速被动定位算法。 在分析重物落水信号特征的基础上,选取合适的广义互相关加权函数求得传声器之间的声程差,运用快速最小二乘搜索算法进行声源定位。 结果表明:运用 5 传声器阵列可以同时兼顾定位精度和鲁棒性,且满足实时性要求,该方法可运用于浅水区域瞬态声源定位等领域。 相似文献
20.
The construction of stationary expressions for quantities of physical interest such as radiated power and target strength is discussed broadly for acoustic problems involving radiation or scattering from finite objects of arbitrary shape. The Kirchhoff-Helmholtz integral corollaries of the wave equation, which express acoustic pressure at either interior or exterior points in terms of pressure and its normal derivative over any closed surface, yield for both interior and exterior problems two mathematically dissimilar but related functional relations between surface field quantities. One of these is the better known surface Helmholtz integral equation; the other is a differential-integral relation which involves the tangential derivatives of pressure on the surface. The four linear operators involved in these functional relations are studied and it is found that two are self-adjoint, while the other two are an adjoint pair. A general technique for constructing variational expressions recently developed by Gerjuoy et al. [28] is adapted to acoustic radiation and scattering problems with the functional relations taken as the primary governing relations. Included examples are stationary expressions for the radiated power when either the normal velocity or the pressure are specified on the surface (the other quantity being unknown) and the target strength for scattering from a rigid object. The adjoint relations allow simple physical interpretations for the Lagrange multipliers that arise in the theory, such that the guesses for good trial functions can take advantage of existing physical insight. It is demonstrated with a specific example (transversely vibrating disk) that the resulting estimate for radiated power is substantially more accurate than that of the trial function for surface pressure which was inserted into the stationary expression. 相似文献