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1.
Acoustic backscattering experiments in a well characterized sand sediment: data/model comparisons using sediment fluid and Biot models 总被引：2，自引：0，他引：2
Williams K.L. Jackson D.R. Thorsos E.I. Dajun Tang Briggs K.B. 《Oceanic Engineering, IEEE Journal of》2002,27(3):376-387
As part of the sediment acoustics experiment 1999 (SAX99), backscattering from a sand sediment was measured in the 20- to 300-kHz range for incident grazing angles from 10/spl deg/ to 40/spl deg/. Measured backscattering strengths are compared to three different scattering models: a fluid model that uses the mass density of the sediment in determining backscattering, a poroelastic model based on Biot theory and an "effective density" fluid model derived from Biot theory. These comparisons rely heavily on the extensive environmental characterization carried out during SAX99. This environmental characterization is most complete at spatial scales relevant to acoustic frequencies from 20 to 50 kHz. Model/data comparisons lead to the conclusions that rough surface scattering is the dominant scattering mechanism in the 20-50-kHz frequency range and that the Biot and effective density fluid models are more accurate than the fluid model in predicting the measured scattering strengths. For 50-150 kHz, rough surface scattering strengths predicted by the Biot and effective density fluid models agree well with the data for grazing angles below the critical angle of the sediment (about 30/spl deg/) but above the critical angle the trends of the models and the data differ. At 300 kHz, data/model comparisons indicate that the dominant scattering mechanism may no longer be rough surface scattering. 相似文献
2.
To observe sound penetration into a sandy sediment, a buried acoustic receiving array was insonified by a wide band sound source carried by a remotely operated vehicle. A slanting array design was used to avoid scattering artifacts. This design overcame possible problems in previous experiments, in which scattering artifacts from the array structure could be mistaken for a propagating wave. The experiments took place in a sandy sediment off the West coast of Florida, as part of the sediment acoustics experiment, which is a multidisciplinary effort to study sediment acoustics. A coherent angle, speed, and height estimation process searched through a four-dimensional search space, of source height and elevation angle, wave speed, and propagation delay to find spherical acoustic wave fronts. Three main categories of waves were found: first refracted, dominant nonrefracted and evanescent. Later acoustic arrivals, a fourth category, remain to be analyzed. Their relative intensities effectively characterize the sediment penetrating acoustic energy. The acoustic sound pressure level of penetrating waves below the critical grazing angle was found to be greater than expected for a flat interface. 相似文献
3.
This paper applies a full-field technique to invert bottom sound profile and bottom reflectivity from simulated acoustic data in a shallow water environment. Bottom sound-speed profile and bottom reflectivity have been traditionally estimated using seismic reflection/refraction techniques when acoustic ray paths and travel time can be identified and measured from the data. However, in shallow water, the many multipaths due to bottom reflection/refraction make such identification and measurement rather difficult. A full-field inversion technique is presented here that uses a broad-band source and a vertical array for bottom sound-speed and reflectivity inversion. The technique is a modified matched field inversion technique referred to as matched beam processing. Matched beam processing uses conventional beamforming processing to transform the field data into the beam domain and correlate that with the replica field also in the beam domain. This allows the analysis to track the acoustic field as a function of incident/reflected angle and minimize contamination or mismatch due to sidelobe leakage 相似文献
4.
为厘清海底沉积层声学特性信息的水声环境保障需求,构建浅海两层海底环境参数模型,并参考Hamilton海底底质9种分类设置沉积层声速、密度、衰减系数及厚度的参考值及计算采样区间,利用Kraken简振波模型,采用控制变量的方法,研究了浅海沉积层声学特性参数对声传播损失的影响;开展了建模理论推导及数值技术分析,研究了海底沉积层声学特性参数在模型计算过程中调用过程,并从建模计算的角度对仿真计算的结果进行解释,对海底沉积层声学特性调查装备发展及调查重点参数具有一定的参考价值。 相似文献
5.
Acoustic backscattering from a sandy seabed was measured at a frequency of 5.5 kHz at a wide range of grazing angles. The measurement system used was the University of Miami's sonar tower, consisting of an omni-directional broadband source and two 16-channel hydrophone receiver arrays. A volume scattering model, which combines a fluid model with reflection/transmission coefficients derived from the Biot theory, is used. This model allows energy penetration into the bottom, calculations of the volume scattering at all grazing angles, and the frequency dependence of the sound speed in the water-saturated sediment. In the model, rather than assume sound-speed correlation length in sedimentary volume, core data were used to assimilate a 3-D fluctuation spectrum of the density. The numerical results showed excellent agreement with the measurement at lower grazing angles. We concluded that the interface roughness scattering was dominant at lower grazing angles, while the volume scattering is dominant at higher grazing angles at the sandy site. The border of the dominance of the interface and volume scattering was the so-called critical angle at this frequency. The frequency dependence of sound speeds is also discussed. 相似文献
6.
Estimation of Geoacoustic Properties of Marine Sediment Using a Hybrid Differential Evolution Inversion Method 总被引：1，自引：0，他引：1
《Oceanic Engineering, IEEE Journal of》2010,35(1):59-69
7.
Thorne P.D. Hardcastle P.J. Flatt D. Humphery J.D. 《Oceanic Engineering, IEEE Journal of》1994,19(1):48-57
Acoustics have the promise of being able to have a significant impact on our understanding of coastal sedimentary processes, which play such an important role in the dynamics of the coastal and shallow water environment. Due to this, the application of acoustics for remotely measuring suspended sediments, over ranges from metres to tens of metres, is gaining acceptance within the sediment community. This recognition of the use of acoustics to the area of sediment processes is based on advances which have been made decade in the understanding of the interaction of sound with marine suspended sediments, and also due to ongoing field observations which have shown the unique ability of the acoustic technique to measure suspended sediment profiles. In the present work acoustic measurements of suspended sediments have been conducted at 1, 2.5, 3, and 5 MHz in a number of different shallow water environments. The interpretation of the acoustic data to obtain suspended sediment concentration is presented, and some of the difficulties when inverting the acoustic information to obtain the suspended load are considered. Some discussion is also given to future uses of acoustics for studying sediment processes, and how one may utilize the application of underwater sound to manage our coastal environment more effectively 相似文献
8.
本文介绍在水深40—90米的浅海海域中三种类型沉积层海底上,用爆炸声源进行的海底反射损失的实验研究结果。实验结果与按均匀半空间底模型计算所得海底反射损失的理论曲线作了比较。结果表明:反射损失值明显地与底的类型有关,细砂底的反射损失较小,粉砂质泥次之,而粉砂质粘土的反射损失较大;对于同类型的海底,孔隙度大者反射损失也较大。此外,还讨论了沉积物中场速的两种经验公式的适用性。 相似文献
9.
关定华 《海洋学报(英文版)》1982,1(1):58-61
The sound field in shallow water is closely relatcd to the acoustic properties of thesea bottom which has complicated stratified structure. The influence of the bottom onthe sound field may be described in terms of reflection coefficient. In early papers, somesimplified dependence of the bottom reflection loss on the grazing angle has been sug-gested. But these models cannot reflect the main characteristics of angular dependenceof reflection loss in all cases. In this paper a simple approach to the problem is sug-gested. The sound field in homogeneous shallow water can be calculated for sea bottom,the reflection loss of which is arbitrarily monotonously increasing function of grazingangle. In this paper it is pointed out that there is a simple transformation between theangle dependence of bottom reflection loss and transmission ratio of sound field. 相似文献
10.
The major obstacle to underwater acoustic communication is the interference of multi-path signals due to surface and bottom reflections. High speed acoustic transmission over a shallow water channel characterized by small grazing angles presents formidable difficulties. The reflection losses associated with such small angles are low, causing large amplitudes in multi-path signals. In this paper we propose a simple but effective model for multi-path interference, which is then used to assess the performance of a digital communication system operating in a shallow water channel. The results indicate that transmission rates in excess of 8 kbits/s are possible over a distance of 13 km and channel depth of only 20 meters. Such a system offers improved performance in applications such as data collection from underwater sensors 相似文献
11.
为研究小尺度海底沉积物样品的声衰减特性,作者提出了用声学探针测量海底沉积物声波幅值的新方法,对沉积物样品扰动小,两个测量点的距离可小于波长,为海底沉积物微观声衰减测量提供了新手段。作者用小于波长的间隔逐点测量了沉积物的压缩波幅值,数据分析表明沿沉积物柱状样全长的声衰减满足指数衰减模型。目前主要用同轴差距衰减测量法获得海底沉积物声衰减数据,但该方法不能辨识声衰减模型,因此不同海区的测量结果难以建立联系。对此作者又提出用声吸收系数反演的幅值比与声衰减系数反演的R值(两种幅值比的比值)作评价依据,分析了垂直轴差距衰减测量法获得的南海海底沉积物声衰减测量数据,发现部分沉积物样品声衰减的R值远大于1,其声衰减不满足指数衰减模型。在声衰减满足指数衰减模型的条件下,用Hamilton的声衰减和频率经验公式预报的南海沉积物声衰减比与作者用声学探针测量海底沉积物所得的声衰减比对比,通过对R值分析得出Hamilton的声衰减和频率经验公式可以预报南海沉积物声衰减比的范围。作者提出的声学探针测量海底沉积物声衰减的方法的优点是既能获得声衰减数据又能辨识声衰减模型,不同海区测量的沉积物声衰减比可用R值建立联系。 相似文献
12.
Chotiros N.P. Mautner A.M. Lovik A. Kristensen A. Bergem O. 《Oceanic Engineering, IEEE Journal of》1997,22(4):604-615
An experiment was performed to measure sediment penetrating acoustic waves to test a model of acoustic propagation, which is based on Biot's theory. Independent geophysical measurements provided model input parameters. A parametric sound source was used to project a narrow beam pulse into a silty sand sediment at a shallow grazing angle. The sediment acoustic waves were measured by an array of buried sensors and processed to measure wave directions and speeds. Two acoustic waves were observed, corresponding to the fast and slow waves predicted by Biot's theory. Discrepancies between model predictions and measured acoustic waves were examined, deficiencies in the model identified, and strategies for improvement postulated. The permeability and bulk modulus of the solid frame were of particular interest 相似文献
13.
Rosa Freitas Leandro Sampaio Ana Maria Rodrigues Victor Quintino 《Estuarine, Coastal and Shelf Science》2005,65(4):625-632
An acoustic ground discrimination system (QTC VIEW, Series IV) was used to identify and map the bottom acoustic diversity in the bar channel of Ria de Aveiro, Western Portugal. The majority of the survey area presented shallow depth for this type of equipment, ranging mainly from 5 to 15 m. Depth occasionally reached 25 m in specific areas located across the entrance channel, dug by the strong tidal currents, reaching 3 m/s. The acoustic data were submitted to manual and auto-cluster and the results obtained from both procedures were coherent. Using aids to the acoustic classification and ground-truth sediment data, a final solution consisting of four acoustic classes was reached. Their geographical distribution was coincident with the spatial distribution of the major bottom types and sediment groups (hard bottom, coarse sand, medium sand and fine sand), identified through multivariate analysis of the grain-size data, and reflected the complex hydrodynamics of the entrance channel. The acoustic pattern was coincident at the intersections of the acoustic survey lines, assuring the repeatability of the acoustic procedure. Overall, the acoustic approach showed consistent results for the assessment and mapping of the benthic habitats in this shallow-water coastal area, providing a very valuable tool in an area where conventional sediment sampling is less favourable, namely due to strong tidal currents and frequent ship traffic, such as the entrance channel of Ria de Aveiro and the near-shore adjacent shelf. 相似文献
14.
Sunit K. Addy E. William Behrens Trent R. Haines Donald J. Shirley J. Lamar Worzel 《Marine Georesources & Geotechnology》2013,31(1):27-49
Abstract Eight types of reflections are interpreted from 3,800 km of 3.5 kHz profiles taken over a 25,000 km2 area of the upper continental slope and shelf in the northeastern Gulf of Mexico off Panama City, Florida. The corresponding sediments in five of the reflection types were sampled in 77 piston cores from which data were obtained on in situ acoustic velocities (V), bulk densities (gr), sediment texture (mean grain size = Mz), CaCO3 content (C), sedimentary structures, and gross sediment composition. A distinct bottom echo with numerous subbottom reflectors (Type I) is observed in deeper areas where terrigenous clay or lutite (Mgi = 9.9 to, gr = 1.4 g/cc, porosity (P) = 74 percent, C = 28 percent, and V (upper 2 m) = 1,435 m/s) predominates. Type I reflection grades upslope into Type IV, which shows a distinct bottom echo with fewer subbottom reflectors, and the corresponding sediment is a foraminiferal silty clay (mz = 9.4 to, gr = 1.43 g/cc, P = 73 percent, V = 1,447 m/s, and C = 37 percent). The uppermost slope gives indistinct, semiprolonged bottom echoes with faint subbottoms (Type VI) where calcareous silt (Mz = 6.6 to, gr = 1.57 g/cc, P = 65 percent, C = 70 percent, and V = 1,482 m/s) is the main sediment type. The shelf sediments (gr = 1.66 g/cc, P = 58 percent, V = sl1,530 m/ s), varying from coarse silt (Mz = 5.3 to) to very coarse sand (Mz = ‐0.3 to) and 25 to 100 percent carbonate, show indistinct, semiprolonged bottom echoes with intermittent or mushy subbottoms (Type VII). Prolonged echoes with no subbottoms (Type VIII) are observed in areas where algal sands of variable grain size (Mz ‐ ‐0.9 to 2.7 to, gr = 1.66 g/cc, P = 59 percent, V = 1,530 to 1,690 m/s) occur. The major trends in reflection types (loss in depth of penetration, loss in number of reflectors, and prolongation of initial bottom reflections) follow gradients of sedimentary and physical properties of the sediments, which are increases in mean grain size, bulk density, in situ acoustic velocity, CaCO3 content, and decrease in porosity. Increases in the reflection coefficient and attenuation of the sound energy in the shelf sediments are probably important factors in the observed decrease in the depth of penetration of the sound energy in the shelf sediments. 相似文献
15.
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
16.
在南黄海某一典型的砂质海底区域，采用全向性声源和全向性接收水听器开展了频率范围为6-24 kHz的海底反向声散射测量。测量结果表明，在避免海面散射干扰并满足远场条件的情况下，本次实验获得了掠射角范围为18~80°的海底反向声散射强度，其数值为-41.1~24.4 dB。在有效掠射角范围内，声散射强度总体上随掠射角的增大呈现出增大趋势，但对于不同的频率，其变化趋势有所不同，反映出不同的散射机理。在20°、40°和60°掠射角处，在6-24 kHz的频率范围内反向声散射强度总体上呈现出正相关的频率依赖性，其线性相关斜率分别为0.2229 dB/kHz、0.5130 dB/kHz、0.1746 dB/kHz。在最大掠射角80°处，反向声散射强度未呈现出明显的频率相关性。 相似文献
17.
Guanbao Li Jingqiang Wang Xiangmei Meng Baohua Liu Guangming Kan Guozhong Han Qingfeng Hua Yanliang Pei Lei Sun 《海洋学报(英文版)》2021,40(4):65-73
Building empirical equations is an effective way to link the acoustic and physical properties of sediments. These equations play an important role in the prediction of sediments sound speeds required in underwater acoustics.Although many empirical equations coupling acoustic and physical properties have been developed over the past few decades, further confirmation of their applicability by obtaining large amounts of data, especially for equations based on in situ acoustic measurement techniques, is required. A sediment acoustic survey in the South Yellow Sea from 2009 to 2010 revealed statistical relationships between the in situ sound speed and sediment physical properties. To improve the comparability of these relationships with existing empirical equations, the present study calculated the ratio of the in situ sediment sound speed to the bottom seawater sound speed, and established the relationships between the sound speed ratio and the mean grain size, density and porosity of the sediment. The sound speed of seawater at in situ measurement stations was calculated using a perennially averaged seawater sound speed map by an interpolation method. Moreover, empirical relations between the index of impedance and the sound speed and the physical properties were established. The results confirmed that the existing empirical equations between the in situ sound speed ratio and the density and porosity have general suitability for application. This study also considered that a multiple-parameter equation coupling the sound speed ratio to both the porosity and the mean grain size may be more useful for predicting the sound speed than an equation coupling the sound speed ratio to the mean grain size. 相似文献
18.
Short acoustical signals like those caused by explosions will in a waveguide split into mode arrivals. If the distance is long enough, they can at the receiver be resolved in time with appropriate narrowband filters. They can simultaneously be resolved in vertical angle (incidence-) with an endfire array and a beamformer. Combined in a beam-time diagram the arrivals will line up along a straight line. The slope of this line is invariant with frequency, mode indexes, source and receiver depths. It can conveniently be linked to the so-called waveguide invariant /spl beta/. An alternative approach to /spl beta/ is to compute it from the bathymetric profile. This is valid for range variable waveguides under adiabatic conditions, constant water sound speed over a harder bottom, and small grazing angles. Together these two approaches to /spl beta/ can be combined in a formula, where direct range determination is the end product. The applicability of the method is demonstrated on data from an experiment at sea. An 820-m array with 10 hydrophones was deployed at the bottom in 320-m water depth. For two endfire runs in opposite directions, small explosive charges out to 115 km were used as sound sources. Typical range estimation errors were 5-10%. 相似文献
19.
声波在海底界面的反射和透射是海底散射、海底混响、海底目标探测的重要问题。利用Biot多孔介质声传播理论对声波在水-多孔海底界面上的反射和透射进行了分析,具体给出反射声波的反射系数,3种透射声波的透射系数以及声能透射系数随入射波入射角和频率(10~40 kHz)的变化关系,分析了各种透射波对透射声能的贡献。多孔海底介质参数分别采用Stoll和Chotiros给出的2组参数进行理论计算。 相似文献
20.
为准确建立海底地声模型,本文探讨地声模型的基本组成和基本结构。通过样品实验室测量,分析南海海底表层沉积物的密度、孔隙度与声速随着埋深变化的关系,得出海底实际存在的低声速表面–声速缓慢变化类型、低声速表面–声速增大类型、高声速表面–声速缓慢变化类型和高声速表面–声速增大类型4种典型地声结构;对比钻探测量,分析黄海海底沉积物的密度、孔隙度与声速随埋深变化关系,得出海底地声模型分层特征与地声结构组合特征。研究表明,地声模型可以归结为4种基本地声结构的组合,通过与底层海水声速、同层内声速剖面以及与上层海底沉积物下表面声速的比较,可以建立各种海底地声模型;基于实验室测量法建立的地声模型可以作为参考地声模型,但需要考虑实际海底温度和压力梯度以及海底沉积物的频散特性等,借助于声速比校正法和频散性理论模型进行计算及修正。 相似文献