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1.
Acoustic volume backscattering strength data were collected and Conductivity Temperature Depth (CTD) measur e m e n t s were
conducted in the southern Yellow Sea in summer 2005 and 2006. The high temporal and vertical resolution acoustic data measured
with a 307 kHz Acoustic Doppler Current Profiler (ADCP) and a 250 kHz acoustic Doppler profile (ADP) had dominant diel variation,
which resulted from vertical migration of sound scatterers. Some scatterers congregating in the bottom layer in the daytime
migrated upward at dusk, and migrated downward into the bottom layer at dawn. The migration speeds were estimated. More than
33 days data show that the diel migration varies with time. The feature of migration measured with ADCP and ADP is consistent
to some extent with what is described in the study on vertical migration of zooplankton in the southern Yellow Sea with conventional
net samples. 相似文献
2.
Three decades of continuous ocean exploration have led us to identify subsurface fluid related processes as a key phenomenon in marine earth science research. The number of seep areas located on the seafloor has been constantly increasing with the use of multi-scale imagery techniques. Due to recent advances in transducer technology and computer processing, multibeam echosounders are now commonly used to detect submarine gas seeps escaping from the seafloor into the water column. A growing number of en-route surveys shows that sites of gas emissions escaping from the seafloor are much more numerous than previously thought. Estimating the temporal variability of the gas flow rate and volumes escaping from the seafloor has thus become a challenge of relevant interest which could be addressed by sea-floor continuous acoustic monitoring. Here, we investigate the feasibility of estimating the volumetric flow rates of gas emissions from horizontal backscattered acoustic signals. Different models based on the acoustic backscattering theory of bubbles are presented. The forward volume backscattering strength and the inversion volumetric flow rate solutions were validated with acoustic measurements from artificial gas flow rates generated in controlled sea-water tank experiments. A sensitivity analysis was carried out to investigate the behavior of the 120-kHz forward solution with respect to model input parameters (horizontal distance between transducer and bubble stream, bubble size distribution and ascent rate). The most sensitive parameter was found to be the distance of the bubble stream which can affect the volume backscattering strength by 20 dB within the horizontal range of 0–200 m. Results were used to derive the detection probability of a bubble stream for a given volume backscattering strength threshold according to different bubble flow rates and horizontal distance. 相似文献
3.
P. Dewangan T. RamprasadM.V. Ramana A. MazumdarM. Desa F.K. Badesab 《Marine and Petroleum Geology》2010
Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, Krishna–Godavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor. 相似文献
4.
Wiebe P.H. Stanton T.K. Benfield M.C. Mountain D.G. Greene C.H. 《Oceanic Engineering, IEEE Journal of》1997,22(3):445-464
High-frequency (120 and 420 kHz) sound was used to survey sound scatterers in the water over Georges Bank. In addition to the biological sound scatterers (the plankton and micronekton), scattering associated with internal waves and suspended sediment was observed. Volume backscattering was more homogeneous in the vertical dimension (with occasional patches) in the shallow central portion of the Bank where there is significant mixing. In the deeper outer portion of the Bank where the water is stratified, volume backscattering was layered and internal waves modulated the vertical position of the layers in the pycnocline. The internal waves typically had amplitudes of 5-20 m, but sometimes much higher. Species composition and size data from samples of the animals and suspended sediment used in conjunction with acoustic scattering models revealed that throughout the region the animals generally dominate the scattering, but there are times and places where sand particles (suspended as high as up to the sea surface) can dominate. The source of the scattering in the internal waves is probably due to a combination of both animals and sound-speed microstructure. Determination of their relative contributions requires further study 相似文献
5.
An ahead-looking probe of some kind, optical or acoustic, is critical when one is attempting seafloor exploration from a mobile platform. A single-frequency, split aperture sonar system can be used for this purpose, but a wideband monopulse sonar offers many advantages. It computes a running estimate of the vertical directional cosine of the source of the echo, and can thus reveal the positions of multiple wave scatterers as long as their echoes can still be time resolved. Theoretical studies of its performance have been made previously, but were directly applicable only to extremely simple seafloor geometries. A new time-domain digital simulation that largely circumvents this limitation has been developed. The simulation also provides a means for testing the theory and optimizing system parameters. The reverberation model does not account for some features of acoustic backscattering such as diffraction, but it is believed to be adequate for the investigation of most signal processing aspects of the sonar system. The theory of the simulation is developed and several examples are presented and discussed. In addition, some preliminary results are presented from a sea test that used the air-sea interface as a surrogate seafloor 相似文献
6.
孙瀛 《海洋学报(英文版)》1987,6(2):266-272
The method of acoustic backscattering measurement from different parts of fish using the focus array of transducer developed recently is described in this paper. The results of the measurements of several kinds of flsh are given in this paper, indicating that the backscattering from fish is closely relative to the anatomy of fish. Its application in forming backscattering model of fish and that in using this model to obtain the information of fish kinds by the echoes from fish sonar are discussed. 相似文献
7.
A comparison of the contribution of zooplankton and nekton taxa to the near-surface acoustic structure of three Turkish seas 总被引：1，自引：0，他引：1
Erhan Mutlu 《Marine Ecology》2005,26(1):17-32
The bioacoustics of upper waters of the Black Sea, the Sea of Marmara, and the Mediterranean Sea were studied in October 1999 with an echosounder with 120 and 200 kHz dual‐beam transducers. Net tows were taken to ground‐truth the acoustic volume backscattering. A forward solution was applied to determine significant scatterers of the three seas with regard to detection limits of the frequencies and background noise measured in each sea. The noise was 4 dB higher in the Sea of Marmara than in the other two seas. 200 kHz data showed significant correlation between measured and calculated volume backscattering strength, and density (biomass and abundance) of the taxa. Large‐sized copepods and chaetognaths in the Black Sea, Aurelia, Beroe, chaetognaths and large‐sized and abundant appendicularians in the Sea of Marmara, and fish larvae in the Mediterranean Sea contributed most to the volume backscattering. 相似文献
8.
9.
High-resolution acoustic measurements of low-frequency near-surface backscattering at low grazing angles have been made in the open ocean using vertical arrays of coherent sources. Over the range of wind speeds (4-18 m/s) encountered, the normalized data amplitudes exhibited variable non-Rayleigh behavior, from near Rayleigh in the highest sea states to near lognormal in low-to-moderate sea states. Seven probability density function (pdf) models were fit to the data, with the three-component Rayleigh mixture providing the most consistent fits and the least errors. One pdf model, the Poisson-Rayleigh, provided not only good fits to many data sets, but also physical insights into the scattering process. This model's estimates of the expected number of discrete scatterers ranged from 200/km/sup 2/ at low wind speeds to 2000/km/sup 2/ at high wind speeds, consistent with the expected densities of fish and subsurface bubble clouds, respectively. These results are encouraging with regard to developing physical models capable of using local results (such as these) to accurately predict long-range reverberation and clutter statistics. 相似文献
10.
S. Garcia-Gil 《Geo-Marine Letters》2003,23(3-4):215-229
Interpretation of acoustic seismic records have allowed mapping of shallow gas accumulations and gas escape features in the Rías Baixas. X-ray photographs and voids of cores are semi-direct evidence of gassy sediments. Mapping of fluid-escape areas shows that these are related to the gas accumulations or at the intersections of faults. Analyses (GC-MS) of bubble samples collected in Simón Bay (Ría de Vigo) and across the whole ría confirm the presence of methane. The spatial distribution of gas escapes/accumulations and their vertical variations are interpreted as evidence of sedimentary facies control. The appearance of authigenic minerals (gypsum, pyrite and aragonite) and microbiological activity related to the seal facies are taken as evidence of the biogeochemical coupling processes. It is evident that these shallow-water coastal environments make significant contributions to the methane budget of the hydrosphere and atmosphere. It is also suggested that microbiological activity is favoured by gas escapes. 相似文献
11.
Experimental measurements of the bottom backscattering strength from carbonate sediments were made with a 200-kHz multibeam
sonar mounted on a remotely operated vehicle. Results were obtained from eight different sites, which may be grouped into
three categories, labeled soft, medium and hard, according to measured sediment sound speed. Sediment samples were gathered
at or near each site to help interpret the acoustic results. The acoustic results are compared with extant published data
and with the BOGGART bottom backscatter model. Backscattering strength values measured in the soft and medium sites fell within
the main cluster of previously published values from sediments of similar grain sizes. The values from the hard region fell
close to the upper limit. Dependence of the apparent backscattering strength on sonar height above bottom, particularly for
the lower values of height above bottom, was observed, which suggests that the scattering process is a multiple-scattering
one. 相似文献
12.
Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these studies have been barely carried in the Bohai Sea. The sea-ice microwave scattering mechanism was first developed for the thin sea ice with slight roughness in the Bohai Sea in the winter of 2012, and included the backscattering coefficients which were measured on the different conditions of three bands(L, C and X), two polarizations(HH and VV), and incident angles of 20° to 60°, using a ground-based scatterometer and the synchronous physical parameters of the sea-ice temperature, density, thickness, salinity, and so on. The theoretical model of the sea-ice electromagnetic scattering is obtained based on these physical parameters. The research regarding the sea-ice microwave scattering mechanism is carried out through two means, which includes the comparison between the field microwave scattering data and the simulation results of the theoretical model, as well as the feature analysis of the four components of the sea-ice electromagnetic scattering. It is revealed that the sea-ice microwave scattering data and the theoretical simulation results vary in the same trend with the incident angles. Also, there is a visible variant in the sensitivity of every component to the different bands.For example, the C and X bands are sensitive to the top surface, the X band is sensitive to the scatterers, and the L and C bands are sensitive to the bottom surface, and so on. It is suggested that the features of the sea-ice surfaces and scatterers can be retrieved by the further research in the future. This experiment can provide an experimental and theoretical foundation for research regarding the sea-ice microwave scattering characteristics in the Bohai Sea. 相似文献
13.
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
14.
概述了应用子波分析对悬浮物测量中的声散射信号进行特征提取的方法 ,并对声散射信号识别的研究进行了探讨。对实测数据的实验取得了较好的结果 相似文献
15.
水体悬沙浓度是水利、环境、河口海岸与海洋相关研究领域最为基础的数据需求之一。随着传感器技术的发展, 悬沙浓度连续测量技术在悬沙浓度测量领域表现出高时空分辨率、长期数据采集的成本和风险均较低的突出优点。本文综述了光学、声学、音叉谐振、压差和放射性射线衰减等原理用于悬沙浓度连续测量技术的相关研究进展, 探讨了各技术方法的优、缺点, 并提出了今后的研发重点和发展方向主要在以下几个方面: 1) 光后向散射原理是低成本、小型化和高时频测量悬沙浓度的最优技术路线, 需着力于开展量程扩增和粒径敏感度削弱研究; 2) 低不确定度悬沙浓度垂向剖面观测的实现依赖于超声后向散射原理技术路线的发展; 3) 音叉谐振原理技术路线尤为契合高含沙水流和浮泥工况下的超高量程应用场景; 4) 多技术路线传感器融合以及使用人工智能算法模型替代正向反演模型。 相似文献
16.
Hydroacoustic methods are particularly suitable for investigations of the occurrence, cyclicity and amount of bubbles released at cold seeps without disturbing them. Experiments with a horizontally looking single beam transducer (40 and 300 kHz) directed towards artificially produced bubbles show that the backscattering strength of the bubbles increases with the gas flux rate independently of the bubble radii distribution. It is demonstrated that an acoustic system can be calibrated in such a way that gas flux rates of bubble-size spectra, as observed at natural seeps, can be directly related to the echo level of a known, acoustically insonified volume. No system-specific parameters have to be known except the beam width. 相似文献
17.
Sea-surface acoustic backscattering measurements at moderate to high frequencies were performed in the shallow water of the south Yellow Sea, using omnidirectional spherical sources and omnidirectional hydrophones. Sea-surface backscattering data for frequencies in the 6–25 k Hz range and wind speeds of(3.0±0.5)and(4.5±1.0) m/s were obtained from two adjacent experimental sites, respectively. Computation of sea-surface backscattering strength using bistatic transducer is described. Finally, we calculated sea-surface backscattering strengths at grazing angles in the range of 16°–85°. We find that the measured backscattering strengths agree reasonably well with those predicted by using second order small-roughness perturbation approximation method with "PM" roughness spectrum for all frequencies at grazing angles ranged from 40° to 80°. The backscattering strengths varied slightly at grazing angles of 16°–40°, and were much stronger than roughness scattering. It is speculated that scattering from bubbles dominates the backscattering strengths at high wind speeds and small grazing angles. At the same frequencies and moderate to high grazing angles, the results show that the backscattering strengths at a wind speed of(4.5±1.0) m/s were approximately 5 d B higher than those at a wind speed of(3.0±0.5) m/s. However, the discrepancies of backscattering strength at low grazing angles were more than 10 d B. Furthermore the backscattering strengths exhibited no significant frequency dependence at 3 m/s wind speed. At a wind speed of 4.5 m/s, the scattering strengths increased at low grazing angles but decreased at high grazing angles with increasing grazing angle. 相似文献
18.
声遥测水中悬浮粒子（如泥沙）的反向散射强度,可反演获得粒子浓度。可是,遥测系统对采样体积采集的声反向散射,除了粒子的散射信号外,还包含附加的干扰和噪声。本文探讨采集悬浮粒子声反向散射信号时,如何降低干扰源和噪声源对其影响的若干对策。 相似文献
19.
ADCP对悬浮沉积物浓度的测量及其误差分析研究 总被引：6，自引：0，他引：6
为实时、连续地测量海水中悬浮沉积物,利用声学多普勒海流剖面仪(ADCP),可以在测流的同时,测量海洋悬浮沉积物浓度。描述了利用后散射强度,估计悬浮沉积物浓度的原理。在现场测试中,利用采水器采集水样,通过水样分析并结合声信号的衰减特征对AI)CP的测量结果进行修正。作者还结合现场测试结果,对这一测量方法的精度进行了分析。现场实验表明,经公式校正后,ADCP测得的后散射强度与实测水样所获得的悬浮沉积物浓度之间有很好的相关性,相关系数达0．88,由此证明,此测量方法具有很好的实用价值和应用前景。 相似文献
20.