共查询到20条相似文献，搜索用时 250 毫秒
1.
Despite rapid progress in improving mass-storage density and digital communication system performance, compression of hydroacoustic image data is still significant in many engineering and research areas since it can overcome data storage and transmission bandwidth limitations. In this paper, we present a novel and effective approach for lossless compression of hydroacoustic image data which consists of two stages. The first stage reduces the information redundancy. We propose several new techniques to remove redundancy between data samples, data blocks, and data frames. The second stage uses a newly developed cascade coding scheme. This simple scheme can achieve an efficiency of 97%. A decomposition algorithm is presented for finding the optimal cascade coding parameters. The algorithm decomposes a multivariable optimization problem into a series of one-variable optimizations. Our two-stage algorithm offers a compression ratio of 2-3 and provides an exact recovery of the original data. Because of its simplicity, the algorithm can be incorporated into a variety of echo sounder systems. The compression algorithms can also be implemented using low-level assembly language to meet the requirements of real-time applications 相似文献
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High-frequency bubble layer scattering investigations require the measurement of the intensity of backscattered sound and the corresponding depth of the scatterers below the moving surface. Especially at high sea state conditions and high acoustic frequencies, bubbles acoustically mask the surface, i.e., the surface return cannot be detected. However, this environmental condition is the most interesting one in bubble scattering investigations and a reliable method is required to determine the range of the scatterers to the surface displacement. A method for the determination of the vertical profiling of acoustic scattering in the presence of bubbles at high sea state conditions is presented. It is based on the transmission of a low-frequency signal alternately to the high-frequency signal at which the scattering investigations are performed. The only information that is extracted from the low-frequency echo is the onset of the surface return. It is used to compute the true depth of scatterers at the high frequency. Experiments were conducted to determine the optimum low frequency at which the detection of the surface onset in the presence of a high bubble concentration is ensured. A screening ratio is defined to give a measure of the acoustic masking of the sea surface. It is depicted for an extreme wind condition (20 m/s) for the frequency range of 5-25 kHz and as a function of wind speed for 50 kHz measurements. Selected results of subsurface bubble scattering at 50 kHz from experiments under open sea conditions are presented for the wind speed regime from 9 to 22 m/s. Additionally, the two-frequency scatterometer is used to measure sea state characteristics simultaneously to the scattering investigations by remote sensing techniques 相似文献
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A. I. Gladkov 《Physical Oceanography》1995,6(4):319-323
A sequence of operations for the spectral and correlation estimation of digitized random signals is suggested using a fast Fourier transform. A set of algorithms and their possible modifications, which can be used in developing the spectral estimation programmes aimed at operative derivation of processing data is represented in compressed information form.Translated by Mikhail M. Trufanov. 相似文献
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The use of adaptive cluster sampling for hydroacoustic surveys 总被引：5，自引：0，他引：5
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Large-scale CTD survey data are used to calculate the acoustic velocity in the North Tropical Atlantic. It has been stated that a characteristic feature of the vertical hydroacoustic structure in this region is associated with the presence of numerous local sound channels in the subsurface and intermediate layers. Characteristics of these channels are given and possible causes of their origin are discussed. It is shown how local acoustic waveguides affect the sound beam trajectory.Translated by V. Puchkin. 相似文献
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A classification based on the number and types of large-scale acoustic waveguides is proposed for the mean seasonal profiles of sound speed propagation. A scheme for North Atlantic zoning, using typical curves of the sound speed vertical distribution, is given. The channel axis's position is shown not to depend on the water mass haline properties, being controlled by the temperature field vertical stratification.Translated by Vladimir A. Puchkin. 相似文献
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S. V. Semkin V. P. Smagin V. N. Savchenko 《Izvestiya Atmospheric and Oceanic Physics》2008,44(2):255-259
The feasibility of generating additional acoustic harmonics in the geomagnetic field during the propagation of an acoustic wave in a conducting medium through a region with a variable electromagnetic field is considered. Two possible mechanisms of such generation are analyzed: a parametric mechanism and a mechanism associated with ponderomotive forces (dynamic). Expressions are derived for three acoustic harmonics generated by a magnetic dipole with a variable magnetic moment. 相似文献
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《African Journal of Marine Science》2013,35(1):387-393
Unusual and distinct hydroacoustic targets were observed in November 1996, May 1998 and November 1998 during routine pelagic biomass surveys off the south coast of South Africa. During the November 1996 survey, seven such targets were observed near the bottom at depths of 115–125 m, directly south of the traditional inshore spawning grounds of chokka squid Loligo vulgaris reynaudii at Cape St Francis. The targets were close to prominent seabed ridges and extended 30–40 m off the bottom. In May 1998, three similar targets were observed at depths 55–80 m off Plettenberg Bay, another well-known squid spawning site. The shallowest target was identified, by means of a midwater trawl, as a mixture of mature male and female chokka. During the November 1998 survey, nine similar targets were again observed on the squid spawning grounds at Cape St Francis, also adjacent to seabed ridges. Drawing on fisheries hydroacoustic experience and knowledge of chokka squid spawning behaviour, the targets are believed to be aggregations of spawning squid. 相似文献
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The hydroacoustic method for the quantification of the gas flux from a submersed bubble plume 总被引：2，自引：0，他引：2
This article presents an inverse hydroacoustic method for the remote quantification of the total gas flux transported from
an underwater bubble plume. The method includes the surveying of the bubble plume by a vertically looking echo sounder and
the calculation of the flux using the spatial distribution of the ultrasound backscattering at a fixed depth. A simplified
parameterization containing only a few parameters is introduced to describe the empirical bubble size distribution. The linear
correlation between the backscattering cross section of the bubble stream and the vertical gas flux is found. The calculation
procedure takes into account the occurrence of a gas hydrate film at the bubble’s surface. The influence of different parameters
on the accuracy of the method is investigated. The resolution volume of the echo sounder corresponding to the fixed distance
is considered as a two-dimensional spatial window. The method was applied to quantify the total convective methane flux at
the Haakon-Mosby mud volcano (HMMV) depth 1280 m. The calculated values of the total flux near the bottom (100–400 t/year)
are in good agreement with the independently estimated flux for the single bubble jet observed from the ROV (70 t/year). These
calculations also show significant temporal variability of the flux at the HMMV. The total flux was found to vary by about
a factor of 2–3 within time scales of days. 相似文献
11.
Geoscience Australia (GA) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) conducted a marine survey including monitoring hydroacoustic flares in order to understand the natural leakage pathways in the offshore northern Perth Basin. 186 hydroacoustic contacts were encountered and classified and thirty two were interpreted as possible seeps or expulsion of gases from the subsurface. The contacts were typically distributed above areas of interpreted subsurface faulting. In the survey site Da (15 km2), nine probable seeps and sixteen other contacts were interpreted and are aligned with a fault segment (A2) interpreted on 2D seismic reflection data. The segment A2 is part of a major N–NNW trending fault system intersecting the sedimentary sequence from the near seabed to the Permian units, including the Kockatea Shale source rock located in the oil window. Evaluation of the stress state on the fault segment A2 suggests that it is not critically stressed and therefore not likely prone to reactivation and dilation and vertical leakage under the modelled stress field. We propose that fault segment A2 acts as a baffle delimiting a migration pathway in the wall rock and permitting hydrocarbons generated from the source rock to overcome capillary entry pressures of the overlying marginal seals. The interpreted seeps could therefore be associated with intraformational vertical migration in the wall rock focused by the faults. 相似文献
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Seismicity in ocean ridge-transform systems reveals fundamental processes of mid-ocean ridges, while comparisons of seismicity in different oceans remain rare due to a lack of detection of small events. From 1996 to2003, the Pacific Marine Environmental Laboratory of the National Oceanic and Atmospheric Administration(NOAA/PMEL) deployed several hydrophones in the eastern Pacific Ocean and the northern Atlantic Ocean.These hydrophones recorded earthquakes with small magnitudes, providing us with... 相似文献
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By using the hydroacoustic field generated by a point source in a nonuniform marine medium with a cylindrical body floating
on the surface and determined as a solution of the corresponding problem by the method of partial domains, we study the energy
characteristics of the near and far fields. The asymptotics capable of improving the accuracy of calculations is proposed
for the analysis of the posed problem for an infinite system of linear algebraic equations. We also present some results of
numerical calculations for some special cases and their comparative analysis in the case of variation of the parameters of
a waveguide within the ranges typical of the coastal zone of the sea.
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Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 52–59, May–June, 2006. 相似文献
16.
Data conflicts in fishery models: incorporating hydroacoustic data into the Prince William Sound Pacific herring assessment model 总被引：2，自引：0，他引：2
Hulson Peter-John F.; Miller Sara E.; Quinn Terrance J. II; Marty Gary D.; Moffitt Steven D.; Funk Frederick 《ICES Journal of Marine Science》2008,65(1):25-43
17.
The variability of the sound speed vertical distribution in high-salinity and freshened tropical waters has been computed using the intense convection model. It is shown that the most complicated transformation of theC(z) profile is induced by haline convection in freshened oceanic waters. Computation results are collated with observed data.Translated by Mikhail M. Trufanov. 相似文献
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探讨了壳寡糖及全乙酰壳寡糖的制备方法,通过正交实验考察了原料、温度、时间对降解产物的影响.制备了八种寡糖（八乙酰壳二糖、十一乙酰壳三糖、十四乙酰壳四糖和十七乙酰壳五糖,以及N,N′-二乙酰壳二糖、N,N′,N″-三乙酰壳三糖、N,N′,N″,N′′′四乙酰壳四糖和N,N′,N″,N′′′,N′′′′-五乙酰壳五糖）,并通过IR、NMR及MS等确定了其化学结构. 相似文献