共查询到20条相似文献,搜索用时 15 毫秒
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《Oceanic Engineering, IEEE Journal of》2009,34(4):407-422
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《Oceanic Engineering, IEEE Journal of》2009,34(4):451-458
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Evaluation of Laser Scanning and Stereo Photography Roughness Measurement Systems Using a Realistic Model Seabed Surface 总被引:1,自引:0,他引:1
《Oceanic Engineering, IEEE Journal of》2009,34(4):466-475
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《Oceanic Engineering, IEEE Journal of》2009,34(4):485-494
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《Oceanic Engineering, IEEE Journal of》2008,33(2):224-231
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《Oceanic Engineering, IEEE Journal of》2009,34(4):476-484
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《Oceanic Engineering, IEEE Journal of》2008,33(2):69-88
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Kelvin wake is one of the common wakes generated by moving ships and contains rich information about ships. In this paper, free wave elevations of Kelvin wake are calculated based on the Michell thin ship theory combined with a point source perturbation model. The probability density function of sea surface slopes is introduced to calculate the specular reflection of sunlight and skylight and the refraction of scattered light underwater. Satellite-detected Kelvin wakes are then simulated by adding surface specular reflectance and water-leaving reflectance. Simulation results agree well with satellite measurements. The specular reflection of sunlight is the decisive factor affecting the features of Kelvin wakes according to the simulation results. The main factors that influence the specular reflection of sunlight, such as the incident direction and observation direction, ship parameters, and background environment, are discussed. This study is helpful for wake detection and provides a preliminary theoretical method for the retrieval of ship information. 相似文献
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A formulation is presented for evaluating the performance of acoustic data systems to determine the location and orientation of underwater research apparatus. The variables to describe the position of the underwater research apparatus are referenced to a surface ship, and represent the straight-line distance from the stern of the ship to a point on the apparatus (R ), the angular distance down from the sea surface (Phi ), and the angular distance from the direction of motion of the ship (Theta ). The three orientation variables on the apparatus are the angle between thez andz' axes (i ), the angle between thex andx' axes in thex'-y' plane (Omega ), and the angle which locates thex' axis in thex'-y' plane (omega ). A simple model for the sound velocity variation with depth is included in the range data analysis, while the Doppler data are shown not to need that further complication in the analysis. An error model is constructed and applied to three geometries which represent common underwater research devices. Accuracy goals for possible applications of these devices are discussed, and performance requirements for an acoustic system which would meet the goals are derived. 相似文献
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Distinct side-scan sonar, RADARSAT SAR, and acoustic profiler signatures of gas and oil seeps on the Gulf of Mexico slope 总被引:4,自引:0,他引:4
S. M. De Beukelaer I. R. MacDonald N. L. Guinnasso Jr. J. A. Murray 《Geo-Marine Letters》2003,23(3-4):177-186
We examined bubble streams from four natural seep sites on the upper continental slope of the Gulf of Mexico. Synthetic aperture radar images verified surface oil slicks over sites with oily bubbles but not over those with non-oily bubbles. Non-oily bubbles produced high backscatter on side-scan sonar records, but were difficult to detect with acoustic profilers. Oily bubbles produced clear signatures extending from the seafloor to the near-surface on acoustic profiles and produced acoustic shadows on side-scan sonar records. We hypothesize that the bubbles oily coating causes the different signatures, since all bubbles were resonant at the tested frequencies. 相似文献
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A coastal acoustic tomography experiment in the Tokyo Bay 总被引:1,自引:0,他引:1
KANEKO Arat YAMAGUCHI Keisuke YAMAMOTO Tokuo GOHDA Noriaki ZHENG Hong SYAMSUDIN Fadli LIN Ju NGUYEN Hong-Quang MATSUYAMA Masaji HACHIYA Hiroyuki HASHIMOTO Noriaki 《海洋学报(英文版)》2005,24(1):86-94
Eight sets of coastal acoustic tomography (CAT) systems were deployed during November 29 to December 10, 2002 at the coasts on both sides of Tokyo Bay to measure tidal current structures at 15-rain interval.Sound transmission across the Tokyo Bay (between Yokohama and Chiba)was successfillly traced,even under severe interference from ship generated wakes and bubbles.Tidal current fields changing from northward to southward flow are well reconstructed by the inverse analysis of travel-time difference data for a period with the best sound transmission condition. It is suggested that the CAT is the most powerful tool to continuously map tidal current fields in the coastal seas with heavy shipping traffic and fisheries activity. 相似文献
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The paper summarizes the results of the long-term complex satellite monitoring of the Black and Baltic seas. Data from synthetic aperture radars (SARs) constitute the experimental basis for the investigation of satellite. In addition to radar data, the data of the visible and infrared bands from MODIS Terra/Aqua, MERIS Envisat, Landsat series sensors are used. The features of the manifestation of hydrodynamic processes, submesoscale eddies in particular, in satellite radar and optical images in a period of intense phytoplankton bloom are discussed. A relationship is established between the intensity and duration of the phytoplankton bloom in the regions of observation and the frequency of the appearance of long-lasting wakes behind moving ships in SAR images. These wakes appear as long narrow bright bands of enhanced backscattered signal extending for tens and sometimes hundreds of kilometers. It is proposed to consider the wakes of this type as indicators of the areas and duration of intense phytoplankton bloom. Satellite observations over the Black and Baltic Seas conducted for more than ten years have shown that long-lasting ship wakes are influenced by powerful jet streams, such as those associated with the passage of eddies that leads to shifts and deformations. By comparing the true route of a ship with its wake in the satellite image, it is possible to obtain detailed information about the parameters of currents. 相似文献
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Systems of identical precisely spaced bubbles or similar monopole scatterers in water-e.g., inflated balloons or thin-walled shells-insonified at frequenciesomega_{SR} dose to their fundamental radial resonanceomega_{0} (bubble) frequency may themselves display resonance modes or superresonances (SR's) [1]. Ordinary single-bubble resonances magnify the local free-field pressure amplitudep_{1} by a factor(ka)^{-1} ,a being the radius andk the wavenumber in water: for air bubbles or balloons in water, this factor is of the order of 70. Under SR conditions each member of the system amplifies the local free-field amplitude by a further factor of order(ka)^{-1} . Depending upon geometry and other constraints, the pressure fieldP_{SR} on the surface and in the interior of each scatterer will then be in the range of10^{3}p_{1} to5 times 10^{3} p_{1} . This paper investigates the sensitivity of this phenomenon to small departures from the ideal model. In particular, it examines the effect of small differences in scatter positioning and volumes in the context of an SR system consisting of two bubbles/balloons close to the boundary of a thin elastic plate overlying a fluid half-space. It is found that, to observe the SR phenomenon, radii and positions should be controlled to within approximately 1/2 percent.P_{SR} is also sensitive to the angle of incidence of the plane wave train. For the simple system examined here, this sensitivity is considerable for either flexural wave trains or volume acoustic waves incident upon the bubble/ balloon pair (doublet). Practical uses of the phenomenon may range from the design of passive high-Q acoustical filter/amplifiers and acoustical lenses to improved source efficiencies. 相似文献
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Kelvin尾迹SAR多视向的成像仿真 总被引:1,自引:0,他引:1
利用船只Kelvin航迹模型、海面波模型和二尺度微波散射模型,提出了船尾迹多视向的成像仿真技术,并首次在二维空间中从不同视向仿真船尾迹的SAR图像。结果表明,当雷达视向与船只航向平行时,横波成像明显;当雷达视向与船只航向垂直时,扩散波成像明显;当雷达视向与船只航向有个夹角时,会出现一臂亮一臂暗的现象,这一现象取决于两臂尖波的传播方向与雷达视向的夹角,传播方向与雷达视向越接近平行的波越容易被雷达观测到,从而形成亮臂。仿真结果还得出另外一个结论:船只航向与雷达视向越接近垂直,两臂张角越小。仿真结果和实际的多幅ERS-SAR图像所观测到的结果是一致的。该模型可以有效地模拟Kelvin尾迹SAR多视向成像。 相似文献
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浅层气逸出到海水中的气泡声学探测方法 总被引:4,自引:0,他引:4
针对南黄海西部等地区在海洋调查仪器上发现的海水中浅层气逸出气泡产生的声学羽流等气泡记录,首先根据水体中气泡共振发生非线性振动形成的强烈散射现象,计算了我国浅层气分布海区的常见浅层气逸出气泡共振频率范围、不同调查仪器在水深变化时的探测气泡大小,据此分析了不同调查仪器探测浅层气逸出气泡的范围。其次,根据气泡在水中的变化、运动规律,提出了浅层气逸出气泡应当具备的声学特点,排除了南黄海西部地区形成水体中特征反射的其他可能因素,并探讨了云状扰动的可能形成原因。 相似文献
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We studied the time dynamics of a turbulent region excited by a moving surface vessel in a field experiment. The time dependences
of the geometrical sizes of the turbulent region are obtained, and it is shown that the time dependence of the width of the
turbulent wake at the initial stage is close to the power-law function with an exponent of 0.4 for different experiments (the
depth of the wake remaining practically constant). In the semiempirical turbulence theory, we suggested a qualitative model
describing the process of the initial expansion of a ship wake as a diffusion of a one-dimensional layer of turbulized liquid
due to a pulsed source. 相似文献
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The design and use of a marine heat probe with capability for measuring thermal conductivity insitu with high accuracy, and providing digital acoustic transmission of data to the ship, is described. The instrument employs the violin bow strength member and parallel sensor string configuration suggested by C. R. B. Lister. Several hundred measurements have been made in the deep ocean on multipenetration or pogostick profiles using a 3 m probe and in deep inlets of western Canada using a 7 m probe. The insitu thermal conductivity technique using a calibrated heat pulse has been studied in detail through laboratory calibration of the probe in materials of known conductivity, through numerical models, and through comparison of insitu measurements with needle probe measurements on sediment cores taken from the same sites. The insitu technique permits a conductivity accuracy of better than ±5% with a recording time of 7 minutes following 7 minutes in the bottom to establish the geothermal gradient. The pulse heating is also more energy efficient than the conventional continuous heating technique.Contribution from the Earth Physics Branch No. 807. 相似文献