共查询到18条相似文献，搜索用时 203 毫秒
1.
The brightness reversal of submarine sand waves appearing in the small satellite constellation for environment and disaster monitoring and forecasting("HJ-1A/B") CCD sun glitter images can affect the observation and depth inversion of sand wave topography. The simulations of the normalized sun glitter radiance on the submarine sand waves confirm that the reversal would happen at a specific sensor viewing angle, defined as the critical angle. The difference between the calculated critical angle position and the reversal position in the image is about 1, which is excellent in agreement. Both the simulation and actual image show that sand wave crests would be indistinct at the reversal position, which may cause problems when using these sun glitter images to analyze spatial characteristics and migration of sand waves. When using the sun glitter image to obtain the depth inversion, one should take the advantage of image properties of sand waves and choose the location in between the reversal position and the brightest position. It is also necessary to pay attention to the brightness reversal when using "HJ-1A/B" CCD images to analyze other oceanic features, such as internal waves, oil slicks, eddies, and ship wakes. 相似文献
2.
Lin Mingchung Hsiao Sungshan Hsu Yungcheng
Professor Dept. of Naval Architecture Ocean Engineering National Taiwan University Taiwan. Doctor Course Student Dept. of Naval Architecture Ocean Engineering National Taiwan University Taiwan 《中国海洋工程》1994,(3)
-Wave refraction-diffraction due to a large ocean structure and topography in the presence of a 'current are studied numerically. The mathematical model is the mild-slope equation developed by Kirby (1984). This equation is solved using a finite and boundary element method. The physical domain is devid-ed into two regions: a slowly varying topography region and a constant water depth region. For waves propagating in the constant water depth region, without current interfering, the mild- slope equation is then reduced to the Helmholtz equation which is solved by boundary element method. In varying topography region, this equation will be solved by finite element method. Conservation of mass and energy flux of the fluid between these two regions is required for composition of these two numerical methods. The numerical scheme proposed here is capable of dealing with water wave problems of different water depths with the main characters of these two methods. 相似文献
3.
A simulation of radiation imagery for ocean color satellite 总被引：2，自引：0，他引：2
The ocean color satellite is mainly applied to measure the water constituents such as chlorophyll, suspended material and yellow substance. The leaving water radiance is very small part of the total radiance arrival at the sensor about 3%-15%,and depends on the properties of the orbit and sensor. Before the satellite is launched on the orbit, it needs to simulate the radiation imagery in order to evaluate the quality and availability of the satellite data.
If the parameters of satellite orbit, the properties of sensor as well as the characteristics of the atmosphere and water have been known, the radiation scattered by air molecule and aerosol, reflected solar radiation, water leaving and total radiation arriving at the sensor can be simulated by the models of radiation transfer in the atmosphere, air/water and subsurface water. In this paper, the mechanism, models and procedures of the radiation simulation are first discussed and employed to simulate a series of imageries for the Chinese satellites FY-lA, FY-1B, and ROCSAT-1 (Taiwan, China), and American satellite Ses STAR. Their results show that the solar irradiance arrived at water surface and the sun glitter mainly affect the quality and availability of satellite data, which depend on the orbit properties. Finally, some suggestions are proposed to improve the quality and availability of a:ean color satellite data. 相似文献
If the parameters of satellite orbit, the properties of sensor as well as the characteristics of the atmosphere and water have been known, the radiation scattered by air molecule and aerosol, reflected solar radiation, water leaving and total radiation arriving at the sensor can be simulated by the models of radiation transfer in the atmosphere, air/water and subsurface water. In this paper, the mechanism, models and procedures of the radiation simulation are first discussed and employed to simulate a series of imageries for the Chinese satellites FY-lA, FY-1B, and ROCSAT-1 (Taiwan, China), and American satellite Ses STAR. Their results show that the solar irradiance arrived at water surface and the sun glitter mainly affect the quality and availability of satellite data, which depend on the orbit properties. Finally, some suggestions are proposed to improve the quality and availability of a:ean color satellite data. 相似文献
4.
A new approach to detecting ocean eddies automatically from remote sensing imageries based on the ocean eddy's eigen-pattern in remote sensing imagery and "force field-based shape extracting method" is proposed. First, the analysis on extracting eddies' edges from remote sensing imagery using conventional edge detection arithmetic operators is performed and returns digitized vector edge data as a result. Second, attraction forces and fusion forces between edge curves were analyzed and calculated based on the vector eddy edges. Thirdly, the virtual significant spatial patterns of eddy were detected automatically using iterative repetition followed by optimized rule. Finally, the spatial form auto-detection of different types of ocean eddies was done using satellite images. The study verified that this is an effective way to identify and detect the ocean eddy with a complex form. 相似文献
5.
Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction, especially the depth of the bottom cavity. In this study, a ship model experiment of a bulk carrier is conducted in a towing tank using the method of air layer drag reduction(ALDR) with different bottom cavity depths. The shape of the air layer is observed, and the changes in resistance are measured. The model experiments produce results of approximately 20%for the total drag reduction at the ship design speed for a 25-mm cavity continuously supplied with air at Cq = 0.224 in calm water, and the air layer covers the whole cavity when the air flow rate is suitable. In a regular head wave, the air layer is easily broken and reduces the drag reduction rate in short waves, particularly when λ/Lw1 is close to one;however, it still has a good drag reduction effect in the long waves. 相似文献
6.
Numerical simulation of breaking wave generated sediment suspension and transport process based on CLSVOF algorithm 总被引：1，自引：0，他引：1
The sediment suspension and transport process under complex breaking wave situation is investigated using large eddy simulation （abbreviated as LES hereafter） method. The coupled level set （LS） and volume of fluid （VOF） method is used to accurately capture the evolution of air？water interface. The wall effect at the bottom is modeled based on the wave friction term while the complicate bottom boundary condition for sediment is tackled using Chou and Fringer’s sediment erosion and deposition flux method. A simulation is carried out to study the sediment suspension and transport process under periodic plunging breaking waves. The comparison between the results by CLSVOF method and those obtained by the LS method is given. It shows that the latter performs as well as the CLSVOF method in the pre-breaking weak-surface deformation situation. However, a serious mass conservation problem in the later stages of wave breaking makes it inappropriate for this study by use of the LS method and thus the CLSVOF method is suggested. The flow field and the distribution of suspended sediment concentration are then analyzed in detail. At the early stage of breaking, the sediment is mainly concentrated near the bottom area. During the wave breaking process, when the entrapped large-scale air bubble travels downward to approach the bottom, strong shear is induced and the sediment is highly entrained. 相似文献
7.
基于X波段微波雷达的近海水深数值模拟与反演 总被引：2，自引：2，他引：0
8.
Parabolic Approximation of the Weakly Nonlinear Mild Slope Equation with Bottom Friction 总被引：2，自引：0，他引：2
This paper presents a refined parabolic approximation model of the mild slope equation to simu-late the combination of water wave refraction and diffraction in the large coastal region.The bottom frictionand weakly nonlinear term are included in the model.The difference equation is established with the Crank-Nicolson scheme.The numerical test shows that some numerical prediction results will be inaccurate in com-plicated topography without considering weak nonlinearity;the bottom friction will make wave height damp-ing and it can not be neglected for calculation of wave field in large areas. 相似文献
9.
Scour of the Seabed Under A Pipeline in Oscillating Flow 总被引：3，自引：0，他引：3
The scour of the seabed under a pipeline is studied experimentally in this paper. Tests are carried out in a U-shaped oscillatory water tunnel with a box imbedded in the bottom of the test section. By use of the standard sand, clay and plastic grain as the seabed material, the influence of the bed material on the scour is studied. The relationship between the critical initial gap-to-diameter ratio above which no scour occurs and the parameters of the oscillating flow is obtained. The self-burial phenomenon, which occurs for the pipeline not fixed to two sidewalls of the test section, is not observed for the fixed pipeline. The effect of the pipe on sand wave formation is discussed. The maximum equilibrium scour depths for different initial gap-to-diameter ratios, different Kc numbers and different bed sands are also given in this paper. 相似文献
10.
Based on the refraction-diffraction theory of irregular waves in the waters of slowly-varying cur-rents and depths,and the generation dissipation theory of wind wave,a model for nonlinear irregular wavesin coastal area is developed.In light of the specific conditions of coastal wave character and engineering ap-plication,a practical mathematical model for the nonlinear irregular waves is presented.with directional spec-trum in coastal area.Coast effect,refraction,whitecapping.bottom friction.current,wind and nonlinearaction are considered in this model.The numerical methods and schemes for wave refraction ray,energy con-servation of propagation,energy balance of the generation and dissipation of wind waves have been studied.Finally,the model is used for the directional wave spectrum computation in the Daya Bay.Compared withthe measured data with 956 wave bouys in the Daya Bay,the model results are in good agreement with themeasured results. 相似文献
11.
Osamu Abe Atsushi Watanabe V. V. S. S. Sarma Yohei Matsui Hiroya Yamano Naohiro Yoshida Toshiro Saino 《Journal of Oceanography》2010,66(3):363-372
We estimated gas exchange rates in Kabira Reef at Ishigaki Island, southwest Japan, using a mass balance calculation with
dual “biological” tracers: dissolved inorganic carbon (DIC) and dissolved oxygen (DO). The nighttime results allowed us to
obtain reasonable gas transfer velocity k
w values, all of which exceeded those obtained in wind-dominant studies. The difference is likely due to the contribution of
turbulence generated by the interaction between the current and bottom topography. The k
w obtained during high tides is consistent with that reported by Raymond and Cole (2001), whereas k
w during low tides is significantly higher, which seems to be caused by enhanced friction with the bottom of the reef and/or
bubble-induced gas transfer by wave breaking at the reef crest. 相似文献
12.
Keigh I. Ohshima 《Journal of Oceanography》1987,43(1):61-67
The stability of the Soya Warm Current is examined, in an attempt to explain the mechanism of the formation of the wave-like pattern seen in satellite infrared imagery in summer. A linear stability theory is applied to barotropic shear flows over a realistic bottom topography. Effects of bottom friction are also taken into consideration. For this current in summer, when volume transport is greatest, the possibility of barotropic instability is suggested. The most unstable waves obtained in this study have wavelengths of 60–80 km, periods of about 1. 5 days, and phase velocities of 45–55 cm sec–1, which is in good agreement with observations. 相似文献
13.
Otaki Takayoshi Hamana Masahiro Tanoe Hideaki Miyazaki Nobuyuki Shibuno Takuro Komatsu Teruhisa 《Ocean Science Journal》2015,50(2):327-334
Most demersal fishes maintain strong relations with bottom substrates and bottom depths and/or topography during their lives. It is important to know these relations to for understand their lives. In Tokyo Bay, red stingray, Dasyatis akajei, classified as near-threatened species by IUCN, has increased since the 1980s. It is a top predator and engages in ecosystem engineer by mixing the sand bed surface through burring behavior, and greatly influences a coastal ecosystem. It is reported that this species invades in plage and tidal flats and has sometimes injured beachgoers and people gathering clams in Tokyo bay. Thus, it is necessary to know its behavior and habitat use to avoid accidents and to better conserve the biodiversity of ecosystems. However, previous studies have not examined its relationship with the bottom environment. This study aims to describe its behavior in relation to the bottom environment. We sounded three dimensional bottom topography of their habitat off Kaneda Cove in Tokyo Bay with interferometric sidescan sonar system and traced the movement of red stingrays by attaching a data logger system to survey their migration. The results revealed that red stingray repeated vertical movement between the surface and bottom, and used not only sand beds but also rocky beds.
相似文献14.
A bottom longline fishery operated in the EEZ of New Caledonia from 1988 to 1991. Fishing focused on five seamounts with summits at depths ranging from 500 to 750 m. The target species was alfonsino, Beryx splendens. As the soundings available from marine charts were not detailed enough, the fishing masters had to make their own charts in order to set the gear in the right location. A series of 11 scientific cruises devoted to a research program on alfonsino was launched in late 1991. During the first scientific cruises, several days were spent mapping the seabed to improve the existing knowledge of the topography of three seamounts by coupling the EDO echosounder depth measurements to the GPS positions. As this procedure is slow, it is applicable to limited areas or, if a wider grid is used, to large zones to locate major structures such as ridges and seamounts. The emergence of the multibeam echosounder has greatly improved seabed mapping performance. This tool seems to fit the requirement of exploratory deep-bottom fishing particularly well, as it covers large areas while providing details of the bottom. The EM 12 was used to obtain bathymetry and imagery of the SE portion of the EEZ of New Caledonia, covering an approximate area of 70,000 km2 in two weeks. For depths ranging from 500 to 4,500 m, the results were impressive. They confirmed the known major features and provided greater topographical detail, revealing fine unknown structures. They also provided information on the type of substratum, information which might influence the fishing strategy. Finally, they made it possible to obtain an accurate estimate of the exploitable area which in turn led to new stock estimates. 相似文献
15.
卫星海洋水色遥感的辐射模式研究 总被引：6，自引：3，他引：6
海洋水体向上的辐射由水中多种成分的浓度所决定，同时辐射的强度十分微弱并随着时间和空间在变化。因此，海洋水色遥感需要从水体和大气辐射传递机理出发，研究到达卫星遥感器的辐射模式，以达到模拟仿真卫星水色遥感图像和卫星图像质量预测的目的。本研究通过叶绿素、悬浮泥沙和黄色物质等海洋水色的主要因子，分别从可见光波段和荧光波段对辐射的贡献出发，发展了海洋水体离水辐射率模式。在卫星水色遥感机理的基础上，同时运用Iqbal，Gordon和Sturm等的大气程辐射模式和太阳耀光模式，使卫星海洋水色遥感的辐射模式系统化，模拟仿真了我国1990年9月3日发射的FYIB卫星两个海洋水色通道的全轨道辐射图像，同时利用从德国柏林大学气象中心接收到的1990年9月23－25日卫星图像进行验证。结果认为，本文所发展的模式可应用于卫星图像质量的预测和水色信息的提取。 相似文献
16.
17.
SPOT5数据东沙环礁珊瑚礁遥感能力分析 总被引：6，自引：0，他引：6
对于大面积的大比例尺珊瑚礁遥感制图而言,SPOT5数据是一种高性价比卫星遥感资料.以Quickbird2数据对东沙环礁珊瑚礁的分类、解译的矢量结果作为该区域实际的珊瑚礁分布,以此为基础分析SPOT5数据的珊瑚礁遥感制图能力.SPOT5只有两个水体穿透信道,从基于光谱数据的分类角度看,以XS1通道为准的珊瑚礁信息提取易将高反射的沙底质归为珊瑚礁;以XS2通道为准的珊瑚礁分布制图存在提取不足问题.由于空间分辨率提高,对潟湖淤泥质中的珊瑚礁提取能力较强,要优于ETM数据.结合ETM数据及PCA融合后的SPOT5的遥感解译结果,能提高SPOT5数据的制图能力. 相似文献
18.
V. M. Kushnir 《Physical Oceanography》2005,15(6):370-382
The comparison of six well-known models of the wave bottom boundary layer shows that they are identical in the case of a smooth
bottom but exhibit serious differences for the other types of conditions. The thickness of the wave bottom boundary layer
and the coefficient of vertical diffusion of momentum are studied by using the relations of the k-ε-model. The validity of these estimates is checked by comparing the measured and computed values of the friction velocity.
This comparison demonstrates fairly good agreement between the results characterized by a coefficient of correlation equal
to 0.851.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 54–67, November–December, 2005. 相似文献