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1.
南麂岛附近海域潮汐和潮流的特征 总被引：4，自引：2，他引：2
以2008年冬季在浙江近海南麂岛附近投放的4个底锚系观测的水位和流速资料为依据,分析了潮汐和潮流特征。水位谱分析结果显示半日分潮最显著,全日分潮其次;近岸的浅水分潮比离岸大。水位调和分析结果表明:潮汐类型均为正规半日潮,近岸处的平均潮差大于3m,最大可能潮差大于6m,潮汐呈现出显著的低潮日不等和回归潮特征。流速谱分析结果显示半日分潮流最强,全日分潮流其次,且比半日分潮流小得多;近岸浅水分潮流比远离岸显著。流速调和分析结果表明:潮流类型均为正规半日潮流,靠近岸的两个站浅水分潮流较显著;最显著的半日分潮流是M2分潮流,其最大流速介于0.32～0.48m/s之间,全日分潮流均很弱,最大流速小于0.06m/s。M2分潮流均为逆时针旋转,椭圆率越靠近海底越大;最大分潮流流速分布为中上层最大、表层略小、底层最小;最大分潮流流速方向的垂向变化很小,底层比表层略为偏左;最大分潮流流速到达时间随深度的加深而提前,底层比中上层约提前30min。潮流椭圆的垂向分布显示这里的半日分潮流以正压潮流为主;日分潮流则表现出很强的斜压性。 相似文献
2.
An analysis of the radar backscattering from the ocean surface covered by oil spill is presented using a microwave scattering model and Monte-Carlo simulation. In the analysis, a one-dimensional rough sea surface is numerically generated with an ocean waveheight spectrum for a given wind velocity. A two-layered medium is then generated by adding a thin oil layer on the simulated rough sea surface. The electric fields backscattered from the sea surface with two-layered medium are computed with the method of moments (MoM), and the backscattering coefficients are statistically obtained with N independent samples for each oil-spilled surface using the Monte-Carlo technique for various conditions of surface roughness, oil-layer thickness, frequency, polarization and incidence angle. The numerical simulation results are compared with theoretical models for clean sea surfaces and SAR images of an oil-spilled sea surface caused by the Hebei (Hebei province, China) Spirit oil tanker in 2007. Further, conditions for better oil spill extraction are sought by the numerical simulation on the effects of wind speed and oil-layer thickness at different incidence angles on the backscattering coefficients. 相似文献
3.
Purvee Joshi Sandip R. Oza Ujjwal K. Gupta Shailendra Saini D. Ram Rajak I. M. Bahuguna 《Marine Geodesy》2020,43(3):302-323
AbstractIntra and inter-annual variations in the sea ice thickness are highly sensitive indicators of climatic variations undergoing in the earth’s atmosphere and oceans. This paper describes the method of estimating sea ice thickness using radar waveforms data acquired by SARAL/Altika mission during its drifting orbit phase from July 2016 onwards yielding spatially dense data coverage. Based on statistical analysis of return echoes, classification of the surface has been carried out in three different types, viz. floe, lead and mixed. Time delay correction methods were suitably selected and implemented to make corrections in altimetric range measurements and thereby freeboard. By assuming hydrostatic equilibrium, freeboard data were converted into sea ice thickness. Results show that sea ice thickness varies from 4 to 5?m near ice shelves and 1 to 2.5?m in the marginal sea ice regions. Freeboard and sea ice thickness estimates were also validated using NASA’s Operation Ice Bridge (OIB) datasets. Freeboard measurements show very high correlation (0.97) having RMSE of 0.13. Overestimation of approximately 1–2?m observed in the sea ice thickness, which could be attributed to distance between AltiKa footprint and OIB locations. Moreover, sensitivity analysis shows that snow depth and snow density over sea ice play crucial role in the estimation of sea ice thickness. 相似文献
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5.
Coherent reflection of an acoustic plane wave from a random sediment layer over an elastic sea floor
The problem of coherent reflection of an acoustic plane wave from a seabed consisting of a randomly inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis. The random perturbation in the sediment layer is attributable to the sound-speed variations, resulting in volume scattering due to medium inhomogeneities. An approach based upon perturbation theory, combining with a derived Green's function for a slab bounded above and below, respectively, by a fluid and an elastic half-space, is employed to obtain an analytic solution for the coherent field in the sediment layer. A linear system is then constructed to facilitate the computation of the coherent reflection field. The results of the coherent reflection coefficient for various sediment randomness, frequency, sediment thickness, and sea floor elasticity have been numerically generated and analyzed. It is found that the higher/larger the randomness, frequency, thickness, and shear-wave speed, the lower is the coherent reflection. Physical interpretations for the characteristics of the various results are provided. 相似文献
6.
Suguru Ohta 《Journal of Oceanography》1985,41(2):121-133
A peculiar swimming holothurian referable toEnypniastes eximia Theel, of the family Pelagothuriidae was photographed frequently on the continental slopes within Suruga Bay and Sagami Bay. The holothurians of this family are gelatinous, medusa-like creatures with a specific gravity nearly equal to that of seawater, and they have been thought to live a pelagic life. Of the 35 individuals in the bottom photographs taken near the bottom, 26 individuals (74.3 %) were swimming, 1 (2.9 %) was just landing on the bottom and 8 (22.8 %) were walking on the sea floor. Correction for the pyramidal shape of the camera's field of view suggests that 90 % of the population was swimming within several meters of the bottom, and 10 % was on the sea floor. When swimming, 12 antero-dorsal appendages, inter-connected by webe to form a velum as in the elpidiid holothurianPeniagone, are either folded anteriorly in a circle or opened posteriorly like an umbrella. Propulsion seems to be accomplished by metachronal fanning of the posterior webbed podia and by undulatory movement of the antero-dorsal veil-like structure. The latter might also function as a parachute or stabilizer in descending. When on the sea floor, the holothurian always faces downstream with the velum stretched forward, while the aspidochirote tentacles, which are folded in swimming, are pressed on the sediment surface. In addition, this organism leaves trails and constricted fecal strings on the sediment. These observations suggest thatE. eximia does not ingest food in midwater, but, rather feeds selectively on the surface deposits of the sea floor. Although the holothurian has lost the ability to walk effectively on the sea floor by podia, it may utilize the swifter bottom current above the turbulent Ekman layer for locomotion and dispersal. 相似文献
7.
Abstract Sampling of submarine sediments by an improved piston corer and a bucket dredger has been carried out since 1973. The length of the core samples ranged from 0.9 m to 5.4 m. The recovery ratio ranged from 39.1 percent to 98.9 percent. The physical and engineering properties of 16 sediment cores and the physical properties of 125 dredged samples were determined, and variation of these properties was analyzed. Clayey silts and silty clays cover the floor of relatively wide bays and sea areas. Sands and sandy silts blanket the floor of channels that have swift currents, and are also found in the vicinity of estuaries. The piston core samples showed considerable sample disturbance, which should be estimated quantitatively in the future. 相似文献
8.
S. Ramesh K. Nvv Murthy S. M. Hussain S. Ramasamy G. A. Ramadass 《Marine Georesources & Geotechnology》2020,38(1):57-63
AbstractPalar basin is located between Pennar and Cauvery sedimentary basins of East coast of India in Bay of Bengal, northeast Indian Ocean. Sea floor drill (Wire-line Autonomous Coring System – WACS) with operational capability of up to 3000?m water depth was developed to collect long cores from deep sea floor for geotechnical and ocean resource assessment studies. During the drilling operation it encountered Nummulitic coralline limestone of Lower Eocene age at 18 meters below the seafloor (mbsf) at 850?m water depth indicating carbonated platform presence for the first time at the study region. Bathymetry contour from Naval Hydrography Chart and General Bathymetric Chart of the Oceans (GEBCO) has revealed the presence of shallow mounds from 50 to 200?m depth closure contour near the sampling site at 850?m water depth which might be a submerged carbonated structure. Since, Nummulites are shallow water dwelling fauna (<20?m depth) but its occurrence at 18 mbsf in 850?m water depth is recorded because of the advancement in technology tool for long core sampling by means of sea floor drill. 相似文献
9.
Based on the non-dimensional general function for the thermal structure features presented by S. A. Kitaigorodsky et al. (1963, 1965)[10,11]. this paper tries to establish semi-empirical and semi-theoretical models bfor the thickness of the upper homogeneous layer of the ocean, thermocline intensity and lower oundary depth of thermocline by consecutive observations from 159 stations in the Bohai Sea,Huanghai Sea and East China Sea in the warm half of the years from 1957 to 1964 and the heat budget at the sea surface computed with the simplified computing formulae proposed by Wang (1983)[22]. This model indicates the main factors forming the thermal structure features in the upper layer of the ocean and their function. With the model, one can directly use the sea surface temperature, air temperature and wind speed to compute the thermal feature in the upper layer of the ocean. 相似文献
10.
A novel variation of the geophysical technique known as MOSES, for Magnetometric Off-Shore Electrical Sounding, has been developed to map the electrical properties of the sea floor in Aretic regions. The particular target is the permafrost layer under the Beaufort Sea, a layer containing frozen or partially frozen sediment from 100 to 600 m thick underlying shallow sea water, typically 10 to 100 m deep, and several tens of metres of soft sediment. A detailed knowledge of the location and physical properties of the permafrost layer is essential for accurate interpretation of reflection seismic data. The permafrost can contain pockets, regions or layers of gas hydrate. The latter is both a possible resource and a hazard to drilling operations or hydrocarbon production. A local map of the permafrost zone is essential geotechnical information required prior to the construction of an offshore structure or pipeline.The MOSES method is particularly suitable for offshore electrical mapping as it can be made relatively insensitive to the shielding effects of the highly conductive sea water, in sharp contrast to many other electrical techniques. The transmitter is a vertical, long-wire bipole, extending from the sea surface to the sea floor. A commutated current is fed to two large electrodes: one near the sea surface and the other on the sea floor. The return current is through the sea water and the subjacent sediment. The receiver consists of two horizontal orthogonal coils located on the sea floor, and the data are measurements of two components of the magnetic field as a function of frequency and transmitter-receiver horizontal separation.The electrical conductivity of a sample of frozen material is much smaller than that of unfrozen or partially frozen sediment of the same type. Frozen and unfrozen thin layers are often observed sequentially throughout the geological section. The resistivity measured as a function of depth by an electrical logging tool is consequently highly variable. The resulting depth-averaged resistivity, the resistivity resolved by a surface electrical method, is macro-an-isotropic. An experimental design study reveals that both the vertical and horizontal averaged resistivities could be determined in a MOSES sounding without vertical scale distortion.A test of the methodology in very shallow water was conducted in the spring of 1986 at a site, approximate coordinates (70° N, 134.5° W), 85 km north-west of the town of Tuktoyaktuk. The instrumentation was lowered and subsequently recovered through holes in the ice which covers the Beaufort Sea at that time of the year. The transmitter power was obtained from a single lead-acid battery. Transmitter-receiver separations ranged from 10 to 300 m. A rapid increase in sediment resistivity with depth was observed. The higher resistivity values are consistent with those expected for a partially frozen zone. 相似文献
11.
Yiguo Xue Binghua Zhou Daohong Qiu Maoxin Su Chuanqi Qu Xueliang Zhang 《Marine Georesources & Geotechnology》2013,31(10):1267-1276
AbstractThe overlying rock thickness of a subsea tunnel controls its vertical line. It not only ensures the safety and stability of tunnel construction period and operation period, but also ensures the economy of subsea tunnel. In the current research, few papers give full consideration to the complex indicators of prediction the overlying rock thickness. However, in this study, a hybrid intelligent system was established to predict the overlying rock thickness of a subsea tunnel based on Qingdao Kiaochow Bay Subsea Tunnel, China. The sea depth, basic quality index of rock mass, soft soil layer thickness, permeability coefficient, and construction management level were selected as the main factors influencing the overlying rock thickness. Using the data obtained from project site exploration, objective weight factors were calculated using rough set theory, and subjective weight factors were calculated using the analytic hierarchy process. Furthermore, the combination of weights was obtained for each factor. Finally, the weight of influencing factors was incorporated into the extension model, and the overlying rock thickness of pending section was calculated. The results of overlying rock thickness prediction model are consistent with the actual value, indicating that the model has good engineering applicability and application value. 相似文献
12.
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13.
《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(7):1272-1283
A novel autonomous free-fall lander vehicle, with a capability down to 6000 m, was deployed off Cape Verde for studies on bioluminescence in the deep sea. The system was equipped with a high-sensitivity Intensified Silicon Intensified Target (ISIT) video camera, a programmable control-recording unit and an acoustic current meter with depth and temperature sensors. The ISIT lander was used in three modes: (1) free falling at 34 m min−1, with the camera looking downwards at a mesh screen, recording impacts of luminescent organisms to obtain a vertical profile down to the abyssal sea floor, sampling at >100 l s−1; (2) rotating, with the lander on the sea floor and the camera orienting to the bottom current using a servo-controlled turntable, impacts of luminescent organisms carried by the bottom current onto a mesh screen mounted 0.5 m in front of the camera were recorded to estimate abundance in the benthic boundary layer; (3) baited, with the camera focused on a bait placed on the sea floor.Profiles recorded abundance of luminescent organisms as 26.7 m−3 at 500–999 m depth, decreasing to 1.6 m−3 at 2000–2499 m and 0.5 m−3 between 2500 m and the sea floor at 4046 m, with no further detectable significant change with depth. Rotator measurements at a 0.5 m height above the sea floor gave a mean abundance of 0.47 m−3 in the benthic boundary layer at 4046 m and of 2.04 m−3 at 3200 m. Thirty five minutes after the bait was placed on the sea floor at 3200 m, bioluminescent fauna apparently arrived at the bait and produced luminescent displays at a rate of 2 min−1. Moving, flashing light sources were observed and luminescent material was released into the bottom current. 相似文献
14.
以非夏眠期刺参(Apostichopus japonicus)为对照组,在刺参夏眠不同程度选取3个时间点,将其分为夏眠初期、深度夏眠期、夏眠解除期3个阶段,采集前肠组织为研究材料,制作石蜡切片,统计不同时期刺参前肠壁厚度、前肠黏膜上皮、黏膜下层、肌肉层和外膜的厚度及直径.结果显示,与对照组相比,夏眠不同时期黏膜下层厚度均无差异(P＞0.05),夏眠初期黏膜上皮和外膜显著薄于对照组(P＜0.05),深度夏眠期黏膜上皮和肌肉层显著薄于对照组(P＜0.01),刺参前肠直径在深度夏眠期显著变小(P＜0.01).计算前肠各组织层占肠壁厚度的比例发现:夏眠初期黏膜上皮和外膜厚度占肠壁总厚度的比例要显著小于非夏眠期(P＜0.05),黏膜下层的比例则显著变大(P＜0.01),肌肉层所占比例在深度夏眠期显著小于其他几个时期(P＜0.05). 相似文献
15.
Kisaburo Nakata 《Journal of Oceanography》1981,37(2):94-98
Current meter data from various depths near the sea bottom collected for 31 days at time intervals of 10 minutes using a subsurface buoy system at a depth at 38 m on the continental shelf off Akita, Japan have been analyzed. The results show the existence of a stationary Ekman layer. The typical range of the characteristic parameters are estimated as follows; friction velocity: 0.38 cm s–1; Ekman layer thickness: 16 m; logarithmic layer thickness: 4 m–6 m; constant flux layer thickness: 0.4–0.6 m; Ekman veering: 28.7°; drag coefficient: 0.24×10–2–0.53×10–2. Veering was also observed in the logarithmic layer. 相似文献
16.
A newly developed towed transient electromagnetic (TEM) system is capable of measuring the electrical conductivity of the
uppermost 5–10 m of sediments on the sea floor. The profiles of conductivity may be interpreted to give the porosity and likely
texture of the bottom sediments. Recent tests of the system have demonstrated that data may be collected continuously in a
surveying mode. Results from Knight Inlet, British Columbia, are in good agreement with sea floor samples from the area.
Applications for the system include the rapid identification of sediment types for dredging operations, geotechnical surveys,
or reconnaissance mapping of Quaternary geology. 相似文献
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18.
Theo Engelis 《Marine Geodesy》2013,36(1):45-69
Abstract A set of time‐averaged sea surface heights at 1° intervals, derived from the adjusted SEASAT altimeter data, and the GEML2 gravity field are used to estimate the long‐wavelength stationary sea surface topography. In order to reduce the leakage of energy in the estimated sea surface topography, the GEML2 field is augmented by the Rapp81 gravity field to generate geoidal undulations with wavelengths consistent with the ones of sea surface heights. These undulations are subtracted from the sea surface heights, and the resulting differences are subjected to filtering in order to recover sea surface topography with minimum wavelengths of 6000 km and an estimated accuracy of 20–25 cm. These estimates agree well with oceanographic and other satellite‐derived results. The direction of current flow can be computed on a global basis using the spherical harmonic expansion of sea surface topography. This is done not only for the SEASAT/GEML2 estimates, but also using the recent dynamic topography estimates of Levitus. The results of the two solutions are very similar and agree well with the major circulation features of the oceans. 相似文献
19.
Peter John Schultheiss 《Marine Georesources & Geotechnology》2013,31(4):343-367
Abstract Foundations for offshore structures present a design problem resulting from two primary sources. First, the normally consolidated sea‐floor sediments are often weak and compressible compared to relatively competent terrestrial soils. Second, the technical difficulties of either obtaining relatively undisturbed sea‐floor samples or of performing in situ mechanical tests can be more problematic than with terrestrial soils. Any technique that might improve the assessment of sediment behavior is worthy of investigation. This paper describes some preliminary experiments which measure P and S velocities during conventional soil testing procedures. Computed static and dynamic moduli, measured from tests with different strain levels, have been compared, revealing that although two orders of magnitude separate the moduli, there are similarities in the way certain moduli change with increasing stress levels. It is suggested that the use of a “frame‐wave”; velocity in the calculation of dynamic moduli may reduce drastically the differences that exist between the static and dynamic moduli for saturated sediments. In this way it is thought that results from tests, such as those described in this paper, not only provide empirical correlative data for a given sediment, but may also contribute to a clearer understanding of its behavior under loading conditions. 相似文献
20.
According to the exploration contract about polymetallic sulfides in the SWIR （Southwest Indian Ridge） signed by China with the International Seabed Authority, to delineate sulfide minerals and estimate resource quantity are urgent tasks. We independently developed our first coincident loop Transient Electromagnetic Method （TEM） device in 2010, and gained the TEM data for seafloor sulfide at South Atlantic Ridge 13.2°S in June 2011. In contrast with the widely applied CSEM （Marine controlled-source electromagnetic） method, whose goal is to explore hydrocarbons （oil/gas） of higher resistivity than seawater from 102 to 103 m below the sea floor, the TEM is for low resistivity minerals, and the target depth is from 0 to 100 m below the sea floor. Based on the development of complex sulfide geoelectrial models, this paper analyzed the TEM data obtained, proposing a new method for seafloor sulfide detection. We present the preliminary trial results, in the form of apparent resistivity sections for both half-space and full-space conditions. The results cor- respond well with the observations of the actual hydrothermal vent area, and the detection depth reached 50-100m below the bed, which verified the capability of the equipment. 相似文献