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1.
A procedure is proposed for constructing environmental contours using copula theory. Copulas are functions that define the multivariate probability distribution of a random vector or a set of random variables, and, thus, also determine their dependence structure. Constructing environmental contours requires knowledge of the joint probability distribution of the environmental variables. In many practical applications, the available statistical data is used to estimate the marginal distributions and the linear correlation matrix, and then the Nataf distribution model is employed to obtain the multivariate probability distribution. It turns out that such an approach implies a particular model of dependence structure defined by a Gaussian copula, which might not always be the appropriate one. In this work, some classes of bivariate copulas are considered for modeling the dependence structure of the environmental variables. We examine measures of association, rank-based methods for estimation of copulas, goodness of fit tests for copulas, and copula selection criteria, and apply them to metocean data from hindcasts of tropical storms and extra-tropical events in the Gulf of Mexico. A formulation is proposed for expressing the variates that define the environmental contours as functions of copulas. It is then applied for computing environmental contours of significant wave height, peak spectral period and wind velocity using the estimated copula models. 相似文献
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基于美国国家大气研究中心(NCAR)开发的通用地球系统模式(CESM),本文设计了nudging次表层海温的同化方案,进行了后报实验。对1982-2011年后报结果的分析表明,通过nudging同化,模式对ENSO现象有一定的模拟和预报能力,对赤道太平洋SST、纬向风、降水等海洋、大气要素等的后报结果与GODAS和NCEP再分析资料较接近,可以较好地重现历次厄尔尼诺和拉尼娜事件中异常东传的过程,超前1、3、6个月时,模式预报的Nio3指数与CPC指数的相关性分别达到0.88、0.81、0.70。但模式同时也表现出一定的春季预报障碍,秋季起报的后报效果最好,春季最差。对1982/1983和1997/1999两个厄尔尼诺事件的分析表明,模式后报的纬向风、热通量、风应力等大气变量的响应较实际滞后,而海洋的变化与实际情况相似,这与我们的同化方案设置有关,即模式只同化了次表层海温,进而强迫大气的响应,从而导致大气的变化较滞后。 相似文献
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Real-time wave forecasting using genetic programming 总被引：4，自引：0，他引：4
The forecasting of ocean waves on real-time or online basis is necessary while carrying out any operational activity in the ocean. In order to obtain forecasts that are station-specific a time-series-based approach like stochastic modeling or artificial neural network was attempted by some investigators in the past. This paper presents an application of a relatively new soft computing tool called genetic programming for this purpose. Genetic programming is an extension of genetic algorithm and it is suited to explore dependency between input and output data sets. The wave rider buoy measurements available at two locations in the Gulf of Mexico are analyzed. The forecasts of significant wave heights are made over lead times of 3, 6, 12 and 24 h. The sample size belonged to a period of 15 years and it included an extensive testing period of 5 years. The forecasts made by the approach of genetic programming indicated that it can be regarded as a promising tool for future applications to ocean predictions. 相似文献
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Monitoring pelagic ecosystems using plankton indicators 总被引：2，自引：0，他引：2
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The current lack of high-precision information on subsurface seawater is a constraint in fishery research. Based on Argo temperature and salinity profiles, this study applied the gradient-dependent optimal interpolation to reconstruct daily subsurface oceanic environmental information according to fishery dates and locations. The relationship between subsurface information and matching yellowfin tuna(YFT) in the western and central Pacific Ocean(WCPO) was examined using catch data from January 1... 相似文献
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港口靠船桩工作性状计算的双参数法 总被引：8，自引：0，他引：8
港口靠船桩是承受重复性荷载或多循环荷载的一种横向承载桩。双参数法能较好地描述靠船桩 (单桩、群桩 )的桩土工作性状。用双参数法进行计算时 ,所给的地面条件必须由重复荷载或多循环荷载作用下实测出来。根据现场试桩资料 ,标定桩土参数 ,即k =mx1/n的指数l/n、桩土相对柔度系数α、桩土综合刚度EI等值 ,可以用来设计试桩附近局部地区同类条件下的其它长桩。对于没有进行试桩的某些工程 ,可以联合运用双参数法和p -y曲线法进行桩的分析 相似文献
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Underwater acoustic communications using time reversal 总被引：1，自引：0，他引：1
Edelmann G.F. Song H.C. Kim S. Hodgkiss W.S. Kuperman W.A. Akal T. 《Oceanic Engineering, IEEE Journal of》2005,30(4):852-864
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Sayers C.P. Paul R.P. Whitcomb L.L. Yoerger D.R. 《Oceanic Engineering, IEEE Journal of》1998,23(1):60-71
This paper considers the performance of subsea intervention tasks from an unmanned untethered submersible while using acoustic communications. It is argued that the low bandwidth and high delay imposed by acoustic modems makes it unwise to adopt conventional teleoperation techniques and a system is presented which permits subsea teleoperative tasks to be carried out using such limited communication resources. The described implementation employs active techniques to assist the operator both in performing actions and in recovering from those problems which will inevitably occur during real-world interaction. It provides the operator with both simulated and real visual imagery and is designed to adapt dynamically to changing bandwidth and computational resources. Experiments are described in which an operator in Philadelphia, PA, controlled a robot manipulator mounted on the JASON underwater vehicle submerged off the Massachusetts coast. All communication over this 500-km distance was via a combination of Internet and a simulated acoustic link. Analysis of the bandwidth requirements showed them to be consistent with those from acoustic subsea networks 相似文献
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Refractivity estimation using multiple elevation angles 总被引：1，自引：0，他引：1
Gerstoft P. Rogers L.T. Hodgkiss W.S. Wagner L.J. 《Oceanic Engineering, IEEE Journal of》2003,28(3):513-525
Estimation of the atmospheric refractivity is important for the prediction of radar performance. Surface or elevated trapping layers formed by the outflow of relatively dry and warm air over a cooler body of water often result in the refractive structure-supporting-convergence-zone-like behavior and multimodal effects. The propagation under such conditions can be very sensitive to even small changes in the vertical and horizontal structure of refractivity. Obtaining in situ measurements of sufficient fidelity to estimate where intensifications in the electromagnetic field will occur is difficult. The authors previously have demonstrated the ability to infer refractivity parameters from grazing-incidence radar sea-clutter data. The radar system was the 2.8-GHz space range radar that overlooks the Atlantic Ocean in the vicinity of Wallops Island, VA. The forward modeling consisted of the mapping of an 11-parameter environmental model via an electromagnetic propagation model into the space of the radar clutter observations. A genetic algorithm was employed to optimize the objective function. Ground truth data were atmospheric soundings obtained by a helicopter flying a saw-tooth pattern. The overall result was that the ability to estimate the propagation within the duct itself was comparable to that of in situ measurements. However, the ability to characterize the region above the duct was quite poor. Modern three-dimensional radars, however, have relatively narrow beams. Using these narrow beams at multiple elevations might resolve the ambiguity leading to the poor characterization in the region above the duct. Using radar data from the SPANDAR radar, it is demonstrated that such an approach is feasible and that more-robust estimates can be obtained by using two elevation angles and/or by constraining the solution to contain realistic refractivity profiles. 相似文献
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Ki-Man Kim In-Sic Yang Seung-Yong Chun Won-Tchon Oh 《Oceanic Engineering, IEEE Journal of》2002,27(3):638-641
The passive-range estimation technique using a single focused beamformer has been studied under the sea. However, there are not many more methods in the case of closed multisource environments. In this paper, we propose the technique using dual focused beamformers to estimate the ranges of a closed multisource, and compare the proposed technique with the previous method. The proposed method is verified via computer simulation under the simplified multipath underwater channel model. 相似文献
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海洋内波ADCP监测技术研究 总被引：1，自引：0，他引：1
海洋内波与声场的相互关系是一个十分重要的研究课题.内波是影响声信道特征的重要因素;反之,受内波影响的声场也包含着海洋内波动力过程的信息.针对二者之间的关系,从工程的角度上介绍了利用声学多普勒海流剖面仪(ADCP)对海洋内波进行监测的原理和方法,并结合实际的海试情况给出声学多普勒海流剖面仪对海洋内波的监测结果,验证了方法的有效性. 相似文献
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Quantifying bedform migration using multi-beam sonar 总被引：1，自引：5，他引：1
The migration rates of both medium and very large dunes in a part of the North Sea were determined from high-resolution multi-beam
echo soundings. From the bathymetric maps, crest positions were determined and compared. From changes in the positions of
these crests relative to fixed markers, the migration rates within a tidal cycle and on a seasonal timescale were calculated.
The sediment transport rates derived from the migration of the bedforms compare well with theoretical estimates of the residual
transport in the area. 相似文献
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Wave direction measurements using pitch-roll buoys 总被引：2，自引：0，他引：2
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The impact of rain and spray on the ocean disturbs the sea surface and generates underwater ambient noise. The short scale roughness is influenced by impacting drops due to the momentum transfer. Radar and sonar signals are scattered by the short elements of the sea surface. Spray and rain impact change their characteristics, and consequently affect radar and sonar backscatter. In situ measurements of rain and spray impact are necessary to study their effects on the sea surface. Accurate sea measurements of rain momentum fluxes and drop size distributions are a complex problem, especially on buoys. A new measuring technique has been developed using hydrophones. Exposed to precipitation, these instruments are affected directly by the impact of rain. A drop falling on the hydrophone deforms its surface and is sensed by a piezoelectric transducer. The voltage output of the sensor is a rapidly decaying oscillation. The integral value of this signal is a measure of the drop momentum, and the drop size can be deduced. Laboratory studies of defined drops as well as field measurements of natural rain have shown that hydrophones can be used to determine drop momentums and drop size distributions. Based on simultaneous rain measurements by a Joss-Waldvogel Disdrometer and a hydrophone, an analytical function has been derived which relates drop size and hydrophone voltage output 相似文献
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利用MATLAB实时处理GPS数据 总被引：1，自引：0，他引：1
利用MATLAB软件环境,现场接收并实时处理海上地球物理调查过程中的GPS定位数据,剔除原始数据中的跳点,处理定位误差。采用样条拟合对测线进行拟合光滑,绘制各步处理结果的图形,并将处理前后的航向、航速数据及由此计算出的Eotvos改正值绘制成的曲线进行比较,结果表明:由原始数据计算得到的定位误差较大,与实际船体航行的轨迹有一定差距,而用经过MATLAB处理后的数据计算得到的定位误差较小,航向、航速等与船体航行的真实航迹接近,由此计算出的Eotvos改正值的精度也达到了海上重力测量中Eotvos改正的要求,保证了地球物理数据的质量。 相似文献
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Nikoletta Karaiskou Alexander Triantafyllidis Paula Alvarez Placida Lopes Eva Garcia-Vazquez & Costas Triantaphyllidis 《Marine Ecology》2007,28(4):429-434
Egg identification in plankton samples is usually needed for purposes of stock assessment. Until recently, only morphological characters were used for identifying the eggs of different fish species. Late developmental stages are easily distinguishable due to pigmentation as well as egg and oil globule size range. However, for early stages, these characteristics are difficult to be discriminated and may overlap with other species. European horse mackerel species (Trachurus trachurus, T. mediterraneus, T. picturatus) overlap significantly in their spawning areas in some European waters. Because of the fact that their eggs are morphologically similar, genetic methodologies are needed to identify eggs and larvae to species correctly. In the present study, formalin‐ and ethanol‐preserved eggs were tested to estimate the efficacy of genetic methodologies for species identification of eggs when different preservatives are used. A 370‐bp fragment of cytochrome b was successfully amplified followed by restriction fragment analysis with two restriction enzymes aiming to identify the eggs to species. Horse mackerel egg identification was accomplished with the maximum success in ethanol‐preserved eggs. However, it seems that various preservatives had different effects on the DNA quality of eggs as genetic identification was less successful in formalin‐preserved eggs. Preserving in ethanol a part of the eggs obtained in plankton surveys is suggested for purposes of accurate genetic identification, even if their morphological features are distorted in time. 相似文献
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Forecasting of ocean wave heights, with warning time of a few hours or days, is necessary in planning many operation-related activities in the ocean. Such information is currently derived by numerically solving the differential equation representing wave energy balance. The solution procedure involved is extremely complex and calls for very large amounts of meteorological and oceanographic data. This paper presents a complementary and simple method to make a point forecast of waves in real time sense based on the current observation of waves at a site. It incorporates the technique of neural networks. The network involved is first trained by different algorithms and then used to forecast waves with lead times varying from 3 to 24 h. The results of different training algorithms are compared with each other. The neural output is further compared with the statistical AR models. 相似文献