Aliasing due to sampling of the Adriatic temperature, salinity and density in space     

Zoran Pasari&#x;  Mirko Orli&#x;  Craig M. Lee 《Estuarine, Coastal and Shelf Science》2006,69(3-4):636

High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m³ (0.25 °C, 0.10 and 0.05 kg/m³) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m³ (0.93 °C, 0.25 and 0.22 kg/m³) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region.  相似文献   

Estimation of Sea Ice Thickness from SARAL/AltiKa in Drifting Orbit Phase     

Purvee Joshi  Sandip R. Oza  Ujjwal K. Gupta  Shailendra Saini  D. Ram Rajak  I. M. Bahuguna 《Marine Geodesy》2020,43(3):302-323

Abstract

Intra 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   

Target strength of the lanternfish, Stenobrachius leucopsarus (family Myctophidae), a fish without an airbladder, measured in the Bering Sea   总被引：1，自引：0，他引：1  

Yasuma  Hiroki; Takao  Yoshimi; Sawada  Kouichi; Miyashita  Kazushi; Aoki  Ichiro 《ICES Journal of Marine Science》2006,63(4):683-692

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Distribution of nonlinear wave crests     

J. Al-Humoud  M. A. Tayfun  H. Askar 《Ocean Engineering》2002,29(15):1929-1943

The distribution of nonlinear wave crests is examined on the basis of a theoretical probability density previously given elsewhere (J. Eng. Mech. 120 (1994) 1009). Certain errors contained in the original theoretical density are corrected, and the corresponding exceedance distribution is derived. The resulting theoretical forms of the probability density and exceedance distribution are then slightly simplified and compared with nonlinear wave data gathered under hurricane conditions. The results indicate that the proposed theoretical forms describe the observed distributions of large wave crests better than the Rayleigh law. However, the quantitative accuracy of the predictions is somewhat poor, as is typical of approximate theories based on Gram–Charlier-type expansions.  相似文献   

流形上的空间密度聚类算法研究     

刘峰  刘希玉  刘弘 《中国海洋大学学报(自然科学版)》2007,37(4):681-684,626

研究流形上的聚类分析，针对基于密度的空间聚类引入了流形概念，提出1种基于流形的密度聚类算法，该方法将流形的概念与聚类相结合，可以适用于样本为复杂分布的聚类。文中通过实例证明此算法的有效性。  相似文献   

Effects of sediment properties on surface-generated ambient noise in a shallow ocean     

Jin-Yuan Liu  I-Chun Lin 《Ocean Engineering》2005,32(16):1887-1905

Surface-generalized ambient noise in a shallow ocean waveguide with a sediment layer possessing a specific class of density and sound speed distributions capable of describing a realistic seabed environment is considered in this analysis. This class of non-uniform sediment layer has the density and sound speed distributions varying with respect to depth as a generalized-exponential and an inverse-square function, respectively. The study invokes a formulation developed by Kuperman and Ingenito (Kuperman, W. A., Ingenito, F., 1980. Spatial correlation of surface-generated noise in a stratified ocean. J. Acoust. Soc. Am., 67, 1988-1996.) for surface noise generation, in conjunction with the analytical solutions for the Helmholtz equation corresponding to the sediment layer, to arrive at an analytical expression convenient for numerical implementation. The intensity and spatial correlation of the noise sound field are analyzed with respect to the variation of the system parameters, including frequency, sediment layer thickness, sound speed gradient, with emphasis on the effects of sediment properties on the ambient noise field. The results have demonstrated that the intensity of the noise field is relatively sensitive to the variation of the parameters, but the spatial correlation is affected to a less extent, suggesting that the energy distribution, rather than the spatial structure, of the noise field is more susceptible to the environmental variations.  相似文献   

Acoustic plane-wave scattering from a rough surface over a random fluid medium     

Jin-Yuan Liu  Chen-Fen Huang  Ping-Chang Hsueh 《Ocean Engineering》2002,29(8):915-930

Acoustic plane-wave scattering from a rough surface overlying a fluid half-space with a sound-speed distribution subject to a small random variation is considered. Under the assumption that the surface roughness and medium randomness are statistically independent, the scattered field may be derived by first solving for the mean field in the medium, and then incorporating with boundary-perturbation method to obtain the total mean field and the power spectral density of the scattered field. The employed algorithm is compatible to the analysis available in the existing literature so that the formulations are conveniently integrated. The results for the power spectral density have shown that the effects of medium inhomogeneities on the rough surface scattering are limited in a spectral regime where the scattered components have shallow grazing angles. The distribution of the power spectral density over the space is primarily governed by the power spectrum and correlation lengths of the rough surface.  相似文献   

16米风化砂回填地基的深层振密加固     

曹永琅  张光蒲  丛健 《海岸工程》2001,20(4):21-26

结合北方某重力式深水 ( -1 6.0 m)码头沉箱后壁 1 4.5 m范围的回填风化砂经深层振密处理这一工程实例 ,介绍了回填砂振密的技术要求、施工工艺和方法及振密效果的检测。同时对施工与检测中的某些技术问题提出了自己的看法。  相似文献   

悬对沙Mellor-Yamada海洋边界层模型计算结果的影响     

李华军  梁丙臣  李东永  李磊岩 《海洋科学》2004,28(1):27-32

为了分析海洋水体垂向水流紊动及紊动交换情况而采用了一维的海洋边界层模型(Mellor-Yamada)并利用数值实验的方法对悬沙、盐度、温度等数据进行分析。原模型未将悬沙考虑在内，本文试将它引入进去探讨由于它的存在对紊动混合特性的影响。2000年4月，Mellor将最初的模型引入了依赖于Richardson数的紊动动能耗散率。本文通过比较具有悬沙和不具有悬沙两种情况下的速度、温度和盐度垂向分布随时间的变化，分析讨论由于悬沙的存在所引发的密度层化对紊动混合作用的影响，并发现悬浮泥沙抑制了部分模拟时间的紊动混合作用。  相似文献   

北部湾三维风生流及密度流模拟   总被引：16，自引：0，他引：16  

夏华永  李树华  侍茂崇 《海洋学报》2001,23(6):11-23

将Casulli差分格式引入三维物理海洋模型计算，模拟了北部湾风生流及密度流。模拟结果表明，夏季西南季风在北部湾导致一个顺时针环流，夏季海水密度梯度导致一个逆时针方向的环流，密度流明显强于风生流；冬季东北寒潮导致一个逆时针环流。模拟结果不支持北部湾夏季为一顺时针环流、冬季为逆时针环流的传统结论，而支持终年为逆时针环流的观点。  相似文献