共查询到20条相似文献，搜索用时 15 毫秒
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- The spectral form of wind waves is investigated based on the ocean wave data observed at three nearshore stations of Taiwan. In this study, the generalized forms of Pierson-Moskowitz spectrum and JONSWAP spectrum are used to describe the local wave spectrum by selecting suitable spectral form parameters. It is shown that, at a specific site, the similarity of wave spectral form exists. Thus it is possible to use a representative spectral form for a given nearshore region to describe the wave spectrum at this nearshore. On the other hand, the effects of relative water depth on spectral form are examined. The feasibility of two spectral models in finite water depth is evaluated by using the same field wave data. 相似文献
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针对机载合成孔径雷达(SAR)对海探测特点,采用多入射角法从SAR数据本身得到与海浪参数反演区域时空匹配的同步海面风速和风向,并结合线性变换关系,计算得到海浪初猜谱对应的仿真SAR图像谱,将仿真SAR图像谱和观测SAR图像谱输入代价函数中进行迭代运算,通过非线性方程的解算得到最适海浪谱;采用交叉谱法去除海浪传播180°方向模糊,最终得到海浪参数。论文提出的基于同步风场的机载SAR海浪参数反演方法,充分利用了机载SAR海洋环境探测的优势,解决了传统SAR海浪参数反演中初猜谱构造依赖外部风场的问题,机载同步飞行试验的海浪参数反演结果与浮标观测值的有效波高、波向的均方根误差分别为0.23 m和13.23°,验证了该方法的有效性,可为机载SAR海浪参数反演业务化提供支持。 相似文献
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《Oceanic Engineering, IEEE Journal of》2009,34(3):250-261
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针对水下航行器在二维信号场中的场源搜索问题,提出了一种基于径向基函数神经网络（radial basis function neural network,简称RBFNN）的在线自主寻源算法。在神经网络中引入全局正则化参数以保证泛化性和稳定性,通过最小化广义交叉验证误差（generalized cross-validation,简称GCV）进行正则化参数的迭代优化,并利用增量式奇异值分解（incremental SVD）对迭代过程进行加速,此外通过基于样本新颖性的资源分配网络算法（resource-allocating network,简称RAN）进行径向基函数的分配,在此基础上使用动量梯度算法进行航行器运动方向的规划。最后,以热泉区硫化氢浓度分布场中的搜索作业为背景,使用该算法与其他研究中的算法进行单峰值信号场的场源搜索模拟计算对比,结果显示该算法对于信号场梯度的估计更加准确,且搜索过程的路径更短。此外在多峰值信号场的寻源模拟中该算法能够以较高的成功率通过局部最大值区域。证明该算法具有良好的拟合、预测性能以及稳定性,并且能在一定程度上避免陷入局部最优解。 相似文献
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《Coastal Engineering》2006,53(11):915-927
A set of empirical formulations is derived that describe important wave properties in shallow water as functions of commonly used parameters such as wave height, wave period, local water depth and local bed slope. These wave properties include time varying near-bed orbital velocities and statistical properties such as the distribution of wave height and wave period. Empirical expressions of characteristic wave parameters are derived on the basis of extensive analysis of field data using recently developed evolutionary algorithms. The field data covered a wide range of wave conditions, though there were few conditions with wave periods greater than 15 s. Comparison with field measurements showed good agreement both on a time scale of a single wave period as well as time averaged velocity moments. 相似文献
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土壤湿度是潮滩湿地生态环境的重要参数之一。以长江口南汇潮滩为研究区,利用2005年5月2日和3日2景时序相近、低入射角HH极化的ENVISAT ASAR数据,在数据预处理的基础上,进行了入射角归一化处理,然后采用Zribi-Dechambre模型计算了南汇潮滩土壤粗糙度和土壤湿度。其土壤粗糙度分布范同为0.05～0.8 cm,土壤湿度分布范围为1%～3.8%。最后,采用上海地质调查研究院土壤湿度实测数据进行了验证,其均方根误差为3.62%,表明该方法对合成孔径雷达影像进行土壤湿度信息的提取有较好的适用性。 相似文献
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A. Ya. Matveev A. A. Kubryakov A. G. Boev D. M. Bychkov V. K. Ivanov S. V. Stanichny V. N. Tsymbal 《Izvestiya Atmospheric and Oceanic Physics》2016,52(9):940-950
The possibilities of a multiangle method of radar diagnostics to determine thickness of an oil film on a sea surface by comparing the radar data with the quantitative modeling results obtained using the model of oil spreading dynamics are analyzed. The experimental results of the remote sensing of the Caspian Sea water area near the Neftyanye Kamni oil field by the Envisat-1 synthetic aperture radar (SAR) and the new Floating Objects Tracking System (FOTS) model of oil spreading are used for the analysis. The model allows to calculate the dynamics and change in the mass and size of an oil slick basing only on the available data of satellite measurements and atmospheric reanalysis.The model takes into account the main processes that influence the slick formation (gravity spreading, advective transport, dispersion, emulsification, turbulent mixing, and evaporation). This model is used to calculate the thickness evolution and dynamics of the displacement of oil slicks in the period between two consecutive radar images of this region (0.5–4 days) and to estimate the volumes of oil spilled in the field. The good consistence of the height of the oil film calculated using radar measurements and the modeling results confirms the method’s reliability. 相似文献
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江苏梁垛闸潮间带表层沉积物特征及输运趋势 总被引：3，自引：0，他引：3
采用激光粒度仪对2004年1月在江苏梁垛闸附近潮间带下部采集的36个表层沉积物样品以及垂向海岸的8个表层沉积物样品进行了粒度分析,获得了粒径分布和矩值参数的分布规律,结果表明:(1)江苏梁垛闸附近潮间带表层沉积物以粉砂为主,随着由海向陆水动力的减弱,沉积物粒度参数出现有规律的变化,由海向岸其粒径逐渐变细,分选变好,砂的含量逐渐减少,粘土和粉砂的含量逐渐增多。(2)运用G ao-Co llins二维沉积物粒径趋势分析模型模拟出了江苏梁垛闸潮间带的泥沙输运趋势,即该区的泥沙主要向北和北偏东16°左右方向输运,这种运动趋势主要受当地的潮流特征、地貌形态等因素的控制。 相似文献
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In September 1988, a series of acoustic propagation experiments were conducted in the Hudson Canyon area. These included synthetic aperture experiments in which a source transmitting a set of four pure tones was towed toward/away from a vertical array of 24 receivers. Data obtained at 50 Hz during one of the synthetic aperture experiments are used to obtain a model for the compressional wave speed profile in the bottom using a modal inverse method. This model is further refined using 175 Hz data. The ability of the inferred model to predict the field at 50 Hz and higher frequencies is examined 相似文献
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厦门胡里山西侧海滩沉积物粒度特征分析 总被引：2，自引：3，他引：2
研究区海滩沉积物的粒度分析结果显示，（１）该区海滩中潮位线一带浅表层物质主要由粗砂至细砾级的颗粒组成，平均粒径为－０．１φ。粒度组成上有２－３个次组分，各组分的众数位分别平均为－１．２、０．４和２．５φ。（２）概率值累积曲线的各段呈“陡－缓－陡”的排布模式，与Ｖｉｓｈｅｒ的海滩沉积物的典型模式不同。 相似文献
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在讨论了MODIS中分辨率成像光谱仪(Moderate Resolution Imaging Spectroradiometer)遥感图像几何畸变的成因后,文章引入了利用MODIS数据间的互补性去除这种"双眼皮"现象的概念,其后采用了Kriging插值的方法对数据进行重采样.在与其他几何纠正和插值方法进行比对后结果表明,该方法能较好地去除边缘重叠影响,并能保持原有云图的特征和信息,对MODIS资料数据在后续的反演工作中有一定意义. 相似文献
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This paper presents an adaptive hybrid algorithm to invert ocean acoustic field measurements for seabed geoacoustic parameters. The inversion combines a global search (simulated annealing) and a local method (downhill simplex), employing an adaptive approach to control the trade off between random variation and gradient-based information in the inversion. The result is an efficient and effective algorithm that successfully navigates challenging parameter spaces including large numbers of local minima, strongly correlated parameters, and a wide range of parameter sensitivities. The algorithm is applied to a set of benchmark test cases, which includes inversion of simulated measurements with and without noise, and cases where the model parameterization is known and where the parameterization most be determined as part of the inversion. For accurate data, the adaptive inversion often produces a model with a Bartlett mismatch lower than the numerical error of the propagation model used to compute the replica fields. For noisy synthetic data, the inversion produces a model with a mismatch that is lower than that for the true parameters. Comparison with previous inversions indicates that the adaptive hybrid method provides the best results to date for the benchmark cases 相似文献
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综合国内外现有研究成果,分析了桩周流场结构及局部冲刷坑的分布形态,通过三维数值模拟,验证了局部冲刷最大值点出现在桩前,且冲坑坡度近似等于泥沙水下休止角的结论。从国内外规范内局部冲深计算公式中筛选出跨海桥梁钢管桩局部冲刷深度的主要影响因素。基于能量平衡理论,通过来流水流搬运冲刷坑内泥沙过程中的能量守恒,推导了概念清晰、形式简单的局部冲刷深度预测公式。区别于现有多数公式主体结构,该公式为关于局部冲深的一元三次方程,通过水下泥沙休止角来考虑泥沙对冲刷的影响以及冲刷过程中冲刷坑自身深度及范围变化对冲刷产生的影响。利用最小二乘法,结合环杭州湾区域三座跨海大桥的试验及实测数据拟合确定了公式相关参数,并与国内外规范内的公式对比验证,结果表明,该公式精度较高,可为实际工程计算分析提供参考。 相似文献
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The current methods used in world practice for the determination of the basic parameters of the vital functions of bacterioplankton
(the number, biomass, and production) are discussed. While comparing the different methods and their modifications, the peculiarities
of their application for particular natural or laboratory environments are emphasized. The specificity of applying different
microbiological methods for field research is examined. When choosing the methodological base for describing the characteristics
of a bacterial community, one should proceed from the specific problem facing the researcher. In the case of routine monitoring,
the following techniques are convenient and widely used: direct counts of DAPI fluorochrome-stained bacteria using a fluorescence
microscope; the calculation of the biomass of the microorganisms on the basis of the relationship between the cell’s mass
and its size; the estimation of the bacteria production via labeled leucine incorporation. 相似文献
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一维综合孔径微波辐射计能够有效提高观测的空间分辨率,其观测入射角通常在0°~55°范围内变化。为了开发适用于一维综合孔径微波辐射计的海面温度反演算法,需要评估其观测亮温对海洋大气环境要素的敏感性。利用海面发射率模型和大气辐射传输模型,构建了适用于一维综合孔径微波辐射计的微波海洋大气辐射传输模式,研究了C波段垂直和水平极化微波辐射亮温在不同入射角下对海洋大气环境要素的敏感性变化情况,并定量计算了相应的敏感系数。结果表明:垂直和水平极化亮温对海洋大气环境要素的敏感性表现出不同的特性。随着入射角的增大,垂直极化亮温对海面温度的敏感性增强,对海面风场的敏感性相对减弱;水平极化亮温则相反。由大气水汽含量和云液态水含量误差引入的垂直和水平极化亮温误差随入射角增大而增大,但是,即使在55°的大入射角下垂直和水平极化亮温误差仍小于0.12 K。对于海面温度反演精度优于1 K的要求,一维综合孔径微波辐射计的测温精度需优于0.6 K。研究结果对于一维综合孔径微波辐射计海面温度反演算法的研究和载荷设计具有一定的理论指导意义。 相似文献
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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