基于变系数Gardner方程的海洋内波研究

本文主要是基于同时含有二阶和三阶非线性项的变系数Gardner方程对海洋内孤立波的传播特性开展研究。在吕宋海峡海域,展示了下降型海洋内波的传播特性及其在SAR图像上的信号特征,并着重分析讨论了耗散项和微扰项对海洋内波所引起的表层流速变化的影响。     

The validity of the composite surface model and its applications to the modulation of radar backscatter

Abstract

The composite surface model is compared with the Kirchoff method and shown to be equivalent for radar backscatter at moderate incidence angles in most commonly occurring sea states. Based on this comparison, limits are determined for the validity of the composite surface model. The model is then utilized to study the modulation of the radar cross-section of the ocean surface by long surface waves and internal waves. It is shown that apart from the well understood tilt modulation and the direct hydrodynamic modulation of the short waves, there is also an additional indirect modulation of the radar cross-section due to the hydrodynamic modulation of the intermediate waves by the long waves. Computer simulations are used to investigae these modulation mechanisms for different sea states, incidence angles and radar frequencies. It is shown that this modulation is strongest at small incidence angles and high radar frequencies. The simulations show that internal waves may be observed by X-band and Ka-band radars due to the indirect modulation through the intermediate waves. It is also shown that, contrary to previous predictions, the indirect modulation process results in modulation of radar backscatter by surface waves that travel normal to the radar look direction.     

Signatures of resonant and non-resonant scattering mechanisms on radar images of internal waves

The results of two polarization airborne radar imagery tests of the ocean surface obtained during the JUSREX'92 experiment are presented. It is shown that the traditional composite surface model with small-scale 'Bragg' waves superposed over larger gravity waves can not explain either the contrasts of internal wave surface manifestations in conditions of a stable atmospheric boundary layer at low grazing angles (LGA), or the apparent difference between the images obtained at different polarizations in unstable atmospheric conditions. We attribute this discrepancy to the presence of mesoscale steep waves, which produce non-resonant scattering and make different relative contributions to the total cross sections for the two polarizations. The possibility of distinguishing between surface manifestations of atmospheric and oceanic origin is also discussed.     

Fast prediction of hydration free energies from molecular interaction fields.

A novel empirical model is presented that allows the fast computation of hydration free energies with high accuracy. The linear model is based upon the separation of the free energy of hydration into a cavity and an interaction term. The cavity contribution is modeled as a linear combination of molecular volume and surface terms. The interaction part is derived from the statistical three-dimensional (3D) free energy density and is modeled approximately as a molecular interaction field using the program GRID. A compression scheme is employed to represent this 3D information on the molecular surface by means of a linear combination of surface functions. A set of 81 small organic molecules with known experimental hydration free energies is used to determine the coefficients of the linear model by least squares regression. The fit is statistically significant yielding a correlation coefficient of 0.99, a root mean square error of 0.27 kcal/mol for the 81 molecules belonging to the training set, and 0.63 kcal/mol for an independent test set of 10 molecules.     

Adaptive smoothness based robust active contours

Active contours are a popular class of variational models used in computer vision for tracking and segmentation. The variational model consists of a data-fitting and a regularisation term. Depending on the data-fitting term, active contour models are classified as either gradient or region based models. An often overlooked but crucial aspect of these models is that these two terms are weighted by a manually set constant weight. This constant weight often leads to incorrect segmentation, particularly for gradient based energies. This failure rate is high in the presence of strong gradients nearby the target or when the object gradient is not uniformly strong. In such circumstances, setting the weight becomes a critical and often unsatisfying task. In this work, we propose a new spatially varying and dynamic curve evolution term for robust segmentation of gradient based models. In contrast to the majority of the existing work in literature which focuses on defining new data-fitting terms, the evolution term proposed here is related to the regularisation of evolution. The intuition here is that in images although object boundaries are generally continuous, the magnitude of the gradient map so generated is not uniformly strong. Therefore, any energy formulation which fixes the weights of the data-fitting and regularisation term will run into the problems mentioned above. In this work, we propose an energy term which defines the regularisation term in a spatially varying manner. The advantage of this term is that it is independent of the image based data-fitting energy term and hence can be plugged into the vast variety of the existing gradient based active contour models.     

基于卫星影像的自动提取中尺度漩涡方法研究

中尺度漩涡蕴涵着海洋洋流的许多动力学信息。它对我们的海洋研究具有重要意义,如洋流,海洋渔业等。近年来出现许多漩涡提取的方法,例如,采用水文观测的方法(以设立各种浮标收集海洋资料的方法)不仅要耗费昂贵的人力物力且无法覆盖广大区域。本文提出一种借助星载传感器的温度场(SST)数据实现自动提取中尺度漩涡的技术方法。本技术借助漩涡与温度场(具有一定结构的温度场)之间存在的对应关系,通过分析温度场数据的特征获取漩涡的信息,从而实现自动提取漩涡的目标。本方法分为三个步骤:首先对温度场数据进行处理,得到温度等值线并对闭合等值线进行分组;然后就各分组闭合等值线来计算其特征参数;最后利用粗糙集理论对这些闭合等值线分组实现分类。研究中所使用的决策表,是以海洋学家从温度场影像中识别出的多个漩涡作为基础生成的,这样我们就可以利用专家的知识方便地从其他温度场影像中提取出漩涡。本文采用北大西洋湾流实例作为我们研究对象,实验表明本文采用的方法行之有效。     

High-resolution satellite measurements of coastal wind field and sea state

Methods to derive wind speed and sea state by simple empirical models from synthetic aperture radar (SAR) data are presented and applied for use in high-resolution numerical modelling for coastal applications. The new radar satellite, TerraSAR-X (TS-X), images the surface of the sea with a high resolution up to 1 m. Therefore, not only wind information and integrated sea state parameters but also individual ocean waves with wavelengths down to 30 m are detectable. Two-dimensional information on the ocean surface retrieved using TS-X data is validated for different oceanographic applications: derivation of finely resolved wind fields (XMOD algorithm) and integrated sea state parameters (XWAVE algorithm). Both algorithms are capable of taking into account fine-scale effects in coastal areas. Wind and sea state information retrieved from SAR data are applied as the input for a wave numerical spectral model (wind forcing and boundary condition) running at a fine spatial horizontal resolution of 100 m. Results are compared to collocated buoy measurements. Studies are carried out for varying wind speeds and comparisons against wave height, simulated using original TS-X-derived wind data, showing the sensitivity of waves to local wind variation and thus the importance of local wind effects on wave behaviour in coastal areas. Examples for the German Bight (North Sea) are shown. The TS-X satellite scenes render well-developed ocean wave patterns of developed swell at the sea surface. Refraction of individual long swell waves at a water depth shallower than about 70 m, caused by the influence of underwater topography in coastal areas, is imaged on the radar scenes. A technique is developed for tracking wave rays depending on changes in swell wavelength and direction. We estimate the wave energy flux along wave tracks from deep water to the coastline based on SAR information: wave height and wavelength are derived from TS-X data.     

Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions

This paper deals with meniscus deformation and flow in an isothermal liquid bridge maintained between two circular rods, when one rod is subject to axial monochromatic vibrations. It concerns a fundamental aspect of the problem of crystal growth from melt by the floating-zone technique which is often considered in weightlessness conditions. In the absence of vibrations the bridge is cylindrical; but due to vibration the mean shape of the meniscus is no more cylindrical and the meniscus oscillates around this mean shape. Two models are developed. First, we take into account the pulsating deformations of the meniscus (free surface), but we assume that the mean shape of meniscus remains cylindrical (i.e., we neglect the influence of vibration on this mean shape). For this simple case, a solution of the problem for the pulsating meniscus deformations and the pulsating velocity field is found in explicit form. For the mean flow, the problem is solved numerically by a finite-difference method. The calculations demonstrate the contribution of two basic mechanisms of mean flow generation due to vibrations, related to the generation of mean vorticity in the viscous boundary layer near the rigid boundaries and surface-wave propagation at a free surface. The intensity of the mean flow induced by surface waves is found to be sharply increasing when the vibration frequency approaches the resonance values that are determined from the explicit form of the solution of pulsation problem. In the second model, we take into account both pulsating and mean deformations of the meniscus. The governing equations for the potential of pulsating velocity and mean velocity, and for the pressure, are solved by using a finite-difference method and a boundary-fitted curvilinear coordinate system fitting the free surface.     

基于随机数的光照海浪场景模拟

海浪场景的建模是数字海洋的重要组成部分。本文用随机数模拟海浪,海浪的位置大小和波动都是随机的,海浪在涌向岸边的过程中随机生成新的海浪。海面反射光用Phong光照模型模拟,求出关键点得到太阳在海面的映像。该模型生成的实时3D大尺寸光照海浪模型在运动中不会重复,适合海面的数字化再现和海洋要素的仿真。     

Information‐driven robotic sampling in the coastal ocean

Efficient sampling of coastal ocean processes, especially mechanisms such as upwelling and internal waves and their influence on primary production, is critical for understanding our changing oceans. Coupling robotic sampling with ocean models provides an effective approach to adaptively sample such features. We present methods that capitalize on information from ocean models and in situ measurements, using Gaussian process modeling and objective functions, allowing sampling efforts to be concentrated to regions with high scientific interest. We demonstrate how to combine and correlate marine data from autonomous underwater vehicles, model forecasts, remote sensing satellite, buoy, and ship‐based measurements, as a means to cross‐validate and improve ocean model accuracy, in addition to resolving upper water‐column interactions. Our work is focused on the west coast of Mid‐Norway where significant influx of Atlantic Water produces a rich and complex physical–biological coupling, which is hard to measure and characterize due to the harsh environmental conditions. Results from both simulation and full‐scale sea trials are presented.     

Numerical simulation of molecularly thin lubricant film flow due to the air bearing slider in hard disk drives

In this paper we numerically study the evolution of depletion tracks on molecularly thin lubricant films due to a flying head slider in a hard disk drive. Here the lubricant thickness evolution model is based on continuum thin film lubrication theory with inter-molecular forces. Our numerical simulation involves air bearing pressure, air bearing shear stress, Laplace pressure, the dispersive component of surface free energy and disjoining pressure, a polynomial modeled polar component of surface free energy and disjoining pressure and shear stress caused by the surface free energy gradient. Using these models we perform the lubricant thickness evolution on the disk under a two-rail taper flat slider. The results illustrate the forming process of two depletion tracks of the thin lubricant film on the disk. We also quantify the relative contributions of the various components of the physical models. We find that the polar components of surface free energy and disjoining pressure and the shear stress due to the surface free energy gradient, as well as other physical models, play important rolls in thin lubricant film thickness change.     

我国海岸带及其近海资源环境监测的遥感技术应用

海岸带及其近海自身丰富的自然资源和优越的地理位置是国家经济发展的重要区域。如何利用多源、多通道、多时相、主被动融合的星载遥感数据获取海岸带及其近海资源环境信息是遥感应用技术的重要任务之一。本文依据国内外环境遥感应用技术的研究与发展,归纳了我们在我国海岸带及其近海资源环境遥感信息研究及其在国家有关工程计划中的应用,包括海岸带典型地物信息提取、淤泥质潮滩水边线信息提取、淤泥质潮滩冲淤变化、悬浮泥沙信息提取、内波信息提取。     

机载真实孔径雷达在中小尺度区域海洋遥感中的应用

详细介绍一个适用于中小尺度区域海洋遥感图像采集和科学研究的双极化X 波段机载真实孔径雷达。这个真实孔径雷达曾参加1996 年度、1997 年度和1999 年度美国海军实验室主持的切萨皮克湾( Chesapeake Bay) 淡水层实地考察实验。实验结果表明应用民用产品集成的廉价机载实孔径雷达可以成为研究中小型海洋现象, 如油层污染, 内波和海口淡水层及其边缘等的高性价比的有力遥感工具。文章还探讨了应用于海洋表面遥感的机载真实孔径雷达的系统设计, 最优参数和实践中的局限性。     

Theoretical study of vibrational contribution on cluster formation in a binary alloy system

Lattice vibrational effects in the process of precipitation in a binary alloy system has been studied theoretically. We derived a cancellation condition of vibrational free energy change due to cluster formation within the first order approximation, in terms of the nearest bond pair interaction. Vibrational contribution to the free energy is calculated for a specific example of cluster formation from isolated atoms, and it is almost perfectly vanished when the unlike atom potential is assumed to be the geometric mean of their constituent potentials.     

Upwind methods for hyperbolic conservation laws with source terms

This paper deals with the extension of some upwind schemes to hyperbolic systems of conservation laws with source term. More precisely we give methods to get natural upwind discretizations of the source term when the flux is approximated by using flux-difference or flux-splitting techniques. In particular, the Q-schemes of Roe and van Leer and the flux-splitting techniques of Steger-Warming and Vijayasundaram are considered. Numerical results for a scalar advection equation with nonlinear source and for the one-dimensional shallow water equations are presented. In the last case we compare the different schemes proposed in terms of a conservation property. When this property does not hold, spurious numerical waves can appear which is the case for the centred discretization of the source term.     

Gravity capillary waves generated by a moving pressure distribution in the presence of constant vorticity and dissipation

Two-dimensional nonlinear free-surface flows due to a pressure distribution moving at a constant velocity at the surface of a fluid of infinite depth are considered. The effects of the gravity and of the surface tension are included in the dynamic boundary condition. The vorticity in the fluid is assumed to be constant. The dissipation is modelled by a quasi potential approximation. The problem is solved numerically by a boundary integral equation method and numerical solutions are presented. The results unify previous findings for irrotational gravity capillary waves, waves in the presence of constant vorticity and free surface flows with dissipation.     

Global distribution of Case-1 waters: An analysis from SeaWiFS measurements

“Case-1” has been a term frequently used to characterize water type since the seventies. However, the distribution of Case-1 waters in global scale has been vague, though open ocean waters are often referred to as Case-1 in the literature. In this study, based on recent bio-optical models for Case-1 waters, an inclusive and quantitative Case-1 criterion for remote sensing applications is developed. The criterion allows Case-1 waters to have about two-fold variations of non-pigment absorption and particle backscattering around their exact Case-1 values, allowing a large range of waters to be classified as Case-1. Even so, application of this criterion to ocean color data from the SeaWiFS satellite sensor suggests that Case-1 waters occupy only about 60% of the global ocean surface. Regionally, more Case-1 waters are found in the southern hemisphere than in the northern hemisphere, and most Indian Ocean waters are found to be Case-1. The Case-1 percentage and spatial distribution change with season, and with the boundaries chosen in the criterion. Nevertheless, this study for the first time provides a quantitative and geographical perspective of Case-1 waters in global scale, and further demonstrates that many open ocean waters are not necessarily Case-1.     

Detection of wave fronts in the Indian Ocean from geostationary sunglint satellite imagery

We demonstrate the potential of monitoring coherent wave fronts on the tropical ocean surface using an advanced detection algorithm applied to visible sunglint‐affected imagery from geostationary satellites. Data from MeteoSat are processed with the advanced analysis technique to reveal transient wave activity near and to the west of the Mascarene Ridge of the western Indian Ocean. The technique is based on a wavelet‐based singularity analysis which enhances the subtle but highly coherent wave patterns in the meteorological satellite data. It is likely that the patterns represent internal ocean waves, a pathway to ocean mixing and climate. The prospect for using this detection algorithm in greatly expanded satellite global surveys of wave activity is outlined.     

Statistical characteristics of anomalously large surface waves based on computational experiments

The computational experiments on modeling surface waves, which are used for studying the statistics of the occurrence of extremely large surface waves depending on the parameters of the initial waves, are considered. The sudden occurrence of abnormally large waves in the ocean is a big hazard for marine vessels and structures. In recent years, incontrovertible evidence of this phenomenon, such as instrumentation records and photographs, has been presented. The main method of studying the phenomenon of rogue waves in this work is computational experiments based on the complete nonlinear hydrodynamic equations of an ideal liquid with a free surface. The method of conformal variables that is used for the original system of equations enables one to make effective and accurate calculations by computers and computing complexes. According to the experimental results, the statistics of the occurrence of anomalously large surface waves is studied. The use of dissipation and pumping in these computational experiments has made it possible to perform continuous calculations that are not stopped if a rogue wave occurs. The intensity of the occurrence of rogue waves depending on the values of the squares of the mean steepness and wave dispersion is estimated. It is shown that doubling the computational region almost doubles the intensity. The proposed procedure of the computational experiments allows estimating the average waiting time of a rogue wave in the assigned region.     

An electrical model with equivalent elements in a time-variant environment for an ionic-polymer-metal-composite system

Ionic polymer metal composite (IPMC) is a kind of ionic electroactive polymer (EAP) smart material that can exhibit conspicuous deflection with low external voltages (~ 5 V). It can be cut in various sizes and shapes, and used and applied in robots and artificial muscles with the capability in aquatic operation. An IPMC strip can be modeled as a cantilever beam with a loading distribution on the surface. Nevertheless, the loading distribution is non-uniform due to the imperfect surface conductivity that causes four different imaginary loading distributions employed in our structural model. The difference can be up to 5 times (3:8 mm to 19 mm). In this paper, a novel linear time-variant (LTV) model is introduced and applied to model an IPMC system. This modeling method is different from previous linear time-invariant (LTI) models because the internal environment of IPMC may be unsteady due to mobile cations with water molecules. In addition, the influence of surface conductivity is simulated and proven based on this model. Finally, by applying this novel modeling method, hysteresis that exists in IPMC and affects the relationship between the output deflection and the corresponding input voltage, such as 0:1-, 0:2-, and 0:3-rad/s sinusoidal waves, has been shown and simulated.