基于Korteweg-de Vries方程解析解的海洋内波模拟研究

主要是利用非线性发展方程丰富的解析解,基于含有散射项和微扰项的Korteweg-de Vries方程对台湾东北部东海海域内波的传播特性进行研究,并着重分析海洋内波在SAR图像上的信号特征,进而讨论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.     

内波对多波束测深影响仿真研究

为了研究内波对多波束测深的影响,通过对内波建模,分别对四个区间的声线跟踪情况进行了研究分析。在此基础上,推导了针对曲线型梯度结构的声线跟踪模型,并根据该模型进行了仿真分析。仿真简单模拟了采用常梯度声线跟踪模型对曲线型梯度结构声速剖面进行声速改正的声线跟踪过程。采用仿真数据绘制了声线跟踪前后的声线示意图,并对归算前后的波束脚印位置进行了比较分析。仿真结果说明内波会给多波束的边缘波束带来大量尖峰状的浅点,而这些浅点难以用传统的声速改正模型消除。推导的针对曲线型梯度结构的声线跟踪模型可为内波的进一步研究提供理论依据,最后对未来的研究进行了展望。     

基于二次多项式拟合的超短基线声线修正方法

超短基线定位解算中的距离观测值是指换能器与水下应答器之间的直线距离,而海水声速的不均匀分布导致声波在海水中的实际传播路径为连续弯曲的曲线,需要结合实测声速剖面进行声线修正。根据声速在分层介质中的传播特性,本文提出了一种基于二次多项式拟合的声线跟踪算法,采用线性插值方法对声速剖面数据进行合理加密并按等深度进行分层,设定每层声速梯度是不断变化的,用二次多项式拟合声速,基于运动学原理建立了完整的数学解算模型。仿真结果表明,该方法修正后的水下目标分布具有明显的收敛性,且优于等梯度声线跟踪算法和等效声速剖面法,显著提高了超短基线水声定位系统的定位精度。     

海洋声速起伏对声传播及定位精度影响分析

海洋中声速起伏导致水声信道发生变化,进而引起声线到达结构的变化,对水声传播及定位精度产生一定影响。为讨论这一效应,基于TDOA体制建立了考虑声线弯曲的水下目标无源定位模型,分析了声速起伏对水下声传播路径及传播时间的影响,进而研究了声速起伏对水下无源定位测量精度影响程度。结果表明:当水平传播距离较大时,声速剖面起伏对声传播路径及传播时间的影响更为显著;以典型四元阵为例,若基线长度为20 km,接收阵位于水下5 km处,在不考虑其它随机误差影响下,海洋声速起伏造成的声源定位误差量级在0.5 m以内。分析结果有助于更好地利用环境特征优化无源定位测量方案,可为高精度水下无源定位系统设计及精度评估提供依据。     

考虑旋转向量水平分量的大洋内波方程的一个渐近解

对于考虑旋转向量水平分量的大洋内波方程,本文求出了满足该方程的波函数的一个渐近解.该渐近波函数的振荡特性得到研究,结果表明旋转向量水平分量对高模态(高波数)内波的影响是不可忽略的.     

应用非线性薛定谔方程模拟深海内波的传播

本文选取东沙岛以东深海区域,应用描述深海内波的非线性薛定谔方程,采用啁啾的思想,研究了频散和非线性效应之间的关系,模拟了深海内波的传播.数值模拟内波演变趋势与MODIS影像拍摄到的内波演变趋势基本符合,从而验证了应用非线性薛定谔方程模拟深海弱非线性内波传播的合理性.     

机载超低频雷达探测海洋内波

机载超低频雷达探测海洋内波是海洋内波探测的新方法。海洋内波使海水电导率垂向分布发生扰动,当雷达发射的电磁波探测信号传播到内波扰动界面,电磁信号发生反射,部分反射信号再次穿透海面传播到空气中并被天线捕捉,雷达系统通过处理内波界面处的反射信号并抑制海面的反射信号实现对海洋内波的探测。根据麦克斯韦方程和海水的物理性质,推导出超低频电磁波在海水中的传播特性,研究海水温度、盐度变化对海水电导率的影响,根据KDV方程解和垂向特征函数解构造了海洋内波垂向结构,仿真了雷达接收到的海表面处、内波界面处的反射信号及其延迟时间,仿真结果表明,可以使用该方法探测海洋内波。     

基于遥感图像的南海北部内孤立波及相互作用研究

本文通过对卫星遥感图像中的内孤立波及相互作用现象进行统计分析,讨论了南海北部内孤立波及相互作用现象的时空分布特征,验证了利用卫星遥感图像反演内孤立波振幅和传播速度以及研究内波相互作用现象的可行性。统计结果表明,南海北部的内孤立波主要集中在东沙群岛以及海南岛南部,内波相互作用主要集中在东沙岛西北部以及海南岛南部。本文对此给出解释:内波传播至东沙岛附近发生绕射,绕射的内波分裂成两列后以不同的传播方向继续向西传播,相遇并发生相互作用;内波在海南岛浅滩处发生反射,与后续传来的内波发生相互作用。同时,本文利用Korteweg-de Vries (KdV)方程和Benjamin-One(BO)方程,结合观测数据,对内波振幅和传播速度进行了反演实验。反演所得的内波振幅和传播速度与南海北部实际内波振幅和传播速度相近。     

基于快速行进算法的南海内波传播模型

南海内波水平二维空间位置的估计和预测具有应用价值。一个简单而精确的估计南海非线性内孤立波地理位置的经验模型已由Jackson(2009)提出,该模型将快速行进算法应用于海洋内波传播并给出内波相速度与深度关系的经验模式函数。本文尝试用KdV方程计算非线性内波相速度,以探讨海水层化对相速度和内波传播的影响。初步结果表明,海水层化的时空差异在内波传播过程中不可忽略。本文进一步将考虑海水层化的非线性内波相速度代替文献中的经验模式函数,建立不依赖于现场实测数据的基于快速行进算法的南海内波传播模型,并给出计算个例。本文模型的计算结果从个例来看与文献一致。     

东海PN断面黑潮区域海底起伏对声传播的影响

利用2001年3月东海PN断面“973”调查获得的CTD数据，用数值模拟方法研究了PN断面黑潮区域海底起伏对声传播的影响。由深水区向浅水区传播，随着海底的抬升声线的海底反射和海面反射次数增加，声强衰减更快，限制声传播距离。由浅水区向深水区传播，随着海底降低声线上反转点深度增加，传播一定距离后部分声线不能到达上层水体，于是声强衰减也增快。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

A Review of Some Environmental Issues Affecting Marine Mining

This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be sitespecific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of "marine snow" (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested.     

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Determination of In Situ Sediment Shear Strength from Advanced Piston Corer Pullout Forces

The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Flow Cytometric Analysis of Coastal Lagoon Bacterioplankton and Picophytoplankton: Fixation and Storage Effects

The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics.