一种改进的扇形波束旋转扫描散射计海面风矢量反演算法

扇形波束旋转扫描散射计（RFSCAT）是约十年前才被提出来的一种新型星载微波散射计。与其它旋转扫描散射计类似,其星下点附近区域和刈幅边缘区域的风场反演误差相对较大。在本文设定的参数条件下,RFSCAT散射计刈幅边缘区域的风向反演精度相对于轨道中间区域降低了约9°。针对这一问题,本文为RFSCAT散射计提出了一种改进的风矢量反演算法。新算法的主要特征是,根据风向反演偏差直方图,在整个刈幅区域内,对模糊解风向取值区间进行自适应扩展,以获取并保留更多可能风向解。利用模拟的100条轨道的L2A数据,对新算法进行反演验证。实验结果证明,新算法能够有效改善RFSCAT散射计星下点附近区域和轨道刈幅边缘区域的风向反演精度。星下点和刈幅边缘上的风矢量单元的风向反演精度相对于标准的MLE算法分别提高了1.6°和9°。     

星载全极化微波散射计仿真与海面风场反演研究

通过建立全极化微波散射计系统仿真模型,探索全极化微波散射计的风场反演方法;通过对比不同仪器测量精度下全极化和同极化微波散射计风场反演结果,分析评价全极化微波散射计系统反演海面风场的性能.全极化微波散射计通过增加测量信息来减少模糊解出现的概率,进一步提升风场反演精度.结果表明全极化微波散射计相比同极化微波散射计具有更好的风场反演性能,对于风向结果的改善较为明显:在仿真实验中,全极化仿真反演的风速误差结果优于同极化10°以上,证明了全极化微波散射计能够提升风场反演性能.该仿真结果对我国后续海洋卫星的研发具有一定的借鉴作用.     

基于遗传算法的微波散射计海面风矢量反演研究

针对目前传统反演方法存在的不足和限制,引入遗传算法用于风矢量反演中的目标函数优化.以SeaWinds散射计为例,根据其模型函数和模糊解的基本特征,设计并实现了一套可用于该散射计的海面风矢量反演算法,并利用SeaWinds散射计部分L2A实测数据对该反演算法进行了验证.实验结果表明,通过多代遗传操作,算法能够收敛于几个局部极值点,从而证明该算法能够有效解决数值风矢量的优化搜索问题.     

海洋二号卫星散射计风场产品真实性检验及分析

利用国际海-气综合数据集(ICOADS)中的海面风场实测数据作为真实值,对海洋二号卫星散射计风场产品进行真实性检验,得到初步结论:(1)在中、低风速条件下,海洋二号散射计风速与ICOADS实测风速具有较好一致性,但在较高风速条件下海洋二号散射计会出现风速低估现象;(2)海洋二号散射计风向与ICOADS实测风向的误差主要集中在-15°—15°范围内,在低风速条件下,海洋二号散射计与ICOADS两者风向存在较大偏差,风向多解也主要发生在低风速时;(3)在2—24 m/s风速条件下,剔除超过3个标准偏差风速样本后,海洋二号与ICOADS两者风速的平均绝对误差为1.36 m/s,均方根误差为1.92 m/s,若忽略风向多解的影响,两者风向的平均绝对误差为14.98°,均方根误差为20.21°。     

星载散射计资料反演带有气旋及锋面的复杂风场

气象预报在确定热带气旋中的大风（风速17．2～20．7m／s）半径时，由于热带海洋地区在恶劣气候下缺乏现场数据，往往过高地估计了大风半径。星载散射计在探测海面上的风矢量的同时，也探测到许多热带气旋。本文利用Seasat－A卫星上的散射计（SASS）资料反演计算海面风暴的风矢量，并利用风速等值线进行风向多解排除，计算结果表明：星载散射计能探测到大风的阈值（17～18m／s），其准确度为2m／s或±10％（取大者）。     

基于微波多载荷优势互补的海面风场联合反演方法研究

海面风场的遥感探测主要通过合成孔径雷达（Synthetic Aperture Radar,SAR）和微波散射计等微波遥感器进行,近年来波谱仪也可用来探测风场信息。各遥感器独立工作,具有不同的入射角、覆盖范围和分辨率,在风场探测方面各有其优势和局限性。本文基于各类微波遥感器独特的观测方式,根据各自的时空匹配规则,相互借助实现3种载荷的两两联合,波谱仪和散射计分别与SAR联合为其提供风向并得到SAR的风速结果,与ERA5的均方根误差分别为1.972 7 m/s和1.986 0 m/s,散射计与波谱仪相互联合为波谱仪去除风向模糊,去模糊的风向结果为26.758 9°,都符合目前风场反演公认的标准,风速和风向的均方根误差小于2 m/s和30°。本文解决了现阶段单模式观测风场的缺陷,为我国未来发射SAR、散射计、波谱仪多载荷卫星的风场反演提供互补信息的支持,为实现多载荷区域大范围高精度风场研究做准备。     

一种修正的SeaWinds散射计圆中数滤波法

利用最大似然法(MLE)对SeaWinds散射计数据反演得出的风矢量一般存在2—4个模糊解,而且第1模糊解构成的风场在轨道外侧区域容易出现块状模糊,所以不能像SASS和NSCAT等散射计那样,以第1模糊解初始化风场后用圆中数滤波法进行模糊去除。文章根据SeaWinds散射计第1模糊解的空间分布特性,对传统圆中数滤波法进行了修正,使之适合SeaWinds散射计的模糊去除,即在缺乏参考数据进行初始化的前提下,能够有效去除块状模糊问题。     

中法海洋卫星微波散射计风场反演残差特性研究

2018年10月发射的中法海洋卫星散射计(CSCAT)是国际上首个扇形波束旋转扫描微波散射计。本文以最大似然估计风场反演算法为基线,详细分析了中法海洋卫星微波散射计海面风场反演代价函数的残差特性,重点研究了新的观测几何对风场反演残差以及风场质量的影响,并建立了风场模糊解的似然概率模型函数。结果表明,CSCAT风场反演的残差特性随风矢量单元在刈幅交轨方向位置的变化而变化,模糊解似然概率模型函数的指数分布在?0.4～?1.8之间。分析结果为CSCAT风场质量控制和二维变分分析去模糊算法的精细化调整提供了重要的参考。     

星载微波散射计两种体制的比较

星载微波散射计可以提供全球、全天候、高精度、高分辨率和短周期的海面风场数据。根据雷达天线足印的形状,雷达散射计主要包括扇形波束体制与笔形波束体制两种形式。概述了两种体制微波散射计在设计结构及后期数据处理算法中的优缺点,并对两种不同体制散射计的系统仿真数据进行比较。分析结果表明:对于小型卫星平台,Ku波段的旋转扫描扇形波束散射计比笔形波束圆锥扫描散射计具有更优的风场反演性能。     

神经网络反演散射计风场算法的研究

建立了一个神经网络反演卫星散射计海面风场的B-P算法,给出了一个神经网络反演风场的模型,并利用该反演算法和模型对实际卫星散射计数据进行了海面风场反演试验,对风向的多解性利用圆中数滤波方法进行排除.对神经网络训练和检验数据集分别采用ERS-1/2散射计数据和欧洲中期天气预报(ECMWF)提供的风场作为配准点数据.把反演的风速和风向与CMCD4和ECMWF的风场作了比较,它们吻合得比较好;研究表明神经网络反演海面风场是可行和高效的.     

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.     

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。     

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.     

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.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

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.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.