渤海近岸水体后向散射系数反演模型

水体后向散射系数bb是重要的海洋光学参数,在以悬浮物为主要组分的浑浊二类水体中,其对于水体光学性质起着决定性的作用,该参数的遥感反演对于海洋光学与水色遥感研究具有重要意义.利用2005年渤海近岸水体实测数据集,建立了基于水体遥感反射率光谱数据的后向散射系数bb(λ)经验反演模型(λ=442 nm,488 nm,532 nm,589 nm,676 nm),经实测数据检验,bb(442)和bb(589)反演平均相对误差约为30%;bb(488)和bb(676)反演半均相对误差优于40%;bb(532)反演半均相埘误差约为57%.通过分析模型对于输入误差的敏感性发现,当输入端引入±5%的误差时,模型反演值的误差波动在绝大多数情形下可控制在±10%以内,模型足稳定可靠的.模型适用于渤海近岸浑浊水体,可用丁水体光学参数的时空分布特征分析以及基丁固有光学参数的水色组分遥感反演.     

Acoustic radiation force on a sphere in standing and quasi-standing zero-order Bessel beam tweezers

Starting from the exact acoustic scattering from a sphere immersed in an ideal fluid and centered along the propagation axis of a standing or quasi-standing zero-order Bessel beam, explicit partial-wave representations for the radiation force are derived. A standing or a quasi-standing acoustic field is the result of propagating two equal or unequal amplitude zero-order Bessel beams, respectively, along the same axis but in opposite sense. The Bessel beam is characterized by the half-cone angle β of its plane wave components, such that β = 0 represents a plane wave. It is assumed here that the half-cone angle β for each of the counter-propagating acoustic Bessel beams is equal. Fluid, elastic and viscoelastic spheres immersed in water are treated as examples. Results indicate the capability of manipulating spherical targets based on their mechanical and acoustical properties. This condition provides an impetus for further designing acoustic tweezers operating with standing or quasi-standing Bessel acoustic waves. Potential applications include particle manipulation in micro-fluidic lab-on-chips as well as in reduced gravity environments.     

基于灰色关联度的中国海洋产业结构分析

简要分析了中国海洋经济的发展现状与趋势, 着重对我国主要海洋产业进行了关联度分析, 得出我国海洋经济的支柱产业和主导产业以及海洋产业结构存在的问题, 并据此提出了中国海洋产业结构优化升级对策等方面的建议.     

A High-Efficiency Spectral Method for Two-Dimensional Ocean Acoustic Propagation Calculations

The accuracy and efficiency of sound field calculations highly concern issues of hydroacoustics. Recently, one-dimensional spectral methods have shown high-precision characteristics when solving the sound field but can solve only simplified models of underwater acoustic propagation, thus their application range is small. Therefore, it is necessary to directly calculate the two-dimensional Helmholtz equation of ocean acoustic propagation. Here, we use the Chebyshev–Galerkin and Chebyshev collocation methods to solve the two-dimensional Helmholtz model equation. Then, the Chebyshev collocation method is used to model ocean acoustic propagation because, unlike the Galerkin method, the collocation method does not need stringent boundary conditions. Compared with the mature Kraken program, the Chebyshev collocation method exhibits a higher numerical accuracy. However, the shortcoming of the collocation method is that the computational efficiency cannot satisfy the requirements of real-time applications due to the large number of calculations. Then, we implemented the parallel code of the collocation method, which could effectively improve calculation effectiveness.     

Observations of coastal upwelling off northwest Africa using meteosat data

Summary One month of Meteosat IR data has been used to study the upwelling phenomenon along the northwest coasts of Africa. The analysis has shown the presence of a cold water strip along the coastline (1500 km long and (100÷200) km wide) characterized by a sea surface temperature of almost 3°C lower than the surroundings. The synoptic view offered by Meteosat evidentiated the simultaneous presence of two zones of the upwelling regime characterized by a different behaviour: the C. Bojador zone where the oscillations of the cross-shore thermal gradient measured by satellite follow quite well the daily variation of the large-scale meteorological forcings and the C. Ghir zone where the phenomenon is not always present and is more related to local forcings and coastal geometry. The general features resulting from our study are in agreement with the results of in situ previous measurements.

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Riassunto Il fenomeno dell'upwelling lungo le coste del nord-ovest dell'Africa è stato studiato utilizzando un mese di dati del statellite Meteosat relativi al canale dell'infrarosso. L'analisi di questi dati ha mostrato la persistenza di una striscia di acqua fredda lungo costa (lunga circa 1500 km e larga (100÷200) km) caratterizzata da una temperatura superficiale di almeno 3 °C piú bassa rispetto alle acque circostanti. La visione sinottica di tutta la zona del nord-ovest dell'Africa fornita dal Meteosat ha permesso di evidenziare due zone di upwelling caratterizzate da un regime differente: la zona di Capo Bojador, dove le variazioni del gradiente termico perpendicolare alla costa misurato da satellite seguono le oscillazioni dei forzanti meteorologici a grande scala, e la zona intorno a Capo Ghir, dove il fenomeno dell'upwelling non è sempre presente e dove i forzanti locali e la geometria della costa sembrano avere un ruolo predominante. Le strutture oceanografiche evidenziate dall'analisi delle immagini da satellite e la loro evoluzione temporale sono risultate consistenti con le precedenti osservazioni basate su tecniche convenzionali.

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Резюме Инфракрасные данные с метеоспутника в течение одного месяса используются для исследования явления ?апвелинга? вдоль северного побережья Африки. Проведенный анализ показывает наличие узкой полосы холодной воды вдоль береговой линии (1500 км в длину и (100÷250) км в ширину), которая характеризуется поверхностной температурой ночти на 3 °C ниже, чем температура окружающих слоёв. Данные с метеоспутника указывают на одновременное присутствие двух различных зон, которые имеют различное поведение в режиме ?апвелинга?. Общие особенности, полученные из проведённых исследований, хорошо согласуются с результатами предыдущих измерений на месте.

     

Application of finite difference method adopted in fluid mechanics to sound propagation in ducts

Researches on sound propagation problems in ducts done by the author and other investigators in recent years are briefly discussed in this paper. The finite difference method used in fluid mechanics is used for solving these problems thus presenting an aspect of the development of research work in this field at home and abroad.The project supported by National Natural Science Foundation of China.     

Linear absorbing boundary conditions for surface water wave propagation

Summary The meaning of linear absorbing boundary conditions for periodic water waves in elliptical approaches is discussed. It is found that the direction of propagation of the waves must be known for reliable boundary conditions and that the energy dissipation of waves running parallel to a boundary in general cannot be modelled in the framework of a linear theory. Work presented at the Euromech Colloquium 240 on ?Dispersive waves in dissipative fluids?, Bologna, August 30–September 2, 1988.     

Thermal expansion of a rig

Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as far as the calibration of a satellite altimeter is concerned.     

On an initial‐boundary value problem for a wide‐angle parabolic equation in a waveguide with a variable bottom

We consider the third‐order Claerbout‐type wide‐angle parabolic equation (PE) of underwater acoustics in a cylindrically symmetric medium consisting of water over a soft bottom B of range‐dependent topography. There is strong indication that the initial‐boundary value problem for this equation with just a homogeneous Dirichlet boundary condition posed on B may not be well‐posed, for example when B is downsloping. We impose, in addition to the above, another homogeneous, second‐order boundary condition, derived by assuming that the standard (narrow‐angle) PE holds on B, and establish a priori H² estimates for the solution of the resulting initial‐boundary value problem for any bottom topography. After a change of the depth variable that makes B horizontal, we discretize the transformed problem by a second‐order accurate finite difference scheme and show, in the case of upsloping and downsloping wedge‐type domains, that the new model gives stable and accurate results. We also present an alternative set of boundary conditions that make the problem exactly energy conserving; one of these conditions may be viewed as a generalization of the Abrahamsson–Kreiss boundary condition in the wide‐angle case. Copyright © 2008 John Wiley & Sons, Ltd.     

Conservation principles of the geophysical fluid dynamics for bounded basins

Summary The paper shows how a variety of quasi-geostrophic equations can be developed to obtain, in the oceanographic case, conservation principles consistently referred to bounded basins. Some unsatisfactory examples found in the literature are critically revisited.

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Riassunto Si mostra come una varietà di equazioni quasi-geostrofiche può essere elaborata in modo da ottenere, nel caso oceanografico, principi di conservazione coerentemente riferibili a bacini chiusi. Alcuni esempi tratti dalla letteratura che non soddisfano la precedente richiesta sono riesaminati criticamente.