Compound compensation strategies for wireless data communicationsover the multimodal acoustic ocean waveguide

Underwater acoustic communications (UAC) at the reverberation-limited range results in severely distorted information signals. Wide-band signals are subject to both intermodal and intramodal-type of dispersions. The underwater acoustic channel impulse response and the sidelobes strongly depend on the waveguide structure and the source and receiver positions. The motion and displacement from this position, as well as other environmental variabilities impose a real-time adaptivity for the receiver operation to keep track of the fluctuations. To increase the system's reliability and data rate, there is a need to employ adaptive equalizers and diversity techniques to improve the margins against noise, and intersymbol interference (ISI). Blind adaptive equalization (BAE) is the ideal adaptive compensation when operating point-to-multipoint networks, and centralized communication systems in general. Inherent optimum multiple resonant modes within the ocean acoustic waveguide can be exploited judiciously via a new proposed parallel data multicarrier modulation (MCM) scheme by sending data over the multiple subcarriers. MCM might eventually obviate equalization which introduces higher-order computational complexity to the receiver. The above modulation eliminates multipaths and allows operation at multiples of the single-carrier transmission rate. The system's immunity to distortions such as ISI, fast fades, and impulsive noises, is increased due to incorporation of symbol guard space. Direct comparisons with single carrier schemes (such as higher-order statistics (HOS)-based equalization) are of great interest, since the proposed new receiver configuration has low-complexity to provide a compact, portable and low-power practical acoustic modem. Finally, network topology issues are considered to determine optimum network architectures for underwater acoustic LANs. A central topology (CT) supported by BAE and MCM transmission is proposed     

Reflection profiling in the deep ocean using a near bottom hydrophone

A 20 km long high resolution seismic reflection profile was carried out approximately 300 km southwest of Bermuda. The data were collected using a small airgun sound source and a single hydrophone receiver towed 100 m above the seafloor at a depth of 5400 m. Comparisons with nearby conventional seismic reflection profiles show the considerable improvement of resolving power provided by this method, particularly of the basement morphology beneath the 700 m thick sediment column. The data were recorded digitally and selected data examples show the enhancement provided by filtering, stacking, source deconvolution and corrections for hydrophone motion. The precise picture of basement topography that results from this data is compared with deep tow bathymetry profiles of the present day mid-Atlantic Ridge flanks, and is seen to be remarkably similar.     

Improvements in acoustic sediment concentration profiling using anLMS compensation algorithm

In sediment concentration profiling, sound attenuation becomes important for high-frequency acoustic backscattering systems (ABSS) when sediment concentration is high and/or the range of remote sensing is long. In the present study, a test of a least mean square (LMS) compensation algorithm was performed in order to determine the advantages over the more frequently used iteration algorithm. Numerical simulation and laboratory experiments in a mixing tank as well as an open channel suggest that the new algorithm is much more robust to white Gaussian noise and fixed-echo noise, and errors do not accumulate along the profiling path. Good linearity of this instrument in concentrations up to 20 kg/m^-3 is found by comparison with a suction-sampler. In the mixing tank, backscattering intensity profiles in concentrations up to 120 kg/m^-3 vary little along a propagation path of 40 cm and fit well to the expected homogeneous concentration. Furthermore, by using the oscillation errors in the LMS solution, a procedure has been developed to compensate for the errors in the instrument constants evaluated from the attenuation between the transducer and the first measuring volume. The feasibility of the proposed instrument-constant compensation is verified by experiments. This allows instantaneous correction of the influence of sediment deposition on the transducer surface which is important when the system is applied to coastal investigation     

An inverse ocean modeling system

The implementation of a system for variational assimilation of data into ocean models is described. The system is modular: the ocean dynamics may be changed by replacing subroutines for the tangent-linear forward model and for the adjoint model. The assimilation is `weak': the ocean dynamics need not be satisfied exactly. An iterative algorithm within the system enables the solution of nonlinear assimilation problems. There is a suite of diagnostics including posterior error statistics, term balances and array assessment. The system has been in development for over a decade, and has been used in conjunction with a variety of oceanic, atmospheric and coupled models, with real data in quantity. The algorithms used in these applications, and the particular scientific assumptions and results, have been reported elsewhere. The emphasis in this article is on the implementation. This is a considerable challenge, both in the scale and complexity of the calculations, over and above those of the underlying ocean model. The vehicle for this presentation is a `toy' model, defined by a single nonlinear equation of motion. Code for real models is available at an anonymous ftp site. Components of the code are matched here in detail to stages of the assimilation algorithm and the diagnostics. Options are given for preconditioning, parallelization, memory management and other performance issues. Resource requirements, from computing speed through preconditioning effort to algebraic derivation, are also discussed in detail. Several applications are reviewed with the emphasis, again, on implementation.     

A global ocean observing system framework for sustainable development

Sustainable development depends on maintaining ecosystem services which are concentrated in coastal marine and estuarine ecosystems. Analyses of the science needed to manage human uses of ecosystem services have concentrated on terrestrial ecosystems. Our focus is on the provision of multidisciplinary data needed to inform adaptive, ecosystem-based approaches (EBAs) for maintaining coastal ecosystem services based on comparative ecosystem analyses. Key indicators of pressures on coastal ecosystems, ecosystem states and the impacts of changes in states on services are identified for monitoring and analysis at a global coastal network of sentinel sites nested in the ocean-climate observing system. Biodiversity is targeted as the “master” indicator because of its importance to a broad spectrum of services. Ultimately, successful implementation of EBAs will depend on establishing integrated, holistic approaches to ocean governance that oversee the development of integrated, operational ocean observing systems based on the data and information requirements specified by a broad spectrum of stakeholders for sustainable development. Sustained engagement of such a spectrum of stakeholders on a global scale is not feasible. The global coastal network will need to be customized locally and regionally based on priorities established by stakeholders in their respective regions. The E.U. Marine Strategy Framework Directive and the U.S. Recommendations of the Interagency Ocean Policy Task Force are important examples of emerging regional scale approaches. The effectiveness of these policies will depend on the co-evolution of ocean policy and the observing system under the auspices of integrated ocean governance.     

An operational satellite remote sensing system for ocean fishery

Ocean environmental information is very important to supporting the fishermen in fishing and satellite remote sensing technology can provide it in large scale and in near real-time. Ocean fishery locations are always far away beyond the coverage of the satellite data received by a land-based satellite receiving station. A nice idea is to install the satellite ground station on a fishing boat. When the boat moves to a fishery location, the station can receive the satellite data to cover the fishery areas. One satellite remote sensing system was once installed in a fishing boat and served fishing in the North Pacific fishery areas when the boat stayed there. The system can provide some oceanic environmental charts such as sea surface temperature (SST) and relevant derived products which are in most popular use in fishery industry. The accuracy of SST is the most important and affects the performance of the operational system, which is found to be dissatisfactory. Many factors affect the accuracy of SST and it is difficult to increase the accuracy by SST retrieval algorithms and clouds detection technology. A new technology of temperature error control is developed to detect the abnormity of satellite-measured SST. The performance of the technology is evaluated to change the temperature bias from-3.04 to 0.05 ℃ and the root mean square (RMS) from 5.71 to 1.75 ℃. It is suitable for employing in an operational satellite-measured SST system and improves the performance of the system in fishery applications. The system has been running for 3 a and proved to be very useful in fishing. It can help to locate the candidates of the fishery areas and monitor the typhoon which is very dangerous to the safety of fishing boats.     

利用Argo剖面浮标分析上层海洋对台风“布拉万”的响应

In situ observations from Argo profiling floats combined with satellite retrieved SST and rain rate are used to investigate an upper ocean response to Typhoon Bolaven from 20 through 29 August 2012. After the passage of Typhoon Bolaven, the deepening of mixed layer depth(MLD), and the cooling of mixed layer temperature(MLT) were observed. The changes in mixed layer salinity(MLS) showed an equivalent number of increasing and decreasing because the typhoon-induced salinity changes in the mixed layer were influenced by precipitation, evaporation, turbulent mixing and upwelling of thermocline water. The deepening of the MLD and the cooling of the MLT indicated a significant rightward bias, whereas the MLS was freshened to the left side of the typhoon track and increased on the other side. Intensive temperature and salinity profiles observed by Iridium floats make it possible to view response processes in the upper ocean after the passage of a typhoon. The cooling in the near-surface and the warming in the subsurface were observed by two Iridium floats located to the left side of the cyclonic track during the development stage of the storm, beyond the radius of maximum winds relative to the typhoon center. Water salinity increases at the base of the mixed layer and the top of the thermocline were the most obvious change observed by those two floats. On the right side of the track and near the typhoon center when the typhoon was intensified, the significant cooling from sea surface to a depth of 200×104 Pa, with the exception of the water at the top of the thermocline, was observed by the other Iridium float. Owing to the enhanced upwelling near the typhoon center, the water salinity in the near-surface increased noticeably. The heat pumping from the mixed layer into the thermocline induced by downwelling and the upwelling induced by the positive wind stress curl are the main causes for the different temperature and salinity variations on the different sides of the track. It seems that more time is required for the anomalies in the subsurface to be restored to pretyphoon conditions than for the anomalies in the mixed layer.     

A versatile sonar system for ocean research and fisheries applications

An echo sounder has been developed with features ideally suited to oceanographic and fisheries research. Instruments commonly used for such research are inaccurate, limited in dynamic range, unstable, and generally inflexible. An effort has been made to overcome these deficiencies with the sonar system discussed here. The echo sounder to be described has a time-varied-gain receiver (20 log_{10} Ror40 log_{10} R + 2alphaR) accurate to withinpm0.5dB over a 100-dB range. The equivalent dynamic range is 140 dB (the ratio of the maximum signal at minimum gain to the equivalent input noise at maximum gain in a 4-kHz bandwidth). The temperature stability ispm0.5dB from10degto35degC at any range. Operating parameters, including frequency, can be easily altered to accommodate a variety of needs.     

An alternative coordinate system for solving finite difference ocean models

An alternative ‘compressed’ coordinate system for representing finite difference grids in ocean models is presented and compared with the traditional Cartesian method. The alternative method represents any arbitrary three-dimensional domain as a one-dimensional vector. Advantages of using this method include the exclusion of all land ‘dry’ points from the computational grid, leading to savings in the memory used and increased execution speed where domains have a low ratio of wet to total computational cells. The Cartesian and compressed models are applied to a variety of domains to assess the performance of each in terms of memory use and computational speed.     

海底电缆鬼波压制及陷频补偿方法研究

受到海底、自由表面等强反射界面的影响, 在海底电缆采集的地震资料中鬼波干扰往往非常发育, 在频谱中表现为明显的陷频现象, 严重影响地震剖面的质量, 给后期的处理解释带来困难。为克服这一困难, 根据海底电缆双检(陆检和水检)对下行波场的不同响应, 在深入研究伪多道匹配滤波技术的基础上提出了伪多道双检合成方法。与传统的求取反射系数的双检合成方法不同, 该方法完全数据驱动。在合成数据和渤海地震资料的实际应用中, 鬼波成分得到了明显的压制, 同时拓宽频带, 补偿陷频, 证明了该方法的有效性。     

水下机器人主动升沉补偿系统研究

介绍一种基于水下机器人常规液压收放绞车的主动升沉补偿系统,利用加速度传感器获得母船的升沉运动信号,控制绞车的运转来降低母船的升沉运动对水下机器人的影响。通过理论计算建立主动升沉补偿系统的数学模型,仿真分析绞车运动对水下机器人升沉运动的补偿效果,并利用主动升沉补偿系统实验台验证基于常规液压收放绞车的主动升沉补偿方案的可行性。     

Estimating the compensation irradiance in the ocean: The importance of accounting for non-photosynthetic uptake of inorganic carbon

The compensation irradiance, the irradiance at which net photosynthesis is zero over a 24-h period, was estimated at station ALOHA (22°45′N, 158°W) from analysis of ¹⁴C uptake rates measured from 8 January 1989 to 13 June 1990 at depths ranging from 5 to 175 m. The estimates were made on the basis of linear regressions of the difference between light bottle and dark bottle ¹⁴C uptake in the light-limited region of the euphotic zone and determination of the depth at which the difference between the uptake rates was zero. About half of the non-photosynthetic ¹⁴C uptake at the compensation irradiance could be attributed to chemolithoautotrophy; the remainder was presumably due to anaplerotic processes. Deriving the compensation irradiance by extrapolating dawn-to-dawn light-bottle uptake above the compensation irradiance to zero resulted in underestimation of the compensation irradiance by a factor of 2. We estimated the compensation irradiance at station ALOHA to be 0.054 mol-photons m⁻² d⁻¹, about 0.11% of surface 400–700 nm radiation and 1% of surface 475-nm (blue) light.     

基于 Web海洋卫星遥感产品的查询系统

对基于Web海洋卫星遥感产品查询系统的构架、数据库的建立和动态网页的编程作了介绍与分析。该查询系统采用了数据层、业务层、表示层三层体系的组织方式,利用VC++开发的程序,数据层对遥感专题产品自动创建元数据信息库进行管理,业务层和表示层均采用ASP.NET技术。该查询系统已通过了国家海洋局第二海洋研究所局域网的测试,并对遥感专题产品进行网上实时发布。该系统的安全性和稳定性还有待于进一步完善和提高。     

An improved parachute drogue system for monitoring currents in the deep ocean

A parachute drogue is described that can quickly be assembled and easily launched at sea. An anchored buoy, which provides a reference from which drogue trajectories can be determined is also described and methods for launching are outlined. This buoy, which can be moored in several kilometers depth, will extend to the deep ocean the use of drogue monitoring techniques capable of defining wind driven currents and their short-term periodicities.     

Evaluation of the ocean governance system in Korea

Considering the small land, dense population and poor natural resources, the oceans are important to Korea, but the recognition of oceans has been weak in Korean society. So ocean governance was fragmented in both institution and policies, which resulted in serious problems in the coastal waters and oceans. However, a series of maritime accidents and failures of policies increased the recognition of the coastal waters and resources and led to the establishment of one single ocean-related governmental agency in 1996. Over the last decade, the ocean governance in Korea has been successful and strong.     

Optimization of an ocean thermal energy conversion system

The optimum performance of a simple Rankine cycle ocean thermal energy conversion plant is investigated analytically. It is shown that the ratio of maximum net power output to heat exchanger surface area varies as H(Δt − t₀)² where H describes the overall heat transfer properties of the evaporator and condenser, Δt is the temperature difference between the warm and cold sea water supplies, and t₀ is a parameter depending primarily upon the pressure drops across the warm and cold sea water pumping systems. The model is relatively insensitive to the choice of working fluid, although ammonia is used as the illustrative example.     

数字海洋可视化系统研究与实现

球体模型系统是目前GIS领域的研究热点,它以强大的空间数据管理能力,丰富直观的信息表现能力迅速成为空间信息集成共享的有力平台.以Skyline软件平台为基础,介绍了数字海洋可视化系统的体系架构、功能设计和技术实现方法.实践应用表明,该系统在多源海洋信息可视化集成共享方面具有良好的应用前景.     

美国海军海洋业务预报纵览

回顾了过去几十年美国海军海洋学的发展历程,介绍了海军海洋学业务保障体系,对其科研机构和研发机制以及业务系统发展特点进行总结,同时指出美国海军海洋预报业务系统和总体科研发展规划。通过深入分析国外海洋气象科技发展的最新动态和海洋气象预报业务科研建设的最新成果,对我国海洋气象事业的业务发展和科研规划提供有价值的参考。     

多参数海洋浮标实时采集系统的设计

提出了一种深海浮标实时数据采集的设计方案。该方案基于数据库和卫星通信技术,通过多通道数据采集,能够实现深海环境要素的实时获取,完成在无人值守状态下浮标周围海域的环境监测,有助于推动特定海域海洋环境的研究。     

海上浮体动力定位外力计算

动力定位系统（dynamic positioning system）是一种闭环自动控制系统,采用推力器来抵抗风、浪、流等作用在浮体上的境力,使其保持在所要求的位置上。船舶的风和流作用力由经验公式求得,波浪力主要考虑二阶漂移力,由三维势流理论的直接积分法求得。通过模拟仿真,表明其结果能够用于船舶动力定位系统研究。