利用卫星观测海面信息反演三维温度场

基于历史观测的温盐剖面资料,采用回归分析方法统计出海面温度异常、海面动力高度异常与温度剖面异常之间的相关关系;然后利用高分辨率的卫星遥感海表面温度(SST)和卫星观测海面高度(SSH)信息重构了三维海洋温度场。在台湾岛周边海域建立了时间分辨率为天、空间分辨率为0.25°×0.25°的三维温度分析场。通过与实测资料的比较分析,文章所构建的分析场能够较好地描述海洋三维温度场的结构特征,能够较为真实地反映海洋的中尺度变化过程。该分析场可以作为海洋数值模式的初始场,也可以作为伪观测同化到海洋数值再分析和预报系统中,进而改善三维温、盐、流的数值再分析和预报。     

基于遥感数据的温度剖面预报研究

为了提高温度剖面的预报精度,提出了一种基于遥感数据的温度剖面预报方法.文中使用27个实测温度剖面和遥感SST、SSHA数据实现了对温度剖面的预报,并用该点的ARGO数据进行了检验.实验结果表明,将遥感数据同化到温度剖面的预报中是可行的,并能有效的提高温度剖面的预报精度.     

Extrapolation of upwelling irradiance just beneath the ocean surface from the in-water radiometric profile measurements

Accurate measurements of upwelling irradiance just beneath the ocean surface,E_u(λ,0^-),can be used to calculate ocean optical parameters,and further develop retrieval algorithms for remotely sensing water component concentrations.Due to the effects of sea surface waves,perturbation from instrument platform (ship),and instrument self-shading,E_u(λ,0^-) is often difficult to be accurately measured.This study presents a procedure for extrapolating the E_...     

水温对XCTD剖面仪单模光纤传输信道影响的研究

提出采用单模光纤作为XCTD的传输信道,首先对使用漆包线作为传输信道所面临的难题进行了简要的分析;其次,分析了单模光纤技术优势;最后,针对XCTD工作环境中海水温度变化对光纤传输信道带来的影响进行了理论研究和实验验证,实验结果表明,单模光纤信道在海水介质及0~20℃海温变化下,以10 MB/S的传输速率传输数据时误码率为0,且损耗变化几乎可以忽略,大大提高了信号传输的速率和传输稳定性,实验结果说明采用单模光纤作为XCTD的传输信道具有一定的可行性。     

Microseisms and ocean wave measurements

Measurements of microseisms in Auckland, New Zealand, are compared with ocean wave data taken on the west coast of New Zealand, about 150 km southwest of Auckland. There is strong correlation at most times. Exceptions are when the Auckland area is subject to strong winds from the easterly quarter. Microseism activity in Auckland in the 0.05-1-Hz band appears to be entirely due to ocean waves     

Geodetic measurements in the ocean

This paper covers the topic of marine geodesy, its goals, and applications. Specifically discussed are position determination and establishment of geodetic control on the ocean bottom, ocean surface, and subsurface, and the determination of the geoid, a vertical reference surface. The various techniques used in position determination (including satellite, airborne, radio, inertial and acoustic techniques) are assessed in terms of accuracy, coverage, and contribution to the solution of specific problems associated with position and control. The results of several marine geodetic control experiments are presented. Classical techniques for the determination of the geoid are discussed and assessed, as are new techniques such as satellite altimetry. The outlook for marine geodetic measurements in the ocean is outlined in terms of what is being planned or considered for the next decade, and several recommendations are made.     

Assimilating temperature and salinity profile observations using an anisotropic recursive filter in a coastal ocean model

In order to improve the ocean forecasting in the North Sea and Baltic Sea, an assimilation scheme based on a bottom-topography-dependent anisotropic recursive filter has been used in this study. This scheme can stretch or flatten the shape of a local representative contour surface of the background error covariance function into the form of an ellipse. Furthermore, the computing efficiency has been largely improved due to implicit computation of the background error covariance. A two-month experiment has been used for verifying the impact of assimilating ocean profile observations on ocean forecasting. The results indicate that the use of temperature and salinity profiles can largely improve the oceanic forecasting. The root mean square differences between the forecasts and observations for temperature and salinity have been reduced by 36% and 18% in the experiment period, respectively. Moreover, it is found that the anisotropic recursive filter approach is especially efficient in areas with complex coastlines and sharp fronts, e.g., inner Danish waters. The results also show that the propagation of observation information from an observation position to its neighboring grid points is closely related to currents.     

High-frequency radar measurements of the ocean wave-directionalspectrum

Measurements of the ocean wave directional spectrum using a dual, high-frequency (HF) radar system are presented. A model-fitting technique is used to obtain wave measurements from the radar Doppler spectra. Over 100 h of data, collected NURWEC2 (Netherlands-UK Radar Wavebuoy Experimental Comparison), have been compared with measurements using a WAVEC directional wave buoy. The amplitude and directional characteristics of long-wave components at frequencies of 0.07-0.1 Hz in general show good agreement. Reasonable estimates of the directional spectrum across the whole frequency range are obtained when the assumptions of the model-fitting technique are appropriate. Remaining problems in radar measurement and difficulties in assessing accuracy are discussed     

Long-period acoustic and seismic measurements and ocean floorcurrents

Pressure fluctuations caused by a strong ocean floor current are evident during most of an eighty-day-long record of very-low-frequency acoustic ambient noise measured by an instrument on the seafloor in the western Atlantic in the framework of the HEBBLE (High Energy Benthic Boundary Layer Experiment). The differential pressure gauges on the instrument produce useful measurements over a wide frequency band extending from 0.0005 to 16 Hz. The spectrum of current-induced pressure fluctuations is red with a power-law dependence on frequency with an exponent of -1.5. Turbulence in the ocean floor boundary layer is the source of these pressure fluctuations rather than the effects of flow around the transducers. This record of boundary-layer pressure fluctuations is used to predict the effect of seafloor currents on long-period seismograph measurements from the seafloor and from under the seafloor in boreholes     

Deep ocean fluxes and their link to surface ocean processes and the biological pump

Intense studies of upper and deep ocean processes were carried out in the Northwestern Indian Ocean (Arabian Sea) within the framework of JGOFS and related projects in order to improve our understanding of the marine carbon cycle and the ocean’s role as a reservoir for atmospheric CO₂. The results show a pronounced monsoon-driven seasonality with enhanced organic carbon fluxes into the deep-sea during the SW Monsoon and during the early and late NE Monsoon north of 10°N. The productivity is mainly regulated by inputs of nutrients from subsurface waters into the euphotic zone via upwelling and mixed layer-deepening. Deep mixing introduces light limitation by carrying photoautotrophic organisms below the euphotic zone during the peak of the NE Monsoon. Nevertheless, deep mixing and strong upwelling during the SW Monsoon provide an ecological advantage for diatoms over other photoautotrophic organisms by increasing the silica concentrations in the euphotic zone. When silica concentrations fall below 2 μmol l⁻¹, diatoms lose their dominance in the plankton community. During diatom-dominated blooms, the biological pathway of uptake of CO₂ (the biological pump) appears to be more efficient than during blooms of other organisms, as indicated by organic carbon to carbonate carbon (rain) ratios. Due to the seasonal alternation of diatom and non-diatom dominated exports, spatial variations of the annual mean rain ratios are hardly discernible along the main JGOFS transect.Data-based estimates of the annual mean impact of the biological pump on the fCO₂ in the surface water suggest that the biological pump reduces the increase of fCO₂ in the surface water caused by intrusion of CO₂-enriched subsurface water by 50–70%. The remaining 30 to 50% are attributed to CO₂ emissions into the atmosphere. Rain ratios up to 60% higher in river-influenced areas off Pakistan and in the Bay of Bengal than in the open Arabian Sea imply that riverine silica inputs can further enhance the impact of the biological pump on the fCO₂ in the surface water by supporting diatom blooms. Consequently, it is assumed that reduced river discharges caused by the damming of major rivers increase CO₂ emission by lowering silica inputs to the Arabian Sea; this mechanism probably operates in other regions of the world ocean also.     

海洋表层温度剖面数值模拟

遥感测量海水表面温度(SST)需用海表面以下实测温度资料加以校正,由于长时间大范围进行海洋表层海水垂向温度剖面野外观测非常困难,建立经有限资料验证的数值模型十分重要。文章基于美国加利福尼亚湾3组船载光学实验的气象及海温资料,考虑太阳热辐射作用与海表面冷温层效应,建立了一个海表下20m深度范围内水温剖面演变的数值模型。通过冷温层计算合理加密了表层网格,使数值模型更准确地估计海表散热作用。计算结果与野外实测海温资料对比显示,海表剖面测试仪(SkinDeEP)未能准确定位和捕捉海表冷温层,实验方法有待改进。整合模型能准确描述海温剖面的演变趋势,在近海表20cm深度内,特别是与遥感SST相关的近海表1cm深度内,模拟结果优于无本皮肤层模型的计算结果。     

Deep ocean wave energy conversion using a cycloidal turbine

A lift based wave energy converter, namely, a cycloidal turbine, is investigated. This type of wave energy converter consists of a shaft with one or more hydrofoils attached eccentrically at a radius. The main shaft is aligned parallel to the wave crests and submerged at a fixed depth. In the two-dimensional limit, i.e. for large spans of the hydrofoil (or an array of these), the geometry of the converter is suitable for wave termination of straight crested Airy waves. Results from two-dimensional potential flow simulations, with thin hydrofoils modeled as either a point vortex or discrete vortex panel, are presented. The operation of the cycloidal turbine both as a wave generator as well as a wave-to-shaft energy converter interacting with a linear Airy wave is demonstrated. The impact on the performance of the converter for design parameters such as device size, submergence depth, and number of hydrofoils is shown. For optimal parameter choices, simulation results demonstrate inviscid energy conversion efficiencies of more than 99% of the incoming wave energy to shaft energy. This is achieved using feedback control to synchronize the rotational rate, blade pitch angle, and phase of the cycloidal wave energy converter to the incoming wave. While complete termination of the incoming wave is shown, the remainder of the energy is lost to harmonic waves traveling in the up-wave and down-wave directions.     

Evaluating the contribution of satellite measurements to the re-construction of three-dimensional ocean temperature fields in combination with Argo profiles

Assimilation systems absorb both satellite measurements and Argo observations. This assimilation is essential to diagnose and evaluate the contribution from each type of data to the reconstructed analysis, allowing for better configuration of assimilation parameters. To achieve this, two comparative reconstruction schemes were designed under the optimal interpolation framework. Using a static scheme, an in situ-only field of ocean temperature was derived by correcting climatology with only Argo ...     

Simulating ocean acoustic tomography measurements with Hamiltonian ray tracing

Tomographers map mesoscale ocean structure by inverting acoustic travel-time measurements through networks of underwater paths. To know where to deploy sensors and how to interpret their measurements, one must first understand the "forward problem," that is, how the sound channel and mesoscale features refract sound in three dimensions, and how such refraction alters the pulse-arrival sequence. We use a Hamiltonian ray-tracing program called HARPO to compute the refraction by continuous three-dimensional ocean models and to display the results in ways that add insight about refractive effects. We first simulate propagation in a simple range-independent sound channel, showing how pulse-arrival sequence depends on channel parameters and sensor placement. Next, we add linear range dependence and show that it is hard to extract range information from pulse measurements at one range. Finally, we add a simple model of a mesoscale eddy including its currents and show that deflection and splitting of the sound channel significantly alter the pulse-arrival sequence. Two diagrams that have not been widely used before are useful ways to display the arrival-time and ray-focusing perturbations caused by changes in ocean structure: they are plots of range versus launch angle and range versus travel time. Examples of azimuthal deflection, three-dimensional eigenrays, and reciprocal propagation through eddy currents are shown, and simplified methods for estimating the travel time of three-dimensional eigenrays are evaluated.     

包含温度因子的海水地球物理模型函数建模研究

以SeaWinds散射计为例,利用其L2A卫星测量数据和相应的海面浮标测量数据,以温度作为独立变量,借助人工神经网络首次尝试建立了包含温度因子的海水地球物理模型函数。建模实验结果表明,在3—15m.s-1风速范围内,对于两种极化方式,后向散射系数先随温度的升高而增大,当风速大于某一数值后,又随温度的升高而减小,但两种极化方式的转折风速存在差异。该研究结果为海面微波散射机理认识的进一步深入和模型函数精度的进一步提高展示了潜在的可能途径。     

Infrasonic seismic and acoustic measurements in the deep ocean

The authors compare the signal-to-noise ratios obtained on bottomed seismometers, bottomed hydrophones, and buried seismometers from near-surface explosions in the Ngendei Expedition. The data were recorded in 5.5-km-deep water in the south central Pacific Ocean with a triaxial borehole seismograph and four triaxial ocean-bottom seismographs having externally mounted hydrophones. At ranges less than 35 km, the data indicate that the ocean bottom seismometer is a superior signal detector than the ocean-bottom hydrophone, and that the subbottom seismometer is superior in performance to the ocean-bottom seismometer. Above 4 Hz, the seismometer appears to have a 10-dB signal-to-noise advantage over the hydrophone for surface explosions at ranges less than 30 km     

Efficient sensor placement for ocean measurements using low-dimensional concepts

Using simulation results from three different regional ocean models (HOPS, ROMS and FVCOM) we show that only a few spatio-temporal POD (proper orthogonal decomposition) modes are sufficient to describe the most energetic ocean dynamics. In particular, we demonstrate that the simulated ocean dynamics in New Jersey coast, Massachusetts Bay and Gulf of Maine is energetically equivalent to the wake dynamics behind a cylinder at low Reynolds number. Moreover, the extrema of the POD spatial modes are very good locations for sensor placement and accurate field reconstruction. We employ a modified POD theory to incorporate a limited number of measurements in reconstructing the velocity and temperature fields, and we study systematically the corresponding reconstruction errors as a function of the sensor location, number of sensors, and number of POD modes. This new approach is quite accurate in short-term simulation, and hence it has the potential of accelerating the use of real-time adaptive sampling in data assimilation for ocean forecasting.     

The evolution of deep ocean pressure measurements in the UK

This paper is a brief review of the work carried out by the Proudman Oceanographic Laboratory (POL) in measuring tides and sub-surface pressure variations in the deep water of the ocean basins using Bottom Pressure Recorders (BPRs). It deals particularly with the work of David Cartwright which he began in the early 1970s and carried out until he left POL in 1986 but is continued by his co-workers of that time.The paper mentions the early work in the north Atlantic when instrument deployments were limited to one month duration and describes what was achieved from the measurements. It concentrates mainly on measurements that were made since the early 1980s when it became possible, because of developments in instrument technology, to achieve individual measurements lasting for one year or more. The results obtained from these measurements are described and some interesting features of the spectrum of the pelagic sub-surface pressure are discussed.As instrument technology further improved, it became possible to study low frequency variations in sub-surface pressure. The contributions made by POL to studies of the Atlantic and Indian Oceans and the contribution to ocean circulation studies during the World Ocean Circulation Experiment are discussed. This led to the development of an instrument capable of operating continuously at ocean depths for five years. The preliminary results from a four year deployment of this instrument which was completed in November 1996 are included.     

岸基C波段和X波段雷达观测海面后向散射系数

本文给出了1992年4月中旬在浙江宁波北仑港进行的岸基X波段及C波段观测海面雷达后向散射系数σ°现场实验的部分结果，并对σ°、入射角θ、风速U及相对方位角X的关系作了讨论。实验表明，当风速在2．2～11．5m／s时，对于HH、VV及HV极化：（1）当20°≤θ＜65°时，对于X波段和C波段，σ°和exp（θ／θ。）成正比，且θ。在5°～8°之间；（2）对于X波段，当θ≤65°时。σ°比于Ur，在45°入射角VV极化时，r＝1．49；（3）σ°在逆风时接近最大，在侧风时接近最小。     

Aircraft measurements of the microwave scattering signature of the ocean

Microwave scattering signatures of the ocean have been measured over a range of surface wind speeds from 3 m/s to 23.6 m/s using the AAFE RADSCAT scatterometer in an aircraft. Normalized scattering coefficients are presented for vertical and horizontal polarizations as a function of incidence angle (nadir to55deg) and radar azimuth angle (0degto360deg) relative to surface wind direction. For a given radar polarization, incidence angle, and azimuth angle relative to the wind direction, these scattering data exhibit a power law dependence on surface wind speed. The relation of the scattering coefficient to azimuth angle obtained during aircraft circles (antenna conical scans) is anisotropic and suggests that microwave scatterometers can be used to infer both wind speed and direction. These results have been used for the design of the Seasat-A Satellite Scatterometer (SASS) to be flown in 1978 on this first NASA oceanographic satellite.