浅论海面地形特征的形成机制

本文从地热学、海洋学、气象学、物理海洋学和海底构造学角度,探讨了海面地形特征的形成机制。研究表明,形成海面地形起伏差异的主要因素有以下三个:一是有特殊的热量来源,二是有保持热量不流失的外部条件——特有的地貌特征和海底地形,三是有特殊的海流影响。     

利用卫星测高资料推求西北太平洋海域的海洋大地水准面

本文根据卫星测高数据和海面动力地形资料,绘制了西北太平洋海域局部大地水准面的精细结构图,对解决卫星测高技术中大地水准面和海面地形的可分性问题作了初步尝试。     

利用海面温度和海面动力高度反演西太平洋月平均温度场

海水三维温度场是海洋研究和海洋工程领域中最重要的数据资料之一。本研究基于量纲分析法获得海面参数和海水内部温度剖面之间的函数关系,进而提出了一种利用海面温度和海面动力高度反演大洋月平均三维温度场的方法。本研究基于该方法估算了西太平洋海域0～1 000 m深度范围月平均三维温度场,并将反演结果与基于Argo资料获得的三维温度场进行了比较,其结果证明了该方法的有效性。     

基于卫星测高的中国近海及邻域海面地形研究

为得到中国近海及邻域精度较高的海面地形,同时尽可能减少滤波对海面地形精度的影响,提出了联合卫星测高潮汐分析与XGM2019e地球重力场模型确定海面地形的方法,首先通过T/P系列(包括Jason-1、Jason-2、Jason-3)卫星测高数据潮汐分析得到沿迹点平均海面高,从中扣除根据XGM2019e重力场模型计算相应沿迹点上的大地水准面高得到沿迹点海面地形,最后通过Kriging插值和Gauss滤波得到研究区域内30′×30′海面地形模型。与DTU22同区域海面地形对比整体差异为±4.49 cm,与沿岸长期验潮站实测海面地形对比整体精度为±4.56 cm,高精度的海面地形为研究海流的变化提供了现实依据。     

测高重力场反演海底地形方法比较

根据重力异常与海底地形的相关性,利用日本西之岛附近海域内的重力异常和船测水深,分别采用SandwellSmith方法(SS,1994)和重力地质法(GGM)反演了该海域内1'×1'海底地形模型,并将反演的模型与格网化船测水深模型和ETOPO1模型进行了对比分析。在GGM中,使用了迭代法向下延拓确定密度差常数为5.7g/cm~3。与SS模型相比,GGM模型与格网化船测水深模型的差值的标准差达到了37.10m。     

基于T/P卫星海面测高的黄东海海面地形变化探讨

利用Topex/Posedion卫星的SSHA数据对黄、东海1993-2001年期间的平均海面地形的空间形态特征、变化速率的空间分布特征及年内变化特征等3个方面进行了分析.研究结果表明,该海区9a平均海面地形的基本特征为：东南高、西北低,由东南向西北倾斜,最大高差超过90 cm;1993-2001年期间全海区均呈现海面上升趋势,上升速率值在5～8.6 mm/a之间,海面上升的空间分异表现为南快北慢,东快西慢.海面地形的年内变化在时间上呈正弦波动,空间上中、北部区域变化速度快,年较差大;南部区域变化速度慢,年较差小;变化空间特征复杂.     

卫星重力梯度测量在海洋科学中的应用分析

简述了卫星重力梯度测量技术的基本原理和GOCE数据特点;基于三个不同的重力场模型,采用不同阶次,联合卫星测高平均海面高模型分别推算出全球海面地形,并对结果作了比较分析;探讨了卫星重力梯度测量技术在海洋科学各相关领域的具体应用前景,指出卫星重力梯度测量技术的发展将为海洋科学发展带来巨大的变化。     

中国近海海面地形及形成机制研究

用几何水准法、水文法、重力—卫星测高法三种不同方法求得了中国近海海面地形,给出了中国近海海面地形数学模型和中国近海海面地形图,探讨了中国近海海面地形形成机制,包括海洋水文因素、大气压力影响,以及太平洋北赤道流的影响。     

利用卫星测高资料确定全球海洋重力场

详细描述了卫星测高数据的平滑处理、高斯低通滤波、交叉点剩余垂线偏差计算、网格化方法以及根据逆的威宁·曼尼兹公式利用 1DFFT技术反演海域重力异常的解算过程 ,介绍一种确定正常轨道地面轨迹交叉点位置的简便方法 ,导出了海面地形对垂线偏差影响的改正公式以及剩余网格垂线偏差模型值的计算公式。所确定的全球 82°S～ 82°N ,0°～ 36 0°海域 30′× 30′网格平均重力异常与船测平均重力异常比较表明 ,精度达到± 4 .1～± 4 .7毫伽。     

Impact of Ocean Mean Dynamic Topography on Satellite Data Assimilation

The response of an eddy-permitting ocean model to changes imposed by the use of different mean dynamic topographies (MDT) is analyzed in a multivariate assimilation context, allowing the evaluation of this impact, not only on the surface circulation, but also on the interior ocean representation. The assimilation scheme is a reduced-order sequential Kalman filter (SEEK). In a first set of experiments, high resolution sea surface temperature, along-track sea surface height and sea surface salinity from climatology are assimilated into a 1/3° resolution North and Tropical Atlantic version of the HYCOM model. In a second experiment, in situ profile data are assimilated in addition to the surface measurements.

The first set of experiments illustrates that important differences in the representation of the horizontal model circulation pattern are related to differences in the MDT used. The objective of assimilation is to improve the representation of the 3D ocean state. However, the imperfect representation of the mean dynamic topography appears to be an important limiting factor with regard to the degree of realism obtained in the simulated flow.

Vertical temperature and salinity profiles are key observations to drive a general circulation ocean model toward a more realistic state. The second set of experiments shows that assimilating them in addition to sea surface measurements is a far from trivial exercise. A specific difficulty is due to inconsistencies between the dynamic topography diagnosed from in situ observations and that diagnosed from sea surface height. These two fields obtained from different data sources do not contain exactly the same information. In order to overcome this difficulty, a strategy is proposed and validated.     

Impact of Ocean Mean Dynamic Topography on Satellite Data Assimilation

The response of an eddy-permitting ocean model to changes imposed by the use of different mean dynamic topographies (MDT) is analyzed in a multivariate assimilation context, allowing the evaluation of this impact, not only on the surface circulation, but also on the interior ocean representation. The assimilation scheme is a reduced-order sequential Kalman filter (SEEK). In a first set of experiments, high resolution sea surface temperature, along-track sea surface height and sea surface salinity from climatology are assimilated into a 1/3° resolution North and Tropical Atlantic version of the HYCOM model. In a second experiment, in situ profile data are assimilated in addition to the surface measurements.

The first set of experiments illustrates that important differences in the representation of the horizontal model circulation pattern are related to differences in the MDT used. The objective of assimilation is to improve the representation of the 3D ocean state. However, the imperfect representation of the mean dynamic topography appears to be an important limiting factor with regard to the degree of realism obtained in the simulated flow.

Vertical temperature and salinity profiles are key observations to drive a general circulation ocean model toward a more realistic state. The second set of experiments shows that assimilating them in addition to sea surface measurements is a far from trivial exercise. A specific difficulty is due to inconsistencies between the dynamic topography diagnosed from in situ observations and that diagnosed from sea surface height. These two fields obtained from different data sources do not contain exactly the same information. In order to overcome this difficulty, a strategy is proposed and validated.     

Mean Dynamic Topography and Geostrophic Surface Currents in the Fram Strait Derived from Geodetic Data

Two mean dynamic topography (MDT) fields are determined in the Fram Strait between Svalbard and Greenland. New airborne gravity anomalies, older data, and two different mean sea surface (MSS) fields are combined using the least squares collocation (LSC) technique. The results are compared to an oceanographic MDT model and two synthetic MDT fields. The same main currents are seen in all fields. Additionally, smaller scale features are revealed in the new MDT fields. Geostrophic surface currents derived from the MDT models are compared to moorings and Lagrangian drifters. The agreement is desultory. The oceanographic data are an inadequate basis of comparison due to data gaps. Nevertheless, it is the only one available.     

Improving the Coastal Mean Dynamic Topography by Geodetic Combination of Tide Gauge and Satellite Altimetry

Abstract

The ocean mean dynamic topography (MDT) is the surface representation of the ocean circulation. The MDT may be determined by the ocean approach, which involves temporal averaging of numerical ocean circulation model information, or by the geodetic approach, wherein the MDT is derived using the ellipsoidal height of the mean sea surface (MSS), or mean sea level (MSL) minus the geoid as the geoid. The ellipsoidal height of the MSS might be estimated either by satellite or coastal tide gauges by connecting the tide gauge datum to the Earth-centred reference frame. In this article we present a novel approach to improve the coastal MDT, where the solution is based on both satellite altimetry and tide gauge data using new set of 302 tide gauges with ellipsoidal heights through the SONEL network. The approach was evaluated for the Northeast Atlantic coast where a dense network of GNSS-surveyed tide gauges is available. The typical misfit between tide gauge and satellite or oceanographic MDT was found to be around 9?cm. This misfit was found to be mainly due to small scale geoid errors. Similarly, we found, that a single tide gauge places only weak constraints on the coastal dynamic topography.     

Predicting Global Seafloor Topography Using Multi-Source Data

A new one-minute global seafloor topography model was derived from vertical gravity gradient anomalies (VGG), altimetric gravity anomalies, and ship soundings. Ship soundings are used to constrain seafloor topography at wavelengths longer than 200 km and to calibrate the topography to VGG (or gravity) ratios at short wavelengths area by area. VGG ratios are used to predict seafloor topography for wavelength bands of 100–200 km and to suppress the effect of crust isostasy. Gravity anomalies are used to recover seafloor topography at wavelengths shorter than 100 km. The data processing procedure is described in detail in this paper. The accuracy of the model is evaluated using ship soundings and existing models, including General Bathymetric Charts of the Oceans (GEBCO), DTU10, ETOPO1, and SIO V15.1. The results show that, in the discussed regions, the accuracy of the model is better than ETOPO1, GEBCO, and DTU10. Additionally, the model is comparable with V15.1, which is generally believed to have the highest accuracy. In the north-central Pacific Ocean, the accuracy of the model increased by approximately 29.5% compared with the V15.1 model. This indicates that a more accurate seafloor topography model can be formed by combining gravity anomalies, VGG, and ship soundings.     

A New Methodology for Incorporating Tide Gauge Data in Sea Surface Topography Models

As part of the Vertical Offshore Reference Frames (VORF) project sponsored by the U. K. Hydrographic Office, a new model for Sea Surface Topography (SST) around the British Isles has been developed. For offshore areas (greater than 30 km from the coast), this model is largely derived from satellite altimetry. However, its accuracy and level of detail have been enhanced in coastal areas by the inclusion of not only the 60 PSMSL tide gauges with long-term records around the coasts of the United Kingdom and Ireland but also some 385 gauges established at different epochs and for different observation spans by the U. K. Admiralty. All tide gauge data were brought into a common reference frame by a combination of datum models and direct GPS observations, but a more significant challenge was to bring all short-term sea level observations to an unbiased value at a common epoch. This was achieved through developing a spatial-temporal correlation model for the variations in mean sea level around the British Isles, which in turn meant that gauges with long-term observation spans could be used as control points to improve the accuracy of Admiralty gauges. It is demonstrated that the latter can contribute point observations of mean sea level (MSL) with a precision of 0.078 m. A combination of least squares collocation and interpolation was developed to merge the coastal point and offshore gridded data sets, with particular algorithms having to be developed for different configurations of coastal topology. The resulting model of sea surface topography is shown to present a smooth transition from inshore coastal areas to offshore zones. Further benefits of the techniques developed include an enhanced methodology for detecting datum discontinuities at permanent tide gauges.     

Effect of the Mean Dynamic Topography on the Geoid-to-Quasigeoid Separation Offshore

It is commonly acknowledged that offshore the quasigeoid very closely coincides with the geoid. Nevertheless, the numerical assessment supporting this assumption has not yet been provided. Moreover, the rigorous definition of the quasigeoid surface and consequently the geoid-to-quasigeoid separation offshore is not given in geodetic literature. To address these issues, we define in this study the quasigeoid surface offshore in the context of the mean sea level. We then derive the spectral expressions for computing the geoid-to-quasigeoid separation offshore and apply these expressions estimate the vertical separation between the geoid and the quasigeoid over the world's oceans and marginal seas using the global dataset of the DTU15 mean dynamic topography. By taking the analogy of defining the geoid-to-quasigeoid separation inland by means of the disturbing potential differences of values evaluated on the geoid and at the topographic surface, the computation offshore is practically realized from values of the disturbing potential on the geoid and at the mean sea surface. Our result shows that the geoid-to-quasigeoid separation offshore is completely negligible, with most of the values within the interval ±0.3 mm.     

Analysis of Dynamic Stability of Ocean Gravity Structure Foundations

Based on unified equivalent harmonic loading on seabed foundation and energy approach suggested by the authors, the development of dynamic pore water pressure and stability of soil foundation for the vibration of ocean gravity structures excited by random wave loading are analysed. It may be seen that the present method for the study of dynamic problems of ocean gravity structure soil foundations is more reasonable and convenient.     

利用验潮站数据进行三种潮汐模型的精度分析

采用全球分布的565个验潮站水位资料对NAO.99b,CSR4.0和TPXO7.2三种潮汐模型进行精度评估。结果表明:在全球海洋范围内,NAO.99b模型精度最高;在黄海海域,TPXO7.2模型的精度最高;在东海和南海海域,则是NAO.99b模型最优;在深海海域,三种模型精度差异不大;在浅海海域,采用同化方法的潮汐模型比采用经验方法的潮汐模型更有优势。