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1.
Yan Ming Wang 《Marine Geodesy》2013,36(4):251-258
Historically, prediction of ocean floor depth, or bathymetry, has been based on the isostatic modeling and linearized relationships between gravity anomalies and bathymetry. The need for isostatic modeling limits the application of the resulting bathymetry predictions as constraints in geophysical models. An alternative technique making use of the Earth's vertical gravity gradient for predicting bathymetry is explored in this paper. This technique is based on the fact that the observed gravity gradient anomalies result primarily from local mass concentrations on the ocean floor, and that mass compensation by the oceanic crust has an insignificant effect on the gravity gradients, and can be neglected. The resulting bathymetry prediction therefore is independent of isostatic modeling assumptions, allowing it to be used as a constraint on models of lithospheric compensation and for other geodetic and geophysical applications. 相似文献
2.
Spectral analysis techniques have been applied to data sets of gravity and topography selected across fracture zones with large offset in the Equatorial and Central Atlantic Ocean and processed independently for each fracture zone. Three simple compensation models, two in local isostatic equilibrium (Airy I and II) and one in regional equilibrium (Plate model) have been tested. It is found that the free-air anomalies are primarily controlled by the topography and its isostatic response. For short wavelengths, admittance can be explained either by the effect of uncompensated sea floor topography with high density basement or by the effect of uncompensated sea floor topography with normal oceanic basement density but accompanied by a crust of constant thickness. For intermediate wavelengths, admittance for the Romanche fracture zone agrees best with a local isostatic model in which compensation is achieved by a less dense material in the upper mantle. No such evidence exists for the Vema and Chain fracture zones for which topography could just as well be regionally supported by an elastic plate 3 to 10 km thick. For longer wavelengths, the admittances computed for the three fracture zones are compatible with a thermal compensation of the topography. 相似文献
3.
INTRODUCTION' Regional isostatic model(Vening Meinesz, 1941 )considered the lithosphere as a loaded elasticplate floating on astherosphere, and the topographical load was supPOrted by elastic stress of theplate, then compensation would be accomplished in a wider regional extent. When the thicknessof elastic plate is certain, the increase of topographic load will cause the elastic plate to be downward fie-cure and the crust thickened. The isostatic resPOnse function, i. e. experimental i… 相似文献
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5.
基于水下自主航行器(AUV)的神狐峡谷谷底块体搬运沉积特征及其对深水峡谷物质输运过程的指示 总被引：2，自引：0，他引：2
海底峡谷是陆源物质向深海运移的重要通道。对于远离陆地的海底峡谷,通常认为浊流是物质搬运的主要营力。受限于探测精度和复杂作业环境影响,使用常规地球物理资料对深水海底峡谷尤其是对谷底沉积体的形态和结构特征的刻画不够精细。基于水下自主航行器(AUV,Autonomous Underwater Vehicle)采集的高分辨率多波束、旁扫声呐和浅地层剖面资料,对神狐峡谷群中的一条峡谷的谷底表面及部分浅部地层的沉积特征进行了分析。结果表明,峡谷谷底浅部地层并不像它平滑的表面那么简单,而是由大量内部杂乱弱反射、厚度在8.4 m及以下的块体搬运沉积体组成。峡谷中下游块体搬运沉积体大都沿峡谷走向整体呈条带状展布,不是直接来源于相邻的峡谷脊部。研究认为在特定沉积环境下(例如高海平面时期),陆坡限定性峡谷谷底的块体搬运沉积过程的重复进行是峡谷谷底物质输运的重要途径,与浊流共同雕刻了峡谷的地形地貌。基于AUV的地球物理探测技术将是研究海底浅表层沉积过程和保障海底工程施工的重要手段。 相似文献
6.
冲绳海槽海底地形的补偿模式初步研究 总被引：1，自引：1，他引：1
从区域补偿模式和实验均衡理论出发,利用重力和地形资料计算了冲绳海槽的均衡响应函数,结果表明：冲绳海槽南段弹性板有效厚度和补偿深度明显大于中段,结合其它地质地球物理资料解释认为,产生这种差异的原因主要是南,中两段岩石圈温度和补偿机制的不同所致。 相似文献
7.
利用高分辨率水深、重力、地磁和多道反射地震数据,综合分析了楚科奇边缘地及其周边区域的地形地貌和地球物理场特征,划分了区域构造单元。研究表明,楚科奇边缘地不仅是楚科奇大陆架外缘独特的地形单元,也是一个相对独立的构造单元,与周边的加拿大洋盆、阿尔法-门捷列夫大火山岩省、北楚科奇陆架盆地和阿拉斯加被动陆缘等构造单元在地球物理场和区域构造上具有截然不同的特征。楚科奇边缘地是一个地壳减薄的微陆块,新生代早、中期发生了大规模的E-W向构造拉伸作用,基底断块的差异性升降塑造了当前的地形地貌和沉积层的发育。边缘地可能形成于北楚科奇盆地侏罗纪-早白垩纪的张裂作用,而内部盆-脊相间排列的构造格局则可能与加拿大海盆相边缘地俯冲作用停止后的均衡调整有关。 相似文献
8.
Though ubiquitous in the global oceans, double diffusive mixing has been largely ignored or poorly represented in the models of turbulent mixing in the ocean and in 3-D ocean models, until recently. Salt fingers occur in the interior of many marginal seas and ocean basins, the Tyrrhenian Sea and the subtropical Atlantic being two examples. Diffusive convection type of double diffusion occurs in the upper layers of many sub-polar seas and polar oceans due to cold melt water from sea ice. Consequently, it is important to be able to properly parameterize double diffusive mixing in basin scale and global ocean models, so that the water mass structure in the interior of the ocean can be properly simulated. This note describes a model for double diffusive mixing in the presence of background shear, based on Mellor–Yamada type second moment closure, more specifically Kantha, 2003, Kantha and Clayson, 2004 second moment closure models of resulting turbulence, following Canuto et al. (2008a) but employing a different strategy for modeling the pertinent terms in the second moment equations. The resulting model is suitable for inclusion in ocean general circulation models. 相似文献
9.
G.J. Gorman M.D. Piggott C.C. Pain C.R.E. de Oliveira A.P. Umpleby A.J.H. Goddard 《Ocean Modelling》2006,12(3-4):436-452
A method for generating high quality unstructured computational meshes for applications in geophysical, and specifically ocean, modelling is presented. The method generates a three-dimensional mesh which is optimised to approximate the bathymetry to a user-specified accuracy, which itself may be defined as a function of space and bathymetry. To do this a mesh optimisation method is employed which allows the formation of highly anisotropic elements aligned with bathymetric variations of high curvature. In addition a coastal recovery algorithm, based upon feature decimation and edge recovery, is described. 相似文献
10.
Abstract The contribution of bathymetry to the estimation of gravity field related quantities is investigated in an extended test area in the Mediterranean Sea. The region is located southwest of the island of Crete, Greece, bounded between 33? ≤ ? ≤ 35? and 15? ≤ λ ≤ 25?. Gravity anomalies from the KMS99 gravity field and shipborne depth soundings are used with a priori statistical characteristics of depths in a least-squares collocation procedure to estimate a new bathymetry model. Two different global bathymetry models, namely JGP95E and Sandwell and Smith V8, are used to derive the depth a priori statistical information, while the estimated model is compared against both the global ones and the shipborne depth soundings to assess whether there is an improvement. Various marine geoid models are estimated using ERS1 and GEOSAT Geodetic Mission altimetry and shipborne gravity data. In that process, the effect of the bathymetry is computed using both the estimated and the original depths through a residual terrain modeling reduction. The TOPEX/Poseidon Sea Surface Heights, known for their high accuracy and precision, and the GEOMED solution for the geoid in the Mediterranean are used as control for the validation of the new geoid models and to assess the improvement that the estimated depths offer to geoid modeling. The results show that the newly estimated bathymetry agrees better (by about 30 to 300 m) with the shipborne depth soundings and provides smoother residual geoid heights and gravity anomalies (by about 8–20%) than those from global models. Finally, the achieved accuracy in geoid modeling ranges between 6 and 10 cm (1σ). 相似文献
11.
The contribution of bathymetry to the estimation of gravity field related quantities is investigated in an extended test area in the Mediterranean Sea. The region is located southwest of the island of Crete, Greece, bounded between 33ˆ ≤ ϕ ≤ 35ˆ and 15ˆ ≤ λ ≤ 25ˆ. Gravity anomalies from the KMS99 gravity field and shipborne depth soundings are used with a priori statistical characteristics of depths in a least-squares collocation procedure to estimate a new bathymetry model. Two different global bathymetry models, namely JGP95E and Sandwell and Smith V8, are used to derive the depth a priori statistical information, while the estimated model is compared against both the global ones and the shipborne depth soundings to assess whether there is an improvement. Various marine geoid models are estimated using ERS1 and GEOSAT Geodetic Mission altimetry and shipborne gravity data. In that process, the effect of the bathymetry is computed using both the estimated and the original depths through a residual terrain modeling reduction. The TOPEX/Poseidon Sea Surface Heights, known for their high accuracy and precision, and the GEOMED solution for the geoid in the Mediterranean are used as control for the validation of the new geoid models and to assess the improvement that the estimated depths offer to geoid modeling. The results show that the newly estimated bathymetry agrees better (by about 30 to 300 m) with the shipborne depth soundings and provides smoother residual geoid heights and gravity anomalies (by about 8-20%) than those from global models. Finally, the achieved accuracy in geoid modeling ranges between 6 and 10 cm (1σ). 相似文献
12.
Christian Hirt 《Marine Geodesy》2013,36(2):183-202
We apply the residual terrain modeling (RTM) technique for gravity forward-modeling to successfully improve high-resolution global gravity fields at short spatial scales in coastal zones. The RTM scheme is combined with the concept of rock-equivalent topography, allowing to use a single uniform constant mass-density in the RTM forward-modeling, both at land and sea. SRTM30_PLUS bathymetry is merged with higher-resolution SRTM V4.1 land topography, and expanded into spherical harmonics to degree 2160, yielding a new and consistent high-degree RTM reference surface. The forward-modeling performance is demonstrated in coastal zones of Greece and Canada using ground-truth vertical deflections, gravity from land and shipborne gravimetry, and geoid heights from GPS/leveling, with improvements originating from bathymetry clearly identified. We demonstrate that the SRTM30_PLUS bathymetry carries information on gravity field structures at spatial scales less than 5 arc minutes, which can be used to augment EGM2008 in (rugged) coastal zones, both over land and marine areas. This may be of value (i) to partially reduce the signal omission error in EGM2008/GOCE-based height transfer in areas devoid of dense gravity data, (ii) to fill the gap between land gravity and shipborne gravity along rugged coastlines, and (iii) for the development of next-generation altimetric gravity fields. 相似文献
13.
M. E. Artemjev T. M. Babaeva V. O. Mikhailo I. E. Voydetsky 《Marine Geophysical Researches》1984,7(1-2):129-148
All anomalous masses of the Earth are reflected in the free air gravity anomalies and the geoidal undulations. The low viscosity
of the asthenosphere significantly reduces the possibility of existence of density inhomogeneities in the layer. This fact
provides some physical basis for the separation of the gravity field anomalies. It has been shown by power spectrum analysis
of the free air anomalies and gravity field of isostatically compensated model of the lithosphere for the North Atlantic and
adjacent areas of America, Europe and Mediterranean, that the attraction of isostatically compensated model is significant
for any wave length of the field. It causes significant error in the interpretation if long wavelength constituents of the
free air gravity anomalies are considered as a field of deep anomalous masses. The isostatic anomalies und isostatic geoid
are free from the influences of isostatically compensated lithosphere. The characteristic feature of the isostatic anomalies
power spectrum is a pronounced minimum at the wavelength of about 1000 km. The relative homogeneity of the asthenosphere may
explain this minimum. It means that principal density inhomogeneities of the Earth's interior are separated by the asthenospheric
layer. Such a minimum has not been observed at the power spectrum of free air anomalies being masked by corresponding wavelength
of the field of isostatically compensated lithosphere. Isostatic anomalies that reflect the differences between the real structure
of the lithosphere and its isostatically compensated model have wavelengths less than 1000 km. Isostatic anomalies with the
wavelength more than 1000 km reflect the attraction of density inhomogeneities situated under the level of isostatic compensation.
The basic features of power spectrum of isostatic anomalies are the same for oceanic and continental areas. The method based
on Kolmogorov-Wiener filtration which consideres statistical characteristics of the field has been developed to divide the
isostatic gravity anomalies into lithosphere and mantle components. For the North Atlantic and adjacent areas the field of
mantle inhomogeneities has been determined. 相似文献
14.
《Ocean Modelling》2010,31(4):310-322
A global spectral barotropic ocean model is introduced to describe the depth-averaged flow. The equations are based on vorticity and divergence (instead of horizontal momentum); continents exert a nearly infinite drag on the fluid. The coding follows that of spectral atmospheric general circulation models using triangular truncation and implicit time integration to provide a first step for seamless coupling to spectral atmospheric global circulation models and an efficient method for filtering of ocean wave dynamics. Five experiments demonstrate the model performance: (i) Bounded by an idealized basin geometry and driven by a zonally uniform wind stress, the ocean circulation shows close similarity with Munk’s analytical solution. (ii) With a real land–sea mask the model is capable of reproducing the spin-up, location and magnitudes of depth-averaged barotropic ocean currents. (iii) The ocean wave-dynamics of equatorial waves, excited by a height perturbation at the equator, shows wave dispersion and reflection at eastern and western coastal boundaries. (iv) The model reproduces propagation times of observed surface gravity waves in the Pacific with real bathymetry. (v) Advection of tracers can be simulated reasonably by the spectral method or a semi-Langrangian transport scheme. This spectral barotropic model may serve as a first step towards an intermediate complexity spectral atmosphere–ocean model for studying atmosphere–ocean interactions in idealized setups and long term climate variability beyond millennia. 相似文献
15.
潜艇在水下进行重力梯度探测与导航过程中,利用重力梯度仪测量所在位置的重力梯度张量来感知周边海底地形起伏以及规避障碍物,由于潜艇中人员具有一定的质量,人员在理论上会对重力梯度测量值产生影响。为分析人员质量对重力梯度测量的影响,将人体简化为立方体模型,计算人体在潜艇内不同高度处的重力梯度异常分布情况,分析其对重力梯度探测的影响,并将计算得到的结果与质点模型的结果对比分析得到两者的差异。结果表明在距离人体5 m以内的大部分位置上,重力梯度各分量的量级能达到10~(-2)E,在更近的位置上梯度值的量级能达到10E,为防止对重力梯度仪测量结果产生影响,人员需要在距离梯度仪一定的距离外活动,随着精度的提高,限制距离将会增大。本文得出的结论可为以后重力梯度探测工程化应用提供一定的理论参考。 相似文献
16.
O. F. Vasil’ev O. F. Voropaeva A. F. Kurbatskii 《Izvestiya Atmospheric and Oceanic Physics》2011,47(3):265-280
Specific features of the turbulent transfer of the momentum and heat in stably stratified geophysical flows, as well as possibilities for including them into RANS turbulence models, are analyzed. The momentum (but not heat) transfer by internal gravity waves under conditions of strong stability is, for example, one such feature. Laboratory data and measurements in the atmosphere fix a clear dropping trend of the inverse turbulent Prandtl number with an increasing gradient Richardson number, which must be reproduced by turbulence models. Ignoring this feature can cause a false diffusion of heat under conditions of strong stability and lead, in particular, to noticeable errors in calculations of the temperature in the atmospheric boundary layer. Therefore, models of turbulent transfer must include the effect of the action of buoyancy and internal gravity waves on turbulent flows of the momentum. Such a strategy of modeling the stratified turbulence is presented in the review by a concrete RANS model and original results obtained during the modeling of stratified flows in the environment. Semiempirical turbulence models used for calculations of complex turbulent flows in deep stratified bodies of water are also analyzed. This part of the review is based on the data of investigations within the framework of the large international scientific Comparative Analysis and Rationalization of Second-Moment Turbulence Models (CARTUM) project and other publications of leading specialists. The most economical and effective approach associated with modified two-parameter turbulence models is a real alternative to classical variants of these models. A class of test problems and laboratory and full-scale experiments used by the participants of the CARTUM project for the approbation of numerical models are considered. 相似文献
17.
Abstract Marine positioning is relevant for several aspects of tsunami research, observation, and prediction. These include accurate positioning of instruments on the ocean bottom for determining the deep‐water signature of the tsunami, seismic observational setups to measure the earthquake parameters, equipment to determine the tsunami characteristics during the propagation phase, and instruments to map the vertical uplift and subsidence that occurs during a dip‐slip earthquake. In the accurate calculation of coastal tsunami run‐up through numerical models, accurate bathymetry is needed, not only near the coast (for tsunami run‐up) but also in the deep ocean (for tsunami generation and propagation). If the bathymetry is wrong in the source region, errors will accumulate and will render the numerical calculations inaccurate. Without correct and detailed run‐up values on the various coastlines, tsunami prediction for actual events will lead to false alarms and loss of public confidence. 相似文献
18.
A global spectral barotropic ocean model is introduced to describe the depth-averaged flow. The equations are based on vorticity and divergence (instead of horizontal momentum); continents exert a nearly infinite drag on the fluid. The coding follows that of spectral atmospheric general circulation models using triangular truncation and implicit time integration to provide a first step for seamless coupling to spectral atmospheric global circulation models and an efficient method for filtering of ocean wave dynamics. Five experiments demonstrate the model performance: (i) Bounded by an idealized basin geometry and driven by a zonally uniform wind stress, the ocean circulation shows close similarity with Munk’s analytical solution. (ii) With a real land–sea mask the model is capable of reproducing the spin-up, location and magnitudes of depth-averaged barotropic ocean currents. (iii) The ocean wave-dynamics of equatorial waves, excited by a height perturbation at the equator, shows wave dispersion and reflection at eastern and western coastal boundaries. (iv) The model reproduces propagation times of observed surface gravity waves in the Pacific with real bathymetry. (v) Advection of tracers can be simulated reasonably by the spectral method or a semi-Langrangian transport scheme. This spectral barotropic model may serve as a first step towards an intermediate complexity spectral atmosphere–ocean model for studying atmosphere–ocean interactions in idealized setups and long term climate variability beyond millennia. 相似文献
19.
使用BEDMAP2关于南极大陆及周围海域和JGP95E关于全球表面高程、冰厚和冰下及水深地形数据,采用球坐标系下的扇形球壳块重力效应公式,在极方位投影直角坐标网格节点上计算了南极大陆及周围海域的近区及远区的地形和艾黎均衡重力效应。南极大陆冰盖带来可观的正重力效应,南大洋负重力效应又影响到了南极内陆,全球地形/均衡重力效应与局部地形高低有关联性,而低负值区主要分布在环南极的陆坡。获得的约1n mile间距的地形和艾黎均衡重力效应网格数据可用于南极大陆及周边海域的重力改正,提供准确、一致的布格重力异常和艾黎均衡重力异常。 相似文献
20.
Enderby Land in East Antarctica and its adjacent areas, which are closely related to the Indian Plate in their geological evolution, have become one of the key zones for studies on how the Antarctic continent evolves. Based on the isostasy and flexure theories of the lithosphere and using the CRUST1.0 model as the depth constraint, this paper uses the gravity field model EIGEN-6C4 and topographic data to calculate the isostatic gravity anomalies of Enderby Land and its adjacent areas. Then, the ... 相似文献