Global detailed geoid computation and model analysis     

James G. Marsh  Samir Vincent 《Surveys in Geophysics》1974,1(4):481-511

This paper presents a survey of recent work on the gravimetric geoid. The gravity models considered are those published in the past few years by the Goddard Space Flight Center (GSFC), the Smithsonian Astrophysical Observatory (SAO) and the Ohio State University (OSU). Comparisons and analyses have been carried out through the ose of detailed gravimetric geoids which we have computed by combining the above-mentioned models with a set of 26 000, 1^ox1^o mean free air gravity anomalies. The accuracy of the detailed gravimetric geoid computed using the most recent Goddard Earth Model (GEM-6) in conjunction with the set 1^ox1^o mean free air gravity anomalies is assessed at 2 m on the continents of North America, Europe And Australia, 2 to 5 m in the North-East Pacific and North Atlantic areas and 5 to 10 m in other areas where surface gravity data are sparse. Rms differences between this detailed geoid and the detailed geoids computed using the other satellite gravity fields in conjunction with same set of surface data range from 3 to 7 m. The maximum differences in all cases occurred in the Southern Hemisphere where surface data and satellite observations are sparse. These differences exhibited wavelengths of approximately 30^o to 50^o in longitude. Detailed geoidal heights were also computed with models truncated to 12th degree and order as well as 8th degree and order. This truncation resulted in a reduction of the rms differences to a maximum of 5 m. Comparisons have been made with the astrogeodetic data of Rice (United States), Bomford (Europe), and Mather (Australia) and also with geoidal heights from satellite solutions for geocentric station coordinates in North America and the Caribbean.  相似文献   

Oligocene uplift of the Western Greater Caucasus: an effect of initial Arabia–Eurasia collision     

Stephen J. Vincent  Andrew C. Morton  Andrew Carter  Samantha Gibbs  Teimuraz G. Barabadze 《地学学报》2007,19(2):160-166

The Greater Caucasus is Europe's largest mountain belt. Significant uncertainties remain over the evolution of the range, largely due to a lack of primary field data. This work demonstrates that depositional systems within the Oligocene–Early Miocene Maykop Series on either side of the Western Greater Caucasus (WGC) display a similar provenance and divergent palaeocurrents away from the range, constraining a minimum age for the subaerial uplift of the range as early Early Oligocene. An Eocene–Oligocene hiatus, basal Oligocene olistostromes and a marked increase in nannofossil reworking also point to initial deformation in the earliest Oligocene. The initial uplift of the WGC occurred during the final assembly of the Tethysides to its south. Uplift commenced after the Late Eocene final suturing of northern Neotethys and during the initial collision of Arabia with the southern accreted margin of Eurasia. This suggests that compressional deformation was rapidly transferred across the collision zone from the indenting Arabian plate to its northern margin.  相似文献   

The spin and shape of dark matter haloes in the Millennium simulation of a Λ cold dark matter universe     

Philip Bett  Vincent Eke  Carlos S. Frenk  Adrian Jenkins  John Helly  Julio Navarro 《Monthly notices of the Royal Astronomical Society》2007,376(1):215-232

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Roughness length in the turbulent Ekman layer above the sea bed     

C.E. Vincent  J.G. Harvey 《Marine Geology》1976,22(3):M75-M81

Roughness lengths were determined from average current profiles in the logarithmic boundary layer at a site in the southern North Sea. Grab samples indicated that the bed configuration controlling the bed roughness was unlikely to change even at maximum spring tides, but the measured roughness lengths were found to decrease as the speed of the flow 10 m above the bed increased. This has been qualitatively interpreted in terms of the size of the turbulent eddies within the flow and their effectiveness at “feeling” the size of the elements forming the bed roughness. It is also shown that the dependence of the observed drag coefficient on the Rossby number follows closely the theoretical form when the roughness length decreases with increasing flow speed.  相似文献   

Systematic marine conservation planning in data-poor regions: Socioeconomic data is essential   总被引：1，自引：0，他引：1  

Natalie C. Ban  Gretchen J.A. Hansen  Michael Jones  Amanda C.J. Vincent   《Marine Policy》2009,33(5):794-800

Systematic planning for conservation is highly regarded but relies on spatially explicit data that are lacking in many areas of conservation concern. The decision support tool Marxan is applied to a reef system in the central Philippines where 30 marine protected areas (MPAs) have been established in communities without much use of biophysical data. The intent was to explore how Marxan might assist with the legally required expansion to protect 15% of marine waters, and how existing MPAs might affect that process. Results show that biophysical information alone did not provide much guidance in identifying patterns of conservation importance in areas where the data are poor. Socioeconomic data were needed to distinguish among possible areas for protection; but here, as elsewhere in marine environments, the availability of such data was very limited. In the final analysis, local knowledge and integrated understanding of socioeconomic realities may offer the best spatially explicit information. The 30 existing MPAs, which encompassed a small proportion of the reef system, did not limit future options in developing a suite of MPAs on a broader scale. Rather, they appeared to generate the support for MPAs that is obligatory for any larger zoning effort. In summary, establishing MPAs based on community-driven criteria has biological and social value, but efforts should be made to collect ecological and socioeconomic data to guide the continued creation of MPAs.  相似文献   

Partially standing wave measurement in the presence of steady current by use of coincident velocity and/or pressure data     

Déborah Drevard  Vincent ReyPhilippe Fraunié 《Coastal Engineering》2009

In recent years, instrumentation for field flow measurements has become more and more sophisticated. In particular, local pressure and velocity are measured at frequency rates up to at least 2 Hz, which gives information on wave energy. The present work describes the methods for partially standing wave measurement in the presence of current by use of coincident measurements of both horizontal velocity and pressure, or vertical velocity. Reflection calculated from either coincident horizontal and vertical velocities or three-gauge methods are compared. They are based on existing experiments carried out in an ocean wave basin for both regular and irregular waves in the presence of current. Applications to field measurements, out of and in the breaking zones are then presented. In the nearshore, coincident horizontal and vertical velocities far from the bottom, and coincident horizontal velocity and pressure close to the bottom give relevant information concerning partially standing waves.  相似文献   

Analysis of the evolution of road tunnels equilibrium conditions with a convergence–confinement approach     

Federica Sandrone  Vincent Labiouse 《Rock Mechanics and Rock Engineering》2010,43(2):201-218

Since both lining structure and rock mass exhibit delayed behaviour, tunnel equilibrium conditions evolve with time. After discussing existing work done on different aspects of long-term tunnel behaviour, the aim of this paper is to “understand” the influence of rock mass and lining degradations on the long-term stability conditions of the tunnel by means of the convergence–confinement method. In order to represent the effects of degradation on tunnel long-term conditions, specific degradation models are selected according to the disorders identified during principal inspections of road tunnels in Switzerland. By simulating the reduction of the mechanical properties of both the rock mass and the lining or by using creep models, it is possible to assess the influence of the main degradation processes on tunnel stability. The results are interpreted in terms of tunnel safety factor. The presented approach for the determination of the long-term behaviour of tunnels, although valid for simple tunnel geometry and field stress conditions, allows to roughly estimate the influence of significant degradation processes that affect the rock mass and the supporting structure. Though this approach results in some simplification, it may be generalised and adopted with more refined numerical analyses for improving the assessment of tunnel long-term conditions.  相似文献   

The Decline and Restoration of a Coastal Lagoon (Lake Veere) in the Dutch Delta     

Sander Wijnhoven  Vincent Escaravage  Eugène Daemen  Herman Hummel 《Estuaries and Coasts》2010,33(6):1261-1278

The former tidal inlet Lake Veere was turned into a stagnant brackish lake in 1961. Ever since, the system has shown a continuous degradation. The current study shows the monitoring results for the macrozoobenthic communities and the abiotic conditions for the period 1990–2008. This includes the first step to remediation, the restoration of the exchange between the tidal marine Eastern Scheldt and Lake Veere in 2004. A continuous decline in water clearance co-occurring with decreasing macrofauna densities and richness was observed till 2004. Water quality (e.g., secchi depth, nutrient levels, and oxygen conditions) improved significantly after the measure at a higher salinity level with less variation. But the macrofauna densities, biomass, and diversity did not improve yet. First indications of changes in the benthic communities by arrival of new and returning species are however observed and show that restoration at macrofauna level follows the improved abiotic conditions with a delay of several years.  相似文献   

A roadmap for a dedicated Earth Science Grid platform     

Roberto Cossu  Monique Petitdidier  Julian Linford  Vincent Badoux  Luigi Fusco  Benoit Gotab  Ladislav Hluchy  Giuditta Lecca  Fabrizio Murgia  Camiel Plevier  Philippe Renard  Horst Schwichtenberg  Wim Som de Cerff  Viet Tran  Gerald Vetois 《Earth Science Informatics》2010,3(3):135-148

Due to its intensive data processing and highly distributed organization, the multidisciplinary Earth Science applications community is uniquely positioned for the uptake and exploitation of Grid technologies. Currently Enabling Grids for E-sciencE, and other large Grid infrastructures are already deployed and capable of operational services. So far however, the adoption and exploitation of Grid technology throughout the Earth Science community has been slower than expected. The Dissemination and Exploitation of GRids in Earth sciencE project, proposed by the European Commission to assist and accelerate this process in a number of different ways, had between its main goals the creation of a roadmap towards Earth Science Grid platform. This paper presents the resulting roadmap.  相似文献   

Sedimentary pigments as indicators of cyanobacterial dynamics in a hypereutrophic lake     

Bethany N. Deshpande  Roxane Tremblay  Reinhard Pienitz  Warwick F. Vincent 《Journal of Paleolimnology》2014,52(3):171-184

Lac Saint-Augustin is an urban lake located on the outskirts of Quebec City, one of North America’s oldest cities. Anthropogenic inputs from land clearing, agriculture, highway development and urbanization in the surrounding catchment have resulted in strong impacts on the limnology of the lake throughout the past three centuries. In recent years, this lake has experienced severe eutrophication, including persistent cyanobacterial blooms. In winter 2011, a sediment core was extracted from the deepest area of the lake. A detailed paleopigment analysis was used to assess eutrophication processes in the lake and to determine the timing and appearance of cyanobacterial blooms and their subsequent variability. Extracted chlorophyll a, its degradation products and 11 carotenoid pigments were identified and quantified via reverse-phase high performance liquid chromatography to examine relative changes in the phytoplankton. The results revealed large variations in the phytoplankton community structure of Lac Saint-Augustin over the past 356 years. Chlorophyll a concentrations per unit organic matter (OM) increased significantly from the base of the core to present day, rising more than 15-fold from 18.4 µg (g OM)^?1 at the base of the core to 287 µg (g OM)^?1 in the most recent strata. Biostratigraphical analysis revealed three major periods of enrichment, with episodes of cyanobacterial abundance from the 1890s onwards. The greatest changes occurred in the most recent period (from the 1960s to the present) relative to earlier periods, with pigment increases for all phytoplankton groups. The cyanobacterial pigments canthaxanthin, echinenone and zeaxanthin (also a marker for green algae) showed concentrations in the surface sediments that were significantly above values at the bottom of the core, and these differences were large, even giving consideration to the lesser pigment degradation near the surface. Overall, the results indicate that cyanobacterial blooms are not a recent feature of Lac Saint-Augustin but began to occur soon after catchment modification 150 years ago. The pigment records also imply that cyanobacterial and associated algal populations have risen to unprecedented levels over the last few decades of ongoing development of the Lac Saint-Augustin catchment. This study highlights the utility of multiple pigment analysis of lake sediments for identifying the timing and magnitude of anthropogenic impacts.  相似文献