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1.
Bishwajit Chakraborty Hans Werner Schenke Vijay Kodagali Rick Hagen 《Marine Geodesy》2002,25(1):19-26
Utilizing a hull-mounted, multinarrow beam echosounder onboard RV Polarstern, we measured variation of acoustic backscatter with incidence angles at two different sites in the Southern Oceans (Agulhas Plateau and the Riiser Larsen Sea). We modeled the data, using a composite roughness model, including water-sediment interface roughness and sediment volume roughness parameters. The model effectively uses the near normal incidence angle backscatter to determine the seafloor interface roughness parameters employing Helmholtz-Kirchhoff theory. Beyond 20° incidence angles, an application of Rayleigh-Rice theory is made by using a necessary splicing technique (combining both of the theories at 20° incidence angle). The estimated interface and volume roughness parameters are found to be in accordance with the known area geology. 相似文献
2.
Jörn Thiede Stephanie Pfirman Hans-Werner Schenke Wolfgang Reil 《Marine Geophysical Researches》1990,12(3):197-214
The sea floor of Fram Strait, the over 2500 m deep passage between the Arctic Ocean and the Norwegian-Greenland Sea, is part of a complex transform zone between the Knipovich mid-oceanic ridge of the Norwegian-Greenland Sea and the Nansen-Gakkel Ridge of the Arctic Ocean. Because linear magnetic anomalies formed by sea-floor spreading have not been found, the precise location of the boundary between the Eurasian and the North American plate is unknown in this region. Systematic surveying of Fram Strait with SEABEAM and high resolution seismic profiling began in 1984 and continued in 1985 and 1987, providing detailed morphology of the Fram Strait sea floor and permitting better definition of its morphotectonics. The 1984 survey presented in this paper provided a complete set of bathymetric data from the southernmost section of the Svalbard Transform, including the Molloy Fracture Zone, connecting the Knipovich Ridge to the Molloy Ridge; and the Molloy Deep, a nodal basin formed at the intersection of the Molloy Transform Fault and the Molloy Ridge. This nodal basin has a revised maximum depth of 5607 m water depth at 79°8.5N and 2°47E. 相似文献
3.
A new bathymetric model for the central Fram Strait 总被引:1,自引:0,他引:1
Based on data from R/V Polarstern multibeam sonar surveys between 1984 and 1997 high resolution bathymetry has been generated for the central Fram Strait. The area insonified covers approx. 36,500 km2 between 78–80°N and 0–7.5°E allowing the creation of a Digital Terrain Model (DTM) with 100 m grid spacing. The DTM was utilized for contouring and generation of a new series of bathymetric charts (AWI Bathymetric Charts of the Fram Strait, AWI BCFS) at a scale of 1:100,000. The paper starts with a brief introduction to the regional setting of the study area comprising information on the local links between bathymetry, sea ice transport and water mass exchange. The bathymetric feature names used in this article and how they were chosen is outlined. Next, the input data and processing applied are described. Thereafter the newly created grid and contour data are put into context with existing data sets. Finally the main bathymetric features of the area are characterized and the generated data products available for public disposal are specified. 相似文献
4.
Andreas?BeyerEmail author Rike?Rathlau Hans?Werner?Schenke 《Marine Geophysical Researches》2005,26(1):61-75
The Håkon Mosby Mud Volcano is a natural laboratory to study geological, geochemical, and ecological processes related to deep-water mud volcanism. High resolution bathymetry of the Håkon Mosby Mud Volcano was recorded during RV Polarstern expedition ARK XIX/3 utilizing the multibeam system Hydrosweep DS-2. Dense spacing of the survey lines and slow ship speed (5 knots) provided necessary point density to generate a regular 10 m grid. Generalization was applied to preserve and represent morphological structures appropriately. Contour lines were derived showing detailed topography at the centre of the Håkon Mosby Mud Volcano and generalized contours in the vicinity. We provide a brief introduction to the Håkon Mosby Mud Volcano area and describe in detail data recording and processing methods, as well as the morphology of the area. Accuracy assessment was made to evaluate the reliability of a 10 m resolution terrain model. Multibeam sidescan data were recorded along with depth measurements and show reflectivity variations from light grey values at the centre of the Håkon Mosby Mud Volcano to dark grey values (less reflective) at the surrounding moat. 相似文献
5.
A.C. Gebhardt W. Jokat F. Niessen J. Matthiessen W.H. Geissler H.W. Schenke 《Quaternary Science Reviews》2011,30(13-14):1726-1738
We present new evidence for a grounded ice sheet and subsequent erosion by large fields of coherent icebergs for the central and northern Yermak Plateau (80.6°N to 82.2°N). Sediment echosounder and swath bathymetry data were combined with seismic reflection profiles and reveal at least three different glacial events marked by erosional unconformities: (i) An erosional unconformity was observed at ~70–90 m below seafloor down to depths of more than 850 m present water depth, extending to ~82°N. The erosional unconformity is overlain by an acoustically chaotic layer of ~50 m thickness interpreted as a diamicton originating from a grounded ice sheet. The erosional unconformity and the overlying diamicton can be correlated to the overconsolidated sediments found at ODP Site 910 at a sediment depth between ~19 and 70–95 m. The oldest sediments just above the overconsolidated sediments are of late Early Pleistocene age (MIS19/20) and provide a minimum age for the grounding event. (ii) Parallel to sub-parallel mega-scale lineations are observed on large parts of the plateau west and northeast of the Sverdrup Bank at water depths between 725 and 850 m. These lineations are mainly oriented NNE-SSW and were quite likely formed by the keels of deep-draft, mega-scale tabular icebergs entrapped in a coherent mass of icebergs and sea ice. The lineations are of late Middle Pleistocene age. (iii) Smaller-scale curvilinear plow marks were found in the southernmost part of our study area at water depths between 640 and 775 m. These were possibly caused by single icebergs and are of Late Pleistocene age. Iceberg scours are also found on three basement heights on the Yermak Plateau. These, however, cannot be assigned to specific events; they might as well originate from additional glacial phases.The western (at >850 m water depth) and eastern (at >1000–1200 m water depth) flanks of the Yermak Plateau are relatively featureless, and indicate the maximum depth of a grounded ice sheet and of iceberg armadas probably entrapped in sea ice. 相似文献
6.
G. B. Udintsev N. A. Kurentsova A. F. Beresnev A. V. Kol’tsova L. G. Domoratskaya G. V. Schenke V. G. Bakhmutov V. D. Solov’ev 《Doklady Earth Sciences》2012,445(2):1029-1035
The relief and geophysical characteristics of the sea floor in the Drake Passage-Scotia Sea zone have been studied quite well in general. The oceanic floor within this zone is usually considered as a collage of small fragments of the continental bridge and of young oceanic plates formed by spreading under the large-scale motions of large lithospheric plates. The authors suppose an alternative version of the genesis of the Drake Passage-Scotia Sea lithospheric zone as an area of large fragments of the continental bridge subjected to basification under the conditions of temperate extension and local rifting. 相似文献
7.
G. Bohrmann C. Chin S. Petersen H. Sahling U. Schwarz-Schampera J. Greinert S. Lammers G. Rehder A. Daehlmann K. Wallmann S. Dijkstra H. -W. Schenke 《Geo-Marine Letters》1998,18(4):277-284
Hydrothermal activity in the Central Bransfield Basin revealed an active low-temperature vent field on top of a submarine volcanic structure. A temperature anomaly was detected and the sea floor showed various patches of white silica (opal-A) precipitate exposures and some yellow–brown Fe-oxyhydroxide crusts. Enriched dissolved methane concentrations were encountered. Sediment was near 24°C just after the grab came on deck. No dense population of chemosynthetically based macrofauna known from other hydrothermal venting areas was present, except for pogonophora. The observations suggest that the sedimented hydrothermal field at Hook Ridge is a low-temperature end-member branch from a deeper hydrothermal source. 相似文献
8.
9.
Andreas Beyer Bishwajit Chakraborty Hans Werner Schenke 《International Journal of Earth Sciences》2007,96(1):11-20
In this study multibeam angular backscatter data acquired in the eastern slope of the Porcupine Seabight are analysed. Processing
of the angular backscatter data using the ‘NRGCOR’ software was made for 29 locations comprising different geological provinces
like: carbonate mounds, buried mounds, seafloor channels, and inter-channel areas. A detailed methodology is developed to
produce a map of angle-invariant (normalized) backscatter data by correcting the local angular backscatter values. The present
paper involves detailed processing steps and related technical aspects of the normalization approach. The presented angle-invariant
backscatter map possesses 12 dB dynamic range in terms of grey scale. A clear distinction is seen between the mound dominated
northern area (Belgica province) and the Gollum channel seafloor at the southern end of the site. Qualitative analyses of
the calculated mean backscatter values i.e., grey scale levels, utilizing angle-invariant backscatter data generally indicate
backscatter values are highest (lighter grey scale) in the mound areas followed by buried mounds. The backscatter values are
lowest in the inter-channel areas (lowest grey scale level). Moderate backscatter values (medium grey level) are observed
from the Gollum and Kings channel data, and significant variability within the channel seafloor provinces. The segmentation
of the channel seafloor provinces are made based on the computed grey scale levels for further analyses based on the angular
backscatter strength. Three major parameters are utilized to classify four different seafloor provinces of the Porcupine Seabight
by employing a semi-empirical method to analyse multibeam angular backscatter data. The predicted backscatter response which
has been computed at 20° is the highest for the mound areas. The coefficient of variation (CV) of the mean backscatter response
is also the highest for the mound areas. Interestingly, the slope value of the buried mound areas are found to be the highest.
However, the channel seafloor of moderate backscatter response presents the lowest slope and CV values. A critical examination
of the inter-channel areas indicates less variability within the estimated three parameters. Financial support of this study
was granted by the European Commission Fifth Framework Project GEOMOUND (contract no. EVK3-CT-1999-00016). 相似文献
10.
Bishwajit Chakraborty Hans Werner Schenke Vijay Kodagali Rick Hagen 《Marine Geodesy》2013,36(1-2):19-26
Utilizing a hull-mounted, multinarrow beam echosounder onboard RV Polarstern, we measured variation of acoustic backscatter with incidence angles at two different sites in the Southern Oceans (Agulhas Plateau and the Riiser Larsen Sea). We modeled the data, using a composite roughness model, including water-sediment interface roughness and sediment volume roughness parameters. The model effectively uses the near normal incidence angle backscatter to determine the seafloor interface roughness parameters employing Helmholtz-Kirchhoff theory. Beyond 20° incidence angles, an application of Rayleigh-Rice theory is made by using a necessary splicing technique (combining both of the theories at 20° incidence angle). The estimated interface and volume roughness parameters are found to be in accordance with the known area geology. 相似文献