排序方式： 共有15条查询结果，搜索用时 31 毫秒
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.
Sumanta Dandapath Andrew Menezes Bishwajit Chakraborty John Kurian Koppella N. Prudhvi Raju 《Marine Geodesy》2018,41(2):177-200
An assessment of the multibeam sonar data of the central Western Continental Margins of India has been carried out to evaluate the seafloor geomorphology and processes by examining the geomorphological attributes e.g., slope, sediments, structures, etc. associated with geomorphic features. The variation in relief and the features located in the region have been mapped and interpreted collectively by utilizing several geospatial mapping tools. The backscatter strength across the area, apparently congruent with the local relief, has helped to examine the sediment movement on the seafloor. The prominent features found in the region include faults, pockmarks, mounds, submarine terraces, and submerged fossil reefs. Several areas with varying topography engender comparable fractal dimension at short scale breaks, and the probability density functions (PDFs) utilizing backscatter data depicting overlapping classes. The present study highlights how fractals and scale break parameters can be utilized to determine the seafloor processes and associated sedimentological dynamics in a complex geographical environment with strong bottom currents, seasonal upwelling, and faulted structure. The role and impact of the various geomorphic processes on the reworking of sediment movement and the overall progression of the seafloor morphology has been revealed for the first time in this part of the ocean bottom. 相似文献
3.
Sumanta Dandapath Bishwajit Chakraborty Nicolas Maslov Siddaiah M. Karisiddaiah Dhrupad Ghosh William Fernandes Andrew Menezes 《Marine and Petroleum Geology》2012,29(1):115-128
Here we apply quantitative technique to describe the seafloor seepages based on the multi-beam backscatter and bathymetric investigations to characterize the pockmark morphology. The variable seafloor backscatter strength for coarser seafloor sediments are related to the diagenesis derived from biodegraded seepages. In this regard, box counting method is used to estimate ‘fractal dimension’ for backscatter imagery data of 398 blocks. These blocks are further sub-grouped into six classes depending on the spread of pockmark related seepages. The study area lies 102 km west off Marmagao along the central west coast of India which contains pre-dominantly (70%) gas-charged sediments. Comparison between the estimated self-similar fractals reveals that there is approximately 97% correlation between the box (Dbox) and information (Dinfo) dimensions. Box dimension–derived fractal dimension values, suggest that the seepages are more along the fault trace in deeper waters, in comparison to sparsely distributed shallow water seepages. Besides, this poor seepage is confined within the smooth to moderately rough seafloor. It is established that the high backscatter strength along the upper slope of the pockmark region having higher fractal dimensions reflects multifractal behavior of seepage distribution. Entire area indicates patchy seepage patterns as supported by estimated fractal values showing intermittent fluctuations, which emphasizes non-linear behavior. Estimated self organizing criticality (SOC) parameters for six representative blocks reveal that the nature of pockmark, fault trace, sediment nature coupled with slumping of pockmark’s wall, sediment movement due to bottom currents are controlling the dynamic balance in the area seepage system. Further, our study emphasizing the multifractal behavior of seepage blocks, clearly depicts the drift in the seepage pattern. 相似文献
4.
5.
Selection of a set of dominant echo features to classify seafloor sediments using a multilayer perceptron neural network is
investigated at two acoustic frequencies (33 and 210 kHz). Several sets of inputs with different combinations of two, three,
four, five, and six echo features are exploited with three-layer neural networks. The performances of the networks are analyzed
to assess the most discriminating set of echo features for classification of seafloor sediments. The results of the overall
average performances reveal that backscatter strength and time spread are the two most important echo features at 33 kHz,
whereas backscatter strength has higher discriminating characteristics at 210 kHz for seafloor sediment classification. In
addition, a set of four echo features consisting of backscatter strength, time-spread, statistical skewness, and Hausdroff
dimension gives the highest success at both the acoustic frequencies. 相似文献
6.
Application of quantitative angular backscatter modelling to manganese nodule-bearing areas of the Central Indian Ocean Basin (CIOB) has been initiated at NIO during the year 1998. Studies were aimed to establish the suitability of seafloor backscattering in delineating seafloor parameters characteristic of nodule-rich sediments. In this paper, processed Hydrosweep multi-beam backscatter data from 45 spot locations in the CIOB (where nodule samples are available) were analysed to estimate seafloor and sediment volume roughness parameters. The application of a composite roughness model to a nodule-bearing region (6,600 km2) of the CIOB, to determine seafloor interface roughness parameters from a multi-beam backscatter dataset, shows only four power law sets. The results attest 80% of the nodule-bearing seafloor to be smooth in terms of interface roughness parameters at micro-topographic level. The sediment volume roughness parameters are dominant only in 29% of the smooth interface roughness sites. This indicates that 51% of the seafloor area possesses negligible (interface and volume) roughness. A critical analysis using pseudo-side-scan records from 12 selected locations in the study area affirms the combined importance of the seafloor interface and sediment volume roughness parameters for precise determination of manganese nodule abundance. 相似文献
7.
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
8.
Morphology of pockmarks along the western continental margin of India: Employing multibeam bathymetry and backscatter data 总被引：1，自引：0，他引：1
Sumanta Dandapath Bishwajit Chakraborty Siddaiah M. Karisiddaiah Andrew Menezes Govind Ranade William Fernandes Davidas K. Naik K.N. Prudhvi Raju 《Marine and Petroleum Geology》2010
This study addresses the morphology of pockmarks along the western continental margin of India using multibeam bathymetry and backscatter data. Here, for the first time we have utilized the application of ArcGIS (Geographical Information System) for understanding the morphology of pockmarks from the western continental margin of India. The pockmarks observed in water depths of 145–330 m are circular, elliptical or elongated in plan-view, with an average length and width of 157 (±72) m and 83 (±19) m respectively. The average pockmark relief and perimeter are 1.9 (±0.9) m and 412 (±181) m, respectively. The pockmarks have average areas and volumes of 10 759 m2 and 15 315 m3 respectively. Spatial separation that coincides with 210 m isobath divides the pockmarks into two groups with differing distributions and morphologies. These pockmarks originated from seepages of biogenic or thermogenic gas or from pore fluids from deeper sources, migrated vertically along the faults. Besides a possible structural control, the pockmark morphologies are also affected by bottom currents and/or by submarine slumping. The average acoustic backscatter strength from pockmark centre is higher (−35 dB) than the average backscatter of the total area (−40 dB), which suggests their possible linkage to the precipitation of diagenitic minerals from biodegradation of seepage material. 相似文献
9.
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
10.
A study is conducted to estimate the accurate attitude of a ship's motion and the estimation is used to arrive at the corrections required for a farfield pattern of a coaxial circular array. The relevant analytical expression is developed for the computation of moving average filter weights to estimate the ship's attitude for beamsteerings at different sea conditions. Farfield patterns are presented for different steered directions for the coaxial circular array of the additive type, and the multiplicative array technique is also used for beamsteering for higher steering angles to observe its control on the sidelobes as well as for the main beamwidths. In order to introduce an adaptive filter to estimate the accurate attitude for stable sonar platform, an adaptive parameter is examined for bathymetric applications where nonstationary ship movement prevails. 相似文献