Image analysis of seafloor photographs for estimation of deep-sea minerals     

Rahul Sharma  S. Jai Sankar  Sudeshna Samanta  A. A. Sardar  D. Gracious 《Geo-Marine Letters》2010,30(6):617-626

Factors such as non-uniform illumination of seafloor photographs and partial burial of polymetallic nodules and crusts under sediments have prevented the development of a fully automatic system for evaluating the distribution characteristics of these minerals, necessitating the involvement of a user input. A method has been developed whereby spectral signatures of different features are identified using a software ‘trained’ by a user, and the images are digitized for coverage estimation of nodules and crusts. Analysis of >20,000 seafloor photographs was carried out along five camera transects covering a total distance of 450 km at 5,100–5,300 m water depth in the Central Indian Ocean. The good positive correlation (R² > 0.98) recorded between visual and computed estimates shows that both methods of estimation are highly reliable. The digitally computed estimates were ∼10% higher than the visual estimates of the same photographs; the latter have a conservative operator error, implying that computed estimates would more accurately predict a relatively high resource potential. The fact that nodules were present in grab samples from some locations where photographs had nil nodule coverage emphasises that nodules may not always be exposed on the seafloor and that buried nodules will also have to be accounted for during resource evaluation. When coupled with accurate positioning/depth data and grab sampling, photographic estimates can provide detailed information on the spatial distribution of mineral deposits, the associated substrates, and the topographic features that control their occurrences. Such information is critical for resource modelling, the selection of mine sites, the designing of mining systems and the planning of mining operations.  相似文献   

Metamorphic evolution of the Naga Hills eclogite and blueschist, Northeast India: implications for early subduction of the Indian plate under the Burma microplate     

N. CHATTERJEE  N. C. GHOSE 《Journal of Metamorphic Geology》2010,28(2):209-225

Tectonic slices and lenses of eclogite within mafic and ultramafic rocks of the Early Cretaceous–Eocene Naga Hills ophiolite were studied to constrain the physical conditions of eastward subduction of the Indian plate under the Burma microplate and convergence rate prior to the India–Eurasia collision. Some of the lenses are composed of eclogite, garnet-blueschist, glaucophanite and greenschist from core to margin, representing a retrograde hydrothermal alteration sequence. Barroisite, garnet, omphacite and epidote with minor chlorite, phengite, rutile and quartz constitute the peak metamorphic assemblage. In eclogite and garnet-blueschist, garnet shows an increase in Mg and Fe and decrease in Mn from core to rim. In chlorite in eclogite, Mg increases from core to rim. Inclusions of epidote, glaucophane, omphacite and quartz in garnet represent the pre-peak assemblage. Glaucophane also occurs profusely at the rims of barroisite. The matrix glaucophane and epidote represent the post-peak assemblage. The Fe³⁺ content of garnet-hosted omphacite is higher than that of matrix omphacite, and Fe³⁺ increases from core to rim in matrix glaucophane. Albite occurs in late stage veins. P – T pseudosection analysis indicates that the Naga Hills eclogites followed a clockwise P – T path with prograde metamorphism beginning at ∼1.3 GPa/525 °C and peaking at 1.7–2.0 GPa/580–610 °C, and subsequent retrogression to ∼1.1 GPa/540 °C. A comparison of these P – T conditions with numerical thermal models of plate subduction indicates that the Naga Hills eclogites probably formed near the top of the subducting crust with convergence rates of ∼ 55–100 km Myr⁻¹, consistent with high pre-collision convergence rates between India and Eurasia.  相似文献   

Hybrid Gaussian-cubic radial basis functions for scattered data interpolation     

Pankaj K. Mishra  Sankar K. Nath  Mrinal K. Sen  Gregory E. Fasshauer 《Computational Geosciences》2018,22(5):1203-1218

Scattered data interpolation schemes using kriging and radial basis functions (RBFs) have the advantage of being meshless and dimensional independent; however, for the datasets having insufficient observations, RBFs have the advantage over geostatistical methods as the latter requires variogram study and statistical expertise. Moreover, RBFs can be used for scattered data interpolation with very good convergence, which makes them desirable for shape function interpolation in meshless methods for numerical solution of partial differential equations. For interpolation of large datasets, however, RBFs in their usual form, lead to solving an ill-conditioned system of equations, for which, a small error in the data can cause a significantly large error in the interpolated solution. In order to reduce this limitation, we propose a hybrid kernel by using the conventional Gaussian and a shape parameter independent cubic kernel. Global particle swarm optimization method has been used to analyze the optimal values of the shape parameter as well as the weight coefficients controlling the Gaussian and the cubic part in the hybridization. Through a series of numerical tests, we demonstrate that such hybridization stabilizes the interpolation scheme by yielding a far superior implementation compared to those obtained by using only the Gaussian or cubic kernels. The proposed kernel maintains the accuracy and stability at small shape parameter as well as relatively large degrees of freedom, which exhibit its potential for scattered data interpolation and intrigues its application in global as well as local meshless methods for numerical solution of PDEs.  相似文献   

Assessment of nitrate contamination of Lidder catchment Kashmir, India   总被引：1，自引：1，他引：0  

Imran A. Dar  K. Sankar  Tanzeem S. Shah  Mithas A. Dar 《Arabian Journal of Geosciences》2012,5(2):233-243

Nitrate contamination in the groundwater from various sources is one of the major problems of water resources in Liddercatchment, Kashmir. Systematic sampling was carried out during summer 2007, with a view to understand the source of nitrate ions in the groundwater of the Lidder catchment. Twelve sample sites were selected and samples were taken for a baseline study to understand the geochemistry of the groundwater and to assess the overall physico-chemical characteristics. Results showed that NO ₃ ^? concentration in ranged from 18.72?mg/L to 75.93?mg/L with an average of 47.03?mg/L. More than 80% (83.33%) of the samples collected from various sampling stations had nitrate concentrations exceeding the threshold value of 20?mg/L, and 58.33% of the samples collected had nitrate concentrations higher than 50?mg/L, the maximum acceptable nitrate concentration for drinking water. There is a wide spatial variation in the nitrate concentration in the groundwater. Monitoring the water quality of various sampling stations showed that the lowest concentrations of nitrate were found in the wet season (January, February, and December), while the highest concentrations were found in the dry season (August, September). Numerous human perturbations have been detected affecting the water quality of Lidder catchment. Disposal of sewage and animal wastes was found to contribute about 85% of total nitrate pollution in the study area. Based on the trend analysis (using previous data), future scenario of nitrate pollution has been predicted in the study area. The results of this study are useful to highlight one of the most important environmental problems, namely the degradation of the water quality, and may serve to alert and encourage local and national authorities to take substantial steps and actions to protect and manage water quality.  相似文献   

Effect of quarrying on the slope stability in Banasuramala: an offshoot valley of Western Ghats,Kerala, India     

K. S. Sajinkumar  G. Sankar  V. R. Rani  P. Sundarajan 《Environmental Earth Sciences》2014,72(7):2333-2344

The Narippara area, which is nestled in the Banasuramala of Wayanad district, witnessed initiation of landslide, which was manifested in the form of curvilinear cracks running for a length of 170 m. In the event of continuous rainfall, these cracks may get reactivated, leading to a major landslide. This could affect the life and livelihood of a large number of families living downslope and could cause extensive damage to property. Extensive mining for building stones in this area has been a cause for much concern amongst the local population. This study aims at understanding the impact of quarrying on slope stability through geotechnical, geophysical and environmental impact assessment (EIA). Geotechnical analysis shows that the area is stable under dry condition but parts of the area are critical under wet and saturated conditions. Moreover, resistivity studies revealed that the cracks that had developed extend up to the bedrock and the suspected mechanism of failure will be translational in nature. EIA reveal that due to quarrying and mining operations, the possibility of land disturbances cannot be ruled out during the monsoon season. In the present study, an attempt is also made to suggest management strategies for mitigating further effects of landslides in this area.  相似文献   

Assessing the feasibility of CO<Subscript>2</Subscript>-enhanced oil recovery and storage in mature oil field: A case study from Cambay basin     

Shib Sankar Ganguli  Nimisha Vedanti  Idar Akervoll  V. P. Dimri 《Journal of the Geological Society of India》2016,88(3):273-280

The utilization of anthropogenic CO₂ for enhanced oil recovery (EOR) can significantly extend the production life of an oil field, and help in the reduction of atmospheric emission of anthropogenic CO₂ if sequestration is considered. This work summarizes the prospect of EOR and sequestration using CO₂ flooding from an Indian mature oil field at Cambay basin through numerical modelling, simulation and pressure study based on limited data provided by the operator. To get an insight into CO₂-EOR and safe storage process in this oil field, a conceptual sector model is developed and screening standard is proposed keeping in mind the major pay zone of the producing reservoir. To construct the geomodel, depth maps, well positions and coordinates, well data and well logs, perforation depths and distribution of petrophysical properties as well as fluid properties provided by the operator, has been considered. Based on the results from the present study, we identified that the reservoir has the potential for safe and economic geological sequestration of 15.04×10⁶ metric ton CO₂ in conjunction with a substantial increase in oil recovery of 10.4% of original oil in place. CO₂-EOR and storage in this mature field has a bright application prospect since the findings of the present work could be a better input to manage the reservoir productivity, and the pressure field for significant enhancement of oil recovery followed by safe storage.  相似文献   

Studies on flow characteristics of coal–oil–water slurry system     

Subrata Kumar Majumder  Kamal ChandnaDhiren Sankar De  Gautam Kundu 《International Journal of Mineral Processing》2006

Experiments were carried out to investigate the rheological properties of coal–oil–water suspension containing solids of different sizes. Two different coal samples with mean particle sizes of 120 mesh, 175 mesh and 220 mesh were used. The coal concentration was varied from 5% to 25% by weight. Sodium silicate has been used as an additive to study the behavior of the variation of average viscosity of the suspension. A generalized correlation has been developed to predict the average viscosity of suspension in terms of particle diameter of the coal, concentration of coal, viscosity of the suspending medium and the concentration of water. Experimental investigations revealed that coal–oil–water suspensions show an increase in the viscosity with decrease in coal size but with the addition of an additive, the average viscosity tends to decrease initially up to a certain optimum dosages and thereafter it increases with further addition of additives. Two empirical correlations are proposed for average viscosity of the coal–oil–water suspension, μ_sL in terms of physical properties of the solid and viscosity of the suspending medium with and without additives.  相似文献   

Characterization of magnetite particles in shocked quartz by means of electron- and magnetic force microscopy: Vredefort, South Africa     

Marthinus Cloete  Rodger J. Hart  Herbert K. Schmid  Martyn Drury  Chris M. Demanet  K. Vijaya Sankar 《Contributions to Mineralogy and Petrology》1999,137(3):232-245

Submicroscopic opaque particles from highly shocked granite-gneisses close to the core of the Vredefort impact structure have been investigated by means of micro-analytical techniques with high spatial resolution such as electron diffraction, orientation contrast imagery and magnetic force microscopy. The opaque particles have been identified as nano- to micro-sized magnetite that occur in several distinct modes. In one sample magnetite occurs along relict planar deformation features (PDFs) in quartz, generally accepted as typical shock lamellae. The magnetite particles along shock lamellae in quartz grains virtually all show uniform crystallographic orientations. In most instances, the groups of magnetite within different quartz grains are systematically misorientated such that they share a subparallel <101> direction. The magnetite groups of all measured quartz grains thus appear to have a crystallographic preferred orientation in space. In a second sample, orientations of magnetite particles have been measured in microfractures (non-diagnostic of shock) of quartz, albite and in the alteration halos, (e.g. biotite grains breaking down to chlorite). The crystallographic orientations of magnetite particles are diverse, with only a minor portion having a preferred orientation. Scanning electron microscopy shows that magnetite along the relict PDFs is invariably associated with other microcrystalline phases such as quartz, K-feldspar and biotite. Petrographic observations suggest that these microcrystalline phases crystallized from locally formed micro-melts that intruded zones of weakness such as microfractures and PDFs shortly after the shock event. The extremely narrow widths of the PDFs suggest that heat may have dissipated rapidly resulting in melts crystallizing relatively close to where they were generated. Magnetic force microscopy confirms the presence of magnetic particles along PDFs. The smallest particles, <5 μm with high aspect ratios 15:1 usually exhibit intense, uniform magnetic signals characteristic of single-domain magnetite. Consistent offsets between attractive and repulsive magnetic signals of individual single-domain particles suggest consistent directions of magnetization for a large proportion of particles. Received: 16 November 1998 / Accepted: 17 May 1999  相似文献   

Trace element characteristics,REE patterns and partition coefficients of zircons from different geological environments—A case study on Indian zircons   总被引：1，自引：0，他引：1  

A.V. Murali  R. Parthasarathy  T.M. Mahadevan  M.Sankar Das 《Geochimica et cosmochimica acta》1983,47(11):2047-2052

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On the vibrations of a composite orthotropic cylinder placed in a magnetic field     

Hari Sankar Chakraborty 《Pure and Applied Geophysics》1969,76(1):71-78

Summary The problems of radial vibration of a composite orthotropic cylinder subjected to a uniform axial magnetic field forms the chief interest of the paper.  相似文献