Terrain characterization using SRTM data   总被引：1，自引：0，他引：1  

P. P. Patel  A. Sarkar 《Journal of the Indian Society of Remote Sensing》2010,38(1):11-24

Earth’s surface possesses relief because the geomorphic processes operate at different rates, and geologic structure plays a dominant role in the evolution of landforms (Thornbury, 1954). The spatial pattern of relief yields the topographic mosaic of a terrain and is normally extracted from the topographical maps which are available at various scales. As cartographic abstractions are scale dependent, topographical maps are rarely good inputs for terrain analysis. Currently, the shuttle radar topography mission (SRTM) provides one of the most complete, highest resolution digital elevation model (DEM) of the Earth. It is an ideal data-set for precise terrain analysis and topographic characterization in terms of the nature of altimetric distribution, relief aspects, patterns of lineaments and surface slope, topographic profiles and their visualisation, correlation between geology and topography, hypsometric attributes and finally, the hierarchy of terrain sub-units. The present paper extracts the above geomorphic features and terrain character of part of the Chotonagpur plateau and the Dulung River basin therein using SRTM data.  相似文献   

Latitudinal trends in morphological characteristics of <Emphasis Type="Italic">Neogloboquadrina pachyderma</Emphasis> (Ehrenberg) along a north–south transect in the south-western Indian Ocean     

Neloy Khare  Pawan Govil  Abhijit Mazumder 《Geo-Marine Letters》2009,29(1):61-69

A total of 25 surficial sediment samples (Peterson grab, gravity and piston cores), collected during the Pilot Expedition to Southern Ocean (PESO) 2004 cruises 199C and 200 onboard the ORV Sagar Kanya along a N–S transect between 9.69°N and 55.01°S, and 80 and 40°E in the Indian Ocean sector of the Southern Ocean (SW Indian Ocean), have been investigated for various morphological features—test size, mean proloculus size and coiling direction (dextral/sinistral forms)—of the planktic indicator species Neogloboquadrina pachyderma (Ehrenberg). The results show that the coiling directions co-vary with temperature and salinity, the abundances of sinistrally coiled forms increasing towards higher latitudes (south of 40°S), whereas dextrally coiled forms show a reverse trend. Similarly, overall test and proloculus sizes depend largely on the physicochemical properties (salinity, temperature, nutrients, calcium saturation) of the ambient water masses. These observations suggest that, particularly at the boundaries between different water masses, variations in morphological features of N. pachyderma can meaningfully be used to reconstruct paleoceanographic conditions from Indian Ocean sediments.  相似文献   

Time-dependent diffusive interactions between dark matter and dark energy in the context of k-essence cosmology     

Abhijit Bandyopadhyay  Anirban Chatterjee 《天文和天体物理学研究(英文版)》2021,(1):15-24

We investigated the scenario of time-dependent diffusive interaction between dark matter and dark energy and showed that such a model can be accommodated within the observations of luminosity distanceredshift data in Supernova la(SN la)observations.We obtain constraints on different relevant parameters of this model from the observational data.We consider a homogeneous scalar field(t)driven by a k-essence Lagrangian of the form L=V(φ)F(X)with constant potential V(φ)=V,to describe the dynamics of dark energy in this model.Using the temporal behaviour of the FRW scale factor,the equation of state and total energy density of the dark fluid,extracted from the analysis of SN la(JLA)data,we have obtained the time-dependence of the k-essence scalar field and also reconstructed the form of the function F(X)in the k-essence Lagrangian.  相似文献   

Validation of IRI-2007 against TEC observations during low solar activity over Indian sector     

N.K. Sethi  R.S. Dabas  S.K. Sarkar 《Journal of Atmospheric and Solar》2011,73(7-8):751-759

Published values of Total Electron Content (TEC) measured by ATS-6 are used to assess the latest available IRI-2007 model during solar minimum over Indian sector covering equatorial to low-mid-latitudes stations. The study reveals that during all seasons and at all locations, in general, the TEC predicted by NeQuick and IRI01-corr options provided in the IRI-2007 model shows much better agreement with the TEC observations as compared to those generated by IRI-2001.option. TEC predicted using NeQuick option found to be little more closer to the observation except at equatorial station during daytime, while IRI-2001 option highly overestimates the TEC in all seasons and times.  相似文献   

Microbial mat structures in profile: The Neoproterozoic Sonia Sandstone,Rajasthan, India     

Pradip Samanta  Soumik Mukhopadhyay  Anudeb Mondal  Subir Sarkar 《Journal of Asian Earth Sciences》2011,40(2):542-549

Ubiquitous microorganisms, especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats. In the absence of grazers and bioturbators, microbial mat is a unique feature of the Proterozoic. Most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding. Nonetheless, bed surface exposures are relatively rare in rock records. This limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed-across sections is needed. The 60 m thick coastal marine interval of the Sonia Sandstone Formation is bounded between two terrestrial intervals, a transgressive lag at the base and an unconformity at the top, and has been chosen for exploration of microbial mat structures in bed-across sections. A wide variety of microbial mat-induced structures in bed-across sections are preserved within the coastal interval of the Sonia Sandstone. Though many of these structures are similar in some aspects with bed surface structures, some of those presented here are new. The palaeogeographic range of these microbial structures extends from supralittoral to neritic. Diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains. SEM and EDAX analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the Sonia Sandstone. Effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous. The mat-cover on sediment surfaces hinders reworking and/or erosion of the sediments thereby increases the net sedimentation rate. Successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these Proterozoic formations could be a target for exploration.  相似文献   

Heavy metal pollution assessment through comparison of different indices in sewage-fed fishery pond sediments at East Kolkata Wetland,India   总被引：3，自引：0，他引：3  

Subhasis Sarkar  Phani Bhusan Ghosh  Alok Kumar Sil  Tapan Saha 《Environmental Earth Sciences》2011,63(5):915-924

The sediments of the raw sewage-fed fishpond system at East Kolkata Wetland (EKW) were analyzed for heavy metal content in a comprehensive way. Various indices of contamination like enrichment factor (EF), geo-chemical index (I _geo), modified degree of contamination (mD_C), and pollution load index (PLI) were assessed. In all cases, instead of literature values, the metal concentrations of less contaminated sites, separated by the statistical approach of the hierarchical cluster analysis, were used as baseline values. In the present study, about 70% of the pond sediments are found uncontaminated, 5% display low degree of contamination and 25% are designated as moderate degree of contamination. Both the EF and I _geo indices highlighted that the metals lead (Pb), cadmium (Cd), and chromium (Cr) are responsible for the contamination while there is little anthropogenic input in cases of Cu, Zn, and Ni. Most of the ponds situated near the main sewage flowing canals as well as the main traffic highway and close to the solid waste dumping areas recorded higher degree of metal contamination as evident from spatial variation of mD_C and PLI indices in the study area. Indices comparison study clearly indicates that although these are calculated using different methods, these may or may not produce the same indices values and hence the values should neither be compared nor be averaged. But all the above indices are directly related to a common term contamination factor (CF). Classification of contamination levels based on these CF values is found to be similar and this classification is only valid up to the level of high degree of contamination. Thus, the use of any one of these indices is sufficient to classify the degree of contamination of an area. However, to evaluate the contamination per metal, both I _geo and EF are effective while, to assess the composite effect of all the metals, PLI is preferable to mD_C.  相似文献   

Ecological consideration of trace element contamination in sediment cores from Sundarban wetland,India   总被引：2，自引：1，他引：1  

E. V. Silva Filho  M. P. Jonathan  M. Chatterjee  S. K. Sarkar  S. M. Sella  A. Bhattacharya  K. K. Satpathy 《Environmental Earth Sciences》2011,63(6):1213-1225

This article reports on the concentration of selected trace elements (Mn, Zn, Cr, Cu, Ba, As, B, V, and Hg) and major elements (Fe and Al) from the intertidal sediment cores from Sundarban wetland, India. This is a typical meso-macrotidal estuarine area affected by domestic and industrial activities located upstream. The overall concentrations range is low to moderate, indicating the environmental conditions in the outfall zone (grain size, hydrodynamic regime, and confinement), which favors the in situ accumulation of pollutants. The extent of contamination from trace elements in Sundarban core sediments is evaluated through a two-pronged approach: (i) by determining the metal enrichment in the sediments through the calculation of Pollution Load Index (PLI), Enrichment Factor (EF) and Index of Geoaccumulation (I _geo), and (ii) by defining a potential level of biological risk by the use of quality criteria such as Threshold Effect Level (TEL) and Effects Range-Low (ERL) benchmarks. On the basis of the calculated indices, sediments are particularly enriched with Cr, Cu, B, V, and As. Those enrichments seem to be due to the fine granulometry of the regions with Fe and Mn oxi-hydroxides being the main metal carriers. Trace Elements input to the Sundarban wetland need to be kept under strict control in future specially with reference to As since, according to TEL and ERL benchmarks, it already appears to be associated with a potential biological risk.  相似文献   

Experimental investigation of gas-water relative permeability for gas-hydrate-bearing sediments from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope   总被引：1，自引：0，他引：1  

Andrew JohnsonShirish Patil  Abhijit Dandekar 《Marine and Petroleum Geology》2011,28(2):419-426

Permeability of hydrate reservoirs found in nature is likely to be heavily influenced by the percent of the pore volume occupied by hydrates. The quantification of how hydrate saturation affects permeability is of key interest for reservoir engineering studies. In this study, an experimental setup was modified to test permeability characteristics of unconsolidated core samples containing various saturations of methane hydrates. Hydrates were formed in the unconsolidated samples using a refrigerated core holder connected to a brine and methane injection system. Studies of this type conducted to date have rarely been performed on core samples recovered from actual hydrate-bearing sedimentary sections from natural hydrate intervals. Samples from the Mount Elbert site on the Alaska North Slope (ANS) were used for this study.Relative permeability measurements using hydrate constituent components (e.g. water and methane) are not very desirable due to difficulties in preventing additional hydrate formation during displacement experiments. Relative permeability measurements performed with hydrate constituent components (e.g. water and nitrogen) can help to significantly mitigate issues with additional hydrate formation. However, unsteady state relative permeability experiments produce piston like displacement results suggesting that steady state experiments might be preferable.It was observed that as in previous work using consolidated core samples, permeability of both brine and gases was reduced in unconsolidated hydrate-bearing core samples. Experimental results show that low to moderate hydrate saturations (1.5 to 36%) can significantly reduce permeability of porous media. These saturations, in fact, are lower than hydrate saturations observed in the natural hydrate systems at Mount Elbert.  相似文献   

Incipient Charnockite Formation in Leptynite from Vizianagaram, Andhra Pradesh: Implication for Pan-African (?) Crustal Reworking in the Eastern Ghats Belt     

Niloy Ranjan Datta  P. Sengupta  Aparajita Gangopadhyay  Sushmita Sarkar 《Gondwana Research》2001,4(4):603-604

  相似文献   

Tectonic Significance of Fissure Veins Associated with Pseudotachylites of the Kui-Chitraseni Shear Zone, Aravalli Mountain, NW India     

Sunayana Sarkar  T.K. Biswal   《Gondwana Research》2005,8(2):277-282

Kui-Chitraseni Shear Zone of the Precambrian Aravalli Mountain, NW India is marked by a nearly 400 m-wide NE-SW trending belt of cataclasites developed on the granites and metasediments of the Delhi Supergroup. The cataclasites are criss crossed by pseudotachylite and fissure-veins. While the pseudotachylites are aphanitic to microlitic, the fissure veins are characterized by syntaxial-bitaxial as well as unitaxial growth of elongate quartz grains. Textural study of the fissure veins suggests crystallization of quartz grains in a dilational environment in hydrous condition. Contrarily the pseudotachylites bear the evidence of frictional melting of rocks under anhydrous conditions. Since in many instances it is observed that the fissure veins have replaced the pseudotachylites following the crack seal mechanism, the formation of fissure veins is considered to be latekinematic to pseudotachylites. Hence it is interpreted that the pseudotachylites and fissure veins were formed in two distinct tectonic events. While pseudotachylites were formed in a compressional setting resulted from thrusting along the shear zone, the fissure veins have been formed in an extensional setting during a late stage normal faulting. In light of this tectonic rejuvenation along the Kui-Chitraseni Shear Zone, various lineaments present within the Aravalli Mountains need further study for understanding the evolution of the region.  相似文献