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171.
P. P. Nageshwara Rao S. Elango H. R. Rajmohan V. Krishna Murthy 《Journal of the Indian Society of Remote Sensing》2004,32(1):75-79
Photo interpretation and digital classification of IRS LISS -III sensor data have been carried out for a few villages affected
by abnormal health problems in the Kasargod district of Kerala State. Physical location of the affected villages in relation
to the agricultural lands use, watershed characteristics and the extent of cashewnut plantations are studied. It was found
that the villages affected by the health problems are located in the microwatersheds that have steep slopes, nearly circular
in shape, high runoff potential. The first order streams within these micro-watersheds are originating from the cashewnut
plantations that are sprayed with a toxicant called Endosulfan. The study recommends to stop aerial spraying of any toxicant
on the cash crops of these watersheds. 相似文献
172.
In the Dharwar Craton, southern India, gold deposits are found mostly along the six arcuate shear zones passing through late Archaean greenstone belts (2.7 Ga). One such shear zone complex extends for about 400 km within and along the Ramagiri–Hungund schist belt. The Penakacherla sector of this shear zone is excellently exposed, enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration.Metamorphism and deformation under NE–SW compression associated with Archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists. Continued compression generated a 50–100-m-wide shear zone complex consisting of mafic phyllonites. Advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified, K-metasomatic assemblage mainly consisting of chlorite, amphibole, K-mica, plagioclase, ankerite, quartz, Fe-oxides, pyrite, chalcopyrite and arsenopyrite. Networks of quartz and carbonate veinlets, a few millimeters to a few centimeters thick, formed along the foliation planes giving rise to microscopic alteration envelope, in which individual veinlet systems are merged into one another to form a composite alteration system. Gold is found within these quartz veinlets, mafic phyllonites and at their mutual contacts.Hydrothermal fluids have modified the primary major, minor, trace and LREE compositions of host rocks such that their mutual behaviour became non-systematic. Some HFSE and HREE also show minor mobility but the overall REE pattern generally resembles that of the precursor mafic volcanic rocks. Mass and volume loss/gain by Si and Ca has made significant impact on Al, Ti and Zr abundances, which are generally immobile during hydrothermal alteration. However, element pairs such as Zr–Hf, V–Sc and Nb–Ta maintain primary inter-element ratios, although their absolute abundances are drastically diluted. Similarly, ΣREE in highly silicified and carbonatised samples are reduced, but patterns remain similar to those of relatively least altered mafic phyllonites with (LaN/Yb)N between 1 and 3. In some samples, LREE enrichment is observed elevating in (LaN/Yb)N from 3 to 11. Pathfinder elements and base metals such as As, Cd, Cu, Pb, Zn and Sb have been added along with the Au and Ag.δ13C of carbon varies from −16‰ to −21‰ suggesting a biogenic origin, whereas coexisting pyrite δ34S ranges from 1‰ to 3‰, pointing towards the involvement of magmatic or average crustal sulphur. Overall concentrations of K, Rb, Sr, Ba, Nb, Ta, Ti, Cs, Cr, Co, V, Y and Sc and many of the ratios such as K/Rb, La/Sc, La/Yb indicate that metamorphism, devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks. Fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity. 相似文献
173.
M. Thamban S. S. Naik R. Mohan A. Rajakumar N. Basavaiah Witty D’Souza Sarita Kerkar M. M. Subramaniam M. Sudhakar P. C. Pandey 《Journal of Earth System Science》2005,114(5):443-452
Changes in the terrigenous sediment source and transport mechanisms during the late Quaternary have been investigated using
four sediment cores within the Indian sector of Southern Ocean, using the magnetic susceptibility (MS) and sedimentological
records. Sediments deposited during the Holocene and other interglacial periods were characterised by low MS, low sand content,
reduced ice-rafted detritus (IRD) input and increased illite possibly transported via hydrographic advection from the south.
The glacial intervals are characterised by high MS, high sand content, increased IRD input and reduced illite clays, derived
from both local as well as Antarctic sources. Significant reduction in clay fraction and illite content during glacials suggests
that the erosive and transporting capabilities of the deep and bottom waters could have reduced compared to the interglacial
times. The changes in terrigenous influx to this region were significantly influenced by the rhythmic glacial-interglacial
fluctuations in bottom circulation and the position of the Polar Front. 相似文献
174.
Postcolonial geographies of development: Introduction 总被引:1,自引:0,他引:1
175.
A framework for geometric regularization of elevation maps is introduced in this letter. The framework takes into account errors in the data, which form part of standard elevation maps specifications, as well as possible additional user/application-dependent constraints. The algorithm is based on adapting the theory of geometric active surfaces to the problem of regularizing elevation maps. We present the underlying concepts and numerical experiments showing the effectiveness and potential of this theory. 相似文献
176.
Dipnarayan Ganguly Anirban Mukhopadhyay Rahul Krishna Pandey Debasish Mitra 《Journal of the Indian Society of Remote Sensing》2006,34(4):431-435
Study of landforms in Sundarbans deltaic estuary is necessary in regular basis due to its importance and impact on ecology,
climate and economy. Remote sensing has proved as an important tool to study this. Multi-temporal satellite data helps to
delineate the various geomorphic classes in different time domain and also provide inputs to study the coastal erosion and
accretion. Finer spatial and better temporal resolution will be an added adventure for this kind of study. 相似文献
177.
Sanjay Bhatnagar Gopal Krishna & L. Wisotzki 《Monthly notices of the Royal Astronomical Society》1998,299(2):L25-L28
By considering the propagation of low-amplitude magnetohydrodynamic waves in partially ionized plasmas, it is shown that the ion-neutral drift (ambipolar diffusion) induced by the waves can have specific effects on the molecular chemistry of cold material. The chemistry occurring in gas swept by Alfvén waves is described and it is shown that this leads to spatial variations in the deuterium fractionation ratios of, for example, HCO+ and N2 H+ , on spatial scales of a few hundredths of a parsec, depending upon the fractional ionization of the ambient medium. The possibility of detecting interstellar Alfvén waves by molecular spectroscopy and their effect of producing small-scale chemical abundance gradients in molecular clouds are briefly discussed. 相似文献
178.
Y Srinivasa Rao T V Krishna Reddy P T Nayudu 《Journal of the Indian Society of Remote Sensing》1997,25(3):187-194
To evaluate the hydrogeomorphological conditions of Niva river basin Chittoor district, Andhra Pradesh, geological, hydrogeological and geomorphological studies were carried out. through visual interpretation of Landsat 5, FCC with adequate ground truth. The study shows that the Niva river basin is occupied by granites and gneisses of Archaean age with intrusive bodies of dolerites. The recent alluvium deposits are present along the stream courses. The study area is traversed by various directional fractures/lineaments and most of them are NESW, ENE-WSW and EW directions. Groundwater potential of geomorphological units viz. Denudational hill, Residual hill, Pediment, Pediplain and Valley fill is discussed. 相似文献
179.
180.
Geostatistics has traditionally used a probabilistic framework, one in which expected values or ensemble averages are of primary importance. The less familiar deterministic framework views geostatistical problems in terms of spatial integrals. This paper outlines the two frameworks and examines the issue of which spatial continuity measure, the covarianceC (h) or the variogram (h), is appropriate for each framework. AlthoughC (h) and (h) were defined originally in terms of spatial integrals, the convenience of probabilistic notation made the expected value definitions more common. These now classical expected value definitions entail a linear relationship betweenC (h) and (h); the spatial integral definitions do not. In a probabilistic framework, where available sample information is extrapolated to domains other than the one which was sampled, the expected value definitions are appropriate; furthermore, within a probabilistic framework, reasons exist for preferring the variogram to the covariance function. In a deterministic framework, where available sample information is interpolated within the same domain, the spatial integral definitions are appropriate and no reasons are known for preferring the variogram. A case study on a Wiener-Levy process demonstrates differences between the two frameworks and shows that, for most estimation problems, the deterministic viewpoint is more appropriate. Several case studies on real data sets reveal that the sample covariance function reflects the character of spatial continuity better than the sample variogram. From both theoretical and practical considerations, clearly for most geostatistical problems, direct estimation of the covariance is better than the traditional variogram approach.This paper was presented at MGUS 87 Conference, Redwood City, California, 14 April 1987. 相似文献