Geochemistry of aerosols of northwestern part of India adjoining the Thar desert     

Sudesh Yadav 《Geochimica et cosmochimica acta》2004,68(9):1975-1988

The northwestern part of India, which includes the Thar desert on its western side, is a hot and arid region with intense aeolian activity and transport of aerosols by the prevailing SW-W summer winds. Different size fractions of aerosols (free fall = FF, suspended particulate matter = SPM, PM₁₀ = <10 μm, and >10 μm) from air were sampled simultaneously at four locations along the dominant wind trajectory for ∼600 km. These aerosols and deposited surface sediments were characterized for their texture, mineralogy and geochemistry including REE and Sr isotopes. Within each size fraction, a bimodal distribution of grain size was observed. Quartz is the dominant mineral followed by K-feldspar, mica, calcite, chlorite and plagioclase. Garnet, amphibole, titanite and zircon are some of the identified heavy minerals. All samples, particularly those collected during summer, are compositionally homogeneous, including in their REE geochemistry, and are similar to average upper continental crust (UCC). However, in the winter aerosol samples, large deviations from the UCC composition are observed. This is attributed to meteorological parameters such as low wind velocity and temperature inversions in the winter season. During winter, secondary non-silicate and anthropogenic materials become important sources to Ca, Na, Mg, K, Ba and Ni budget; also reduction in the uptake and transport of heavy minerals lowered the concentration of Ti, Zr, Y, Cr, and REE in the aerosols. Geochemical coherence among aerosols, deposited surface sediments and the Thar sands, and the limited Sr isotopic data indicate that the Thar sediments and certain lithotectonic units of the Himalayan orogen are the proximal and distal crustal sources, respectively, for the aerosols in this region. Prevailing aridity and strong summer winds, and the presence of river alluvium in the Thar act together to transport silt rich dust, the removal of which could be a possible mechanism of ongoing desertification.  相似文献   

Crop classification accuracy as influenced by training strategy,data transformation and spatial resolution of data     

T T Medhavy  Tara Sharma  R P Dubey  R S Hooda  K E Mothikumar  M Yadav  M L Manchanda  D S Ruhal  A P Khera  S D Jarwal 《Journal of the Indian Society of Remote Sensing》1993,21(1):21-28

The possibility of improving classification accuracies using different training strategies and data transformations within the framework of a supervised maximum likelihood classification scheme was explored in this study. The effect of spatial resolution of data on the accuracy of classification was also studied Single-pixel training strategy resulted in improved classification accuracy over the block-training method. Data transformations gave no significant improvements in accuracy over untransformed data. There was a reduction in classification accuracy as resolution of data improved from 72 m (LISS I) to 36 m (LISS II) while other sensor characteristics remained same.  相似文献   

Pole-dipole resistivity sounding technique for shallow investigations in hard rock areas     

G. S. Yadav 《Pure and Applied Geophysics》1988,127(1):63-71

Theory of the pole-dipole resistivity sounding technique and its application in the hard rock areas for shallow groundwater exploration is presented in this paper. The different components of electric field produced by the point source of current, situated over the ground surface, are measured by a dipole placed at a large distance from the source. The theory of the method is rather simple, suggesting two configurations, namely radial pole-dipole and axial pole-dipole. Theoretical expressions derived for the apparent resistivity over layered Earth are directly related to the Schlumberger apparent resistivity, whereas expressions for geometrical factor for pole-dipole and Schlumberger configuration are different. The proposed technique has been tested in actual field conditions having different rock types. A few examples are presented along with Schlumberger sounding curves which confirm the applicability of the proposed sounding technique.  相似文献   

Focal-mechanism solutions of earthquakes and tectonics of the hindukush region   总被引：1，自引：0，他引：1  

Avadh Ram  Lalaji Yadav 《Tectonophysics》1984,104(1-2)

Seventeen focal-mechanism solutions have been obtained for earthquakes occurring in the Hindukush region using P-wave first motion directions observed from short as well as long period records. These solutions have indicated a thrust type of faulting. Some of the solutions show small components of strike slip motions. The trend of nodal planes in these solutions was found to vary between northeast and southeast directions. The dip of the compressional axes rarely exceeds 25°. Orientation of tensional axes was found to be almost vertical in all cases. These findings together with the spatial distribution of earthquakes in the Hindukush region suggested that earthquakes were caused by down-dip extension within a sinking slab.  相似文献   

Tree-ring-based hydrological records for western Himalaya, India, since a.d. 1560     

Jayendra Singh  Won-Kyu Park  Ram R Yadav 《Climate Dynamics》2006,26(2-3):295-303

We analysed 565 increment cores from 325 Himalayan cedar [Cedrus deodara (Roxb.) G. Don] trees growing at 13 moisture-stressed, widely distributed sites in the western Himalayan region. We found a strong positive relationship between our tree-ring width chronologies and spring precipitation which enabled us to reconstruct precipitation back to a.d. 1560. This reconstruction is so far the longest in this region. The calibration model explains 40% variance in the instrumental data (1953–1997). The most striking feature of the reconstruction is the unprecedented increase in precipitation during the late twentieth century relative to the past 438 years. Both wet and dry springs occurred during the Little Ice Age. A 10-year running mean showed that the driest period occurred in the seventeenth century while the wettest period occurred in the twentieth century. Spectral analysis of the reconstructed series indicated a dominant 2-year periodicity.  相似文献   

Probabilistic assessment of earthquake hazard in the Andaman–Nicobar–Sumatra region     

Mishra  Minakshi  Abhishek  Yadav  R. B. S.  Sandhu  Manisha 《Natural Hazards》2021,105(1):313-338

Natural Hazards - The Andaman–Nicobar–Sumatra (ANS) region is a very hazardous area on the globe, which has witnessed a megathrust earthquake of Mw 9.2 on 26 December 2004 and several...  相似文献   

Rural Road Surface Extraction Using Mobile LiDAR Point Cloud Data     

Manohar Yadav  Ajai Kumar Singh 《Journal of the Indian Society of Remote Sensing》2018,46(4):531-538

The existing roadway infrastructures are mostly archived with two-dimensional (2D) drawings that lack the possibility for three-dimensional (3D) interpretation and advanced 3D analysis. The mobile LiDAR system (MLS) is gaining popularity in 3D mapping applications along various types of road corridors. MLS achieves the highest data quality and completeness among the traditional roadway data collection methods. The rural roads in different countries especially in India form a substantial portion of the road network. Therefore the proper maintenance and road safety analysis of rural roads are recommended activity, which could be addressed using detailed 3D road surface information. The absence of raised curb at road boundary, and presence of complexity, heterogeneity and occlusions along the rural roadway settings restrict the use of existing studies for road surface extraction using MLS point cloud data. Therefore considering the above requirement, this research paper proposes a two-stage method. The first stage extract planar ground surfaces which are further used to filter road surface in the second stage. Global properties of road, that is, topology and smoothness and its radiometric response to laser beam of MLS are used in the second stage. MLS point cloud data of rural roadway were used to test the proposed method. The road surface points were accurately extracted without being affected by the absence of raised curb and hanging objects over the road surface, that is, tree canopies and overhead power lines. The quantitative assessment of the proposed method was performed in terms of correctness, completeness and quality, which were 96.3, 94.2, and 90.9%, respectively.  相似文献   

Contamination Assessment and Site-Management Tool (CAST): A Browser-Based Tool for Site Assessment     

Prabhas K. Yadav  Sandhya Birla  Vedaanti Baliga  Rudolf Liedl  B. R. Chahar  Charles J. Werth 《Ground water》2022,60(2):275-283

Groundwater dependency is increasing globally, while millions of potentially contaminated sites are yet to be characterized for contamination levels. In particular, groundwater contamination due to light nonaqueous phase liquids (LNAPLs) continues to be a global challenge. Mathematical approaches (i.e., analytical, semi-analytical, empirical, numerical) are preferred for an initial site assessment to circumvent the high characterization costs and limited site data availability. However, the site-specific nature of contamination restricts the generalization of any single approach. Hence, the requirement is for an easy-to-use computing interface that provides site-specific data management, the selection and use of multiple-model interfaces for computing, and site characterization, with extension for the latest models as they become available. This work provides one such interface called CAST or Contamination Assessment and Site-management Tool. CAST is an open-source browser-based (online/offline) tool that provides an interface for six different analytical models (e.g., BIOSCREEN-AT), a MODFLOW based numerical model, and two empirical models (including a hybrid numerical-analytical model). Additionally, CAST includes interfaces for site data management, their evaluation, and scenario-based modeling. CAST's development is in a modular format, which simplifies the addition of new computing or data interfaces. Furthermore, the entire code-base of CAST is based on open-source (dominantly Python programming) libraries and standards. This further simplifies the modification or extension of this tool. This paper introduces CAST, its different computing, and data management interfaces and provides examples of the tool's functionality primarily for the initial evaluation of contaminated sites.  相似文献   

Petrology and isotopic evolution of granulites from central Madurai Block (southern India): reference to Ediacaran crustal evolution     

S. Tewari  M. K. Yadav  R. Yadav 《International Geology Review》2018,60(15):1792-1815

The Madurai Block, constituting part of the southern granulite terrain in southern India, has contributed significantly towards understanding the UHT (ultrahigh-temperature) granulites that serve as a window into the mid-lower continental crust. The dominant rock types are charnockites, sapphirine-bearing granulites, garnet cordierite gneisses, and quartzites. Significant textural relations reveal multiphase reactions responsible for the formation of diverse mineral parageneses during prolonged metamorphic history of the area. Prograde reaction is evident from the textural relationship where biotite/sillimanite relics are seen as inclusion in garnet/orthopyroxene, suggesting dehydration reactions. The symplectitic assemblages that formed during isothermal decompression involve a series of cordierite-forming reactions, followed by retrogression and cooling. Variety of mineral assemblages present in the rocks of this area offer a wide spectrum of P–T sensors that provide details on the physical conditions of metamorphism. For the rigorous interpretation of the P–T path in the Perumalmalai area, quantitative phase diagrams (P–T pseudosections) have been constructed and contoured for the compositional as well as modal isopleths of involved mineral phases. The rocks of Perumalmalai area document a clockwise decompression P–T trajectory, consistent with crustal thickening followed by extensional collapse. SHRIMP U–Pb ages from zircon associated with sapphirine-bearing granulite facies rocks of Perumalmalai area suggest a widespread Ediacaran tectonothermal event. The occurrence of Ediacaran UHT metamorphism followed by isothermal decompression in the Madurai Block is consistent with the timing and physical conditions associated with the formation of East African Orogen during the amalgamation of Gondwana.  相似文献   

Potential role of kinetic Alfvén waves and whistler waves in solar wind plasmas     

P. Nandal  N. Yadav  R. P. Sharma  M. L. Goldstein 《Astrophysics and Space Science》2016,361(7):239

  相似文献