Evaluation of groundwater potential zones using Remote Sensing data in upper Vaigai river basin,Tamil Nadu,India   总被引：1，自引：0，他引：1  

K Sankar 《Journal of the Indian Society of Remote Sensing》2002,30(3):119-129

The area of upper Vaigai river basin covering parts of Madurai and Theni Districts, in Tamil Nadu, faces acute water scarcity and chronically drought prone. The groundwater resources in the area have not been fully exploited. The present investigation has been made to evaluate the potential zones for groundwater targeting using IRS - ID LISS III geocoded data on 1:50,000 scale. The geology, geomorphology, lineament tectonic maps are generated and integrated to evaluate the hydrogeomorphological characteristics of the upper Vaigai river basin and demarcate the groundwater potential zones. A number of geomorphic units have been observed. Out this the more groundwater prospective units are buried pediment medium, buried pediment deep, flood plain, bajada and lineament and intersection of lineaments. Non potential areas like pediment, pediment inselberg, shallow pediment and pediplain were identified.  相似文献   

Detection of seismic reflections from seismic attributes through fractal analysis   总被引：5，自引：0，他引：5  

Sankar Kumar Nath  Pawan Dewangan 《Geophysical Prospecting》2002,50(3):341-360

The concept of fractals is used here for the identification of seismic reflectors with special emphasis on thin‐bed delineation, which is generally overlooked during standard data processing. A new fractal analysis scheme is applied to both synthetic and real field seismic data. The fractal dimensions of the three seismic attributes – amplitude, phase, and instantaneous frequency – have been analysed and evaluated. A change in fractal dimension is found to occur whenever there is a reflection. However, the resolution in the delineation of reflectors varies, depending on the attribute under consideration and the method of fractal dimension estimation used. Fractal analysis is performed on both noise‐free and noisy synthetic data to establish the noise tolerance limit for both the ‘divider method’ and the ‘Hurst method’. It is then tested with different peak frequencies of the source wavelet to establish the criteria for using the divider method and the Hurst method. The divider method is found to be suitable for high peak frequency source wavelets (> 25 Hz), while the Hurst method is best suited for low peak frequency source wavelets (< 25 Hz). Finally, when applied to the digitally processed and migrated field seismic data, it could even delineate reflectors which otherwise went undetected on the migrated time section.  相似文献   

Evolution of Mayurbhanj Granite Pluton, eastern Singhbhum, India: a case study of petrogenesis of an A-type granite in bimodal association     

Saumitra Misra  Subha Sankar Sarkar  Sambhunath Ghosh 《Journal of Asian Earth Sciences》2002,20(8)

The A-type Mayurbhanj Granite Pluton (3.09 Ga), occurring along the eastern margin of the Singhbhum-Orissa Craton, eastern India, represents the final phase of acid plutonism in this crustal block of Archean age. The granite shows a bimodal association with a voluminous gabbroid body, exposed mainly along its western margin, and is associated with the Singhbhum Shear zone. The granite pluton is composed mainly of a coarse ferrohastingsite–biotite granite phase, with an early fine-grained granophyric microgranitic phase and a late biotite aplogranitic phase. Petrogenetic models of partial melting, fractional crystallisation and magma mixing have been advocated for the evolution of this pluton. New data, combined with earlier information, suggest that two igneous processes were responsible for the evolution of the Mayurbhanj Granite Pluton: partial melting of the Singhbhum Granite; followed by limited amount of mixing of acid and basic magmas in an anorogenic extensional setting. The necessary heat for partial melting was provided by the voluminous basaltic magma, now represented by the gabbroid body, emplaced at a shallow crustal level and showing a bimodal association with the Mayurbhanj Granite Pluton. The Singhbhum Shear Zone provided a possible channel way for the emplacement of the basic magma during crustal extension. It is concluded that all three phases of the Mayurbhanj Granite Pluton were derived from the same parent magma, generated by batch partial melting of the Singhbhum Granite at relatively high temperatures (980 °C) and low pressures (4 to <2 kbar) under anhydrous conditions. The coarse ferrohastingsite biotite granite phase shows evidence of limited and heterogeneous assimilation of country rock metasediments. However, the early microgranite phase and late aplogranite phase have not assimilated any metasediments. Compositional irregularities observed along the western margin of the Mayurbhanj Granite Pluton in contact with the gabbro body including a continuous fractionating sequence from quartz diorite to alkali-feldspar granite in the Notopahar area. Gradational contacts between the gabbro and the Mayurbhanj Granite Pluton in the Gorumahisani area etc., may be attributed to a limited amount of mixing between the gabbroid magma and the newly generated Mayurbhanj Granite magma. The mixing was mainly of liquid–liquid diffusive type, with a subordinate amount of mixing of solid–liquid type. Although A-type granites are commonly described as having high total REE (e.g. 270–400 ppm), studies on the late aplogranite phase of the Mayurbhanj Granite show that total REE values (100 ppm) are low. This low REE abundance may be attributed to the progressive residual nature of the Singhbhum Granite source during continued partial melting, when the magmas of the microgranite and coarse granite phases had already been removed from the source region.  相似文献   

Spatio-temporal analysis of decadal-scale patterns in barrier island response to storms: Perdido Key,NW Florida     

Ravi D. Sankar  Joseph F. Donoghue  Stephen A. Kish 《自然地理学》2018,39(2):166-195

The ability to accurately quantify shoreline variability is essential in order to establish aggressive mitigation strategies, based on recent global climate change projections. This investigation employed a suite of coastal data (topographic maps, aerial photography, satellite imagery and lidar) to establish decadal trends of shoreline movement along Perdido Key, a sandy barrier island off Florida’s northwest coast. The technique used to detect morphologic change with time was a recently developed tool, Analyzing Moving Boundaries Using R. This innovative methodology improves our understanding of the evolution of coastal systems by modeling shoreline variance using a method that is sensitive to shoreline shape. Results show that the barrier shoreline is a highly dynamic feature with distinct zones of erosion and accretion that are pervasive over time. In general, the island is displaying a mechanism of rotational instability with the eastern half retreating, and the western portion advancing. The inflection point, around which this rotational shifting is taking place, lies at the center of a Pleistocene headland located along the island’s midpoint. The results of this study suggest that coastal evolution along the island may be meta-stable, with trends in shoreline variance corresponding mainly to discrete storm events in time.  相似文献   

Soil organic carbon mapping using remote sensing techniques and multivariate regression model     

Gouri Sankar Bhunia  Hamid Reza Pourghasemi 《国际地球制图》2019,34(2):215-226

Soil organic carbon (SOC) is an important aspect of soil quality and plays an imperative role in soil productivity in the agriculture ecosystems. The present study was applied to estimate the SOC stock using space-borne satellite data (Landsat 4–5 Thematic Mapper [TM]) and ground verification in the Medinipur Block, Paschim Medinipur District and West Bengal in India. In total, 50 soil samples were collected randomly from the region according to field surveys using a hand-held Global Positioning System (GPS) unit to estimate the surface SOC concentrations in the laboratory. Bare soil index (BSI) and normalized difference vegetation ndex (NDVI) were explored from TM data. The satellite data-derived indices were used to estimate spatial distribution of SOC using multivariate regression model. The regression analysis was performed to determine the relationship between SOC and spectral indices (NDVI and BSI) and compared the observed SOC (field measure) to predict SOC (estimated from satellite images). Goodness fit test was performed to determine the significance of the relationship between observed and predicted SOC at p ≤ 0.05 level. The results of regression analysis between observed SOC and NDVI values showed significant relationship (R² = 0.54; p < 0.0075). A significant statistical relationship (r = ?0.72) was also observed between SOC and BSI. Finally, our model showed nearly 71% of the variance of SOC distribution could be explained by SOC and NDVI values. The information from this study has advanced our understanding of the ongoing ecological development that affects SOC dissemination and might be valuable for effective soil management.  相似文献   

Mapping of rock types using a joint approach by combining the multivariate statistics,self-organizing map and Bayesian neural networks: an example from IODP 323 site     

Mampi Karmakar  Saumen Maiti  Amrita Singh  Maheswar Ojha  Bhabani Sankar Maity 《Marine Geophysical Researches》2018,39(3):407-419

Modeling and classification of the subsurface lithology is very important to understand the evolution of the earth system. However, precise classification and mapping of lithology using a single framework are difficult due to the complexity and the nonlinearity of the problem driven by limited core sample information. Here, we implement a joint approach by combining the unsupervised and the supervised methods in a single framework for better classification and mapping of rock types. In the unsupervised method, we use the principal component analysis (PCA), K-means cluster analysis (K-means), dendrogram analysis, Fuzzy C-means (FCM) cluster analysis and self-organizing map (SOM). In the supervised method, we use the Bayesian neural networks (BNN) optimized by the Hybrid Monte Carlo (HMC) (BNN-HMC) and the scaled conjugate gradient (SCG) (BNN-SCG) techniques. We use P-wave velocity, density, neutron porosity, resistivity and gamma ray logs of the well U1343E of the Integrated Ocean Drilling Program (IODP) Expedition 323 in the Bering Sea slope region. While the SOM algorithm allows us to visualize the clustering results in spatial domain, the combined classification schemes (supervised and unsupervised) uncover the different patterns of lithology such of as clayey-silt, diatom-silt and silty-clay from an un-cored section of the drilled hole. In addition, the BNN approach is capable of estimating uncertainty in the predictive modeling of three types of rocks over the entire lithology section at site U1343. Alternate succession of clayey-silt, diatom-silt and silty-clay may be representative of crustal inhomogeneity in general and thus could be a basis for detail study related to the productivity of methane gas in the oceans worldwide. Moreover, at the 530 m depth down below seafloor (DSF), the transition from Pliocene to Pleistocene could be linked to lithological alternation between the clayey-silt and the diatom-silt. The present results could provide the basis for the detailed study to get deeper insight into the Bering Sea’ sediment deposition and sequence.  相似文献   

Investigation of Hemispherical Variations of Soft X-Ray Solar Flares during Solar Cycles 21 to 24     

Prasad  Amrita  Roy  Soumya  Ghosh  Koushik  Panja  Subhash Chandra  Patra  Sankar Narayan 《Solar System Research》2021,55(2):169-182

Solar System Research - In the current investigation we have studied the distribution as well as the asymmetry of solar X-ray flares during the period 1976–2017 which corresponds to solar...  相似文献   

A study of self-similar cylindrical MHD shock waves in monochromatic radiation     

Onkar Nath 《Astrophysics and Space Science》1989,158(1):163-167

It is never too strange to expect that an eventual fifth repulsive interaction may also be mediated by a spin-2 field. On the other hand, it is highly unlikely that a spin-1 field may mediate an attractive force.  相似文献   

First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS)   总被引：2，自引：4，他引：2  

William K. Mohanty  M. Yanger Walling  Sankar Kumar Nath  Indrajit Pal 《Natural Hazards》2007,40(2):245-260

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of M_w 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.  相似文献   

Sunyaev–Zel'dovich distortion from early galactic winds     

Subhabrata Majumdar  Biman B. Nath  Masashi Chiba 《Monthly notices of the Royal Astronomical Society》2001,324(3):537-546

We consider the distortion in the cosmic microwave background (CMB) resulting from galactic winds at high redshift. Winds outflowing from galaxies have been hypothesized to be possible sources of metals in the intergalactic medium, which is known to have been enriched to 10^−2.5 Z_⊙ at z ∼3. We model these winds as functions of mass of the parent galaxy and redshift, assuming that they activate at a common initial redshift, z _in, and calculate the mean y -distortion and the angular power spectrum of the distortion in the CMB. We find that the thermal Sunyaev–Zel'dovich (SZ) effect resulting from the winds is consistent with previous estimates. The distortion arising from the kinetic SZ (kSZ) effect is, however, found to be more important than the thermal SZ (tSZ) effect. We find that the distortion resulting from galactic winds is an important contribution to the power spectrum of distortion at very small angular scales ( l ∼10⁴). We also find that the power spectrum resulting from clustering dominates the Poisson power spectrum for l ≤(4–5)×10⁵. We show explicitly how the combined power spectrum from wind dominates over that of clusters at 217 GHz, relevant for PLANCK . We also show how these constraints change when the efficiency of the winds is varied.  相似文献