Homogeneous region determination using linear and nonlinear techniques   总被引：1，自引：0，他引：1  

Janaki Ballav Swain  Mrunmayee Manjari Sahoo  Kanhu Charan Patra 《自然地理学》2016,37(5):361-384

Similarity between catchments in a region can be determined depending on catchment properties. This helps to understand the response behavior of the similar catchments more appropriately. Catchment classification plays a major role in the process of hydrological prediction in the case of ungauged catchments. The following categorization was carried out for 32 catchments of India. Principal Component Analysis (PCA) along with K-means clustering, was applied as linear classification; and Self-Organizing Map (SOM) and Kernel Principal Component Analysis (KPCA) were implemented as nonlinear classification methods on catchment attributes and daily streamflow time series. The classification established on streamflow signatures was taken as the reference classification. Results obtained from PCA, SOM, and KPCA were compared with results of the reference classification. The absence of discordant catchments from the clusters of SOM, based on catchment attributes, suggests homogeneity among SOM-derived clusters. Similarity index scores are 0.48 and 0.47, 0.46 and 0.42 ?for first, second, third and fourth clusters of SOM respectively with that of the reference classification technique. Nonlinear techniques with high similarity index values outperformed standard techniques. This study demonstrated the ability of classification based on catchment attributes to classify ungauged catchments.  相似文献   

Trends and Change-Point in Satellite Derived Phenology Parameters in Major Wheat Growing Regions of North India During the Last Three Decades     

Debasish Chakraborty  Vinay Kumar Sehgal  Rajkumar Dhakar  Deb Kumar Das  Rabi Narayan Sahoo 《Journal of the Indian Society of Remote Sensing》2018,46(1):59-68

The virtual certainty of the anticipated climate change will continue to raise many questions about its aggregated impact of environmental changes on our regional food security in imminent future. Crop responses to these changes are certain, but its exact characteristics are hardly understood at regional scale due to complex overlapping effects of climate change and anthropogenic manipulation of agro-ecosystem. This study derived phenology of wheat in north India from satellite data and analyzed trends of phenology parameters over last three decades. The most striking change-point period in phenology trends were also derived. The phenology was derived from two sources: (1) STAR-Global vegetation Health Products-NDVI, and (2) GIMMS-NDVI. The results revealed significant earliness in start of growing season (SOS) in Punjab and Haryana while delay was found in Uttar Pradesh (UP). End of the wheat season almost always occurred early, to even those place where SOS was delayed. Length of growing season increased in most of Punjab and northern Haryana whereas its decrease dominated in UP. The early sowing practice of the farmers of the Punjab and Haryana may be one of the adaptation strategies to manage the terminal heat stress in reproductive stage of the crop in the region. The change-point occurred in late 1990s (1998–2000) in Punjab and Haryana, while in eastern UP it was in early 1990s (1990–1995). Despite the difference in temporal aggregation and spatial resolution, both the datasets yielded similar trends, confirming both the robustness of the results and applicability of the datasets over the region. The results demands further research for proper attribution of the effects into its causes and may help devising crop adaption practices to climatic stresses.  相似文献   

Phase separation of ore forming fluid related to gold mineralization in Wynad Gold Field,Southern Granulite Terrain,India: Evidences from fluid inclusion studies     

Ajit Kumar Sahoo  R. Krishnamurthi  Saju Varghese 《Geology of Ore Deposits》2015,57(6):522-535

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Observed and simulated water and energy budget components at SCAN sites in the lower Mississippi Basin     

Gabriëlle J. M. De Lannoy  Julie Ufford  Alok K. Sahoo  Paul Dirmeyer  Paul R. Houser 《水文研究》2011,25(4):634-649

Land surface models are typically constrained by one or a few observed variables, while assuming that the internal water and energy partitioning is sensitive to those observed variables and realistic enough to simulate unobserved variables. To verify these assumptions, in situ soil climate analysis network (SCAN) observations in the Lower Mississippi Basin (2002–2008) are analysed to quantify water and energy budget components and they are compared to Community Land Model (CLM3·5) simulations. The local soil texture is identified as a major indicator for water storage characteristics and the Normalized Difference Vegetation Index shows potential as a drought indicator in summer months. Both observations and simulations indicate a regime where, except in some summer months, evapotranspiration controls soil moisture. CLM simulations with different soil texture assignments show discharge sensitivity to soil moisture, but almost no impact on evapotranspiration and other energy balance components. The observed and simulated water budgets show a similar partitioning. However, the SCAN observed water balance does not close because of precipitation measurement errors, unobserved irrigation, lack of specific storage change measurements and errors in the computed actual evapotranspiration. The simulated heat flux partitioning differs from that ‘observed’, with a larger (resp. smaller) fraction of net radiation being used by latent (resp. sensible) heat flux, and unobserved freeze and thaw events. The comparison between observations and model simulations suggests that a consistent observation collection for multiple variables would be needed to constrain and improve the full set of land surface variable estimates. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Gravity wave interaction with floating membrane due to abrupt change in water depth   总被引：1，自引：0，他引：1  

D. Karmakar  T. Sahoo   《Ocean Engineering》2008,35(7):598-615

Using the recently developed expansion formulae for wave structure interaction problems, the scattering of surface water waves by a semi-infinite floating membrane due to abrupt change in bottom topography is analyzed. Both the cases of finite and infinite steps are analyzed. In the present paper, the analysis is based on the linearized theory of water waves and small amplitude membrane response. Combining the linearized kinematic and dynamic surface conditions on the water surface with the dynamic pressure condition on the membrane, a third order differential equation is derived to describe the membrane covered free surface condition. General wave energy relation for wave scattering by floating horizontal membrane is derived by the application of law of conservation of energy flux and alternately by the direct application of Green's second identity. In the floating membrane covered region, the wave energy density is a combination of the kinetic and potential energy density due to the surface gravity waves, and the surface energy density which is due to the existence of the floating membrane on the free surface. Gravity wave transformations due to an abrupt change in bottom topography in the presence of a floating membrane in finite water depth are analyzed based on shallow water approximation. Numerical results are computed and analyzed to understand the wave transformation due to the floating membrane when there is an abrupt change in topography in different cases.  相似文献   

Comparison of stress-dependent geophysical,hydraulic and mechanical properties of synthetic and natural sandstones for reservoir characterization and monitoring studies     

Ismael Himar Falcon-Suarez  Kelvin Amalokwu  Jordi Delgado-Martin  Ben Callow  Katleen Robert  Laurence North  Sourav K. Sahoo  Angus I. Best 《Geophysical Prospecting》2019,67(4):784-803

Synthetic rock samples can offer advantages over natural rock samples when used for laboratory rock physical properties studies, provided their success as natural analogues is well understood. The ability of synthetic rocks to mimic the natural stress dependency of elastic wave, electrical and fluid transport properties is of primary interest. Hence, we compare a consistent set of laboratory multi-physics measurements obtained on four quartz sandstone samples (porosity range 20–25%) comprising two synthetic and two natural (Berea and Corvio) samples, the latter used extensively as standards in rock physics research. We measured simultaneously ultrasonic (P- and S-wave) velocity and attenuation, electrical resistivity, permeability and axial and radial strains over a wide range of differential pressure (confining stress 15–50 MPa; pore pressure 5–10 MPa) on the four brine saturated samples. Despite some obvious physical discrepancies caused by the synthetic manufacturing process, such as silica cementation and anisotropy, the results show only small differences in stress dependency between the synthetic and natural sandstones for all measured parameters. Stress dependency analysis of the dry samples using an isotropic effective medium model of spheroidal pores and penny-shaped cracks, together with a granular cohesion model, provide evidence of crack closure mechanisms in the natural sandstones, seen to a much lesser extent in the synthetic sandstones. The smaller grain size, greater cement content, and cementation under oedometric conditions particularly affect the fluid transport properties of the synthetic sandstones, resulting in lower permeability and higher electrical resistivity for a similar porosity. The effective stress coefficients, determined for each parameter, are in agreement with data reported in the literature. Our results for the particular synthetic materials that were tested suggest that synthetic sandstones can serve as good proxies for natural sandstones for studies of elastic and mechanical properties, but should be used with care for transport properties studies.  相似文献   

Relationship of bidirectional reflectance of wheat with biophysical parameters and its radiative transfer modeling using PROSAIL     

D. Barman  V. K. Sehgal  R. N. Sahoo  S. Nagarajan 《Journal of the Indian Society of Remote Sensing》2010,38(1):35-44

The algorithms for deriving vegetation biophysical parameters rely on the understanding of bi-directional interaction of radiation and its subsequent linkages with canopy radiative transfer models and their inversion. In this study, an attempt has been made to define the geometry of sensor and source position to best relate plant biophysical parameters with bidirectional reflectance of wheat varieties varying in canopy architecture and to validate the performance of PROSAIL (PROSPECT+SAIL) canopy radiative transfer model. A field experiment was conducted with two wheat cultivars varying in canopy geometry and phenology. The bidirectional measurements between 400nm–1100nm at 5nm interval were recorded every week at six view azimuth and four view zenith positions using spectro-radiometer. Canopy biophysical parameters were recorded synchronous to bi-directional reflectance measurements. The broadband reflectances were used to compute the NDVIs which were subsequently related to leaf area index and biomass. Results showed that the bidirectional reflectance increased with increase in view zenith from 20⁰ to 60⁰ irrespective of the sensor azimuth. For a given view zenith, the reflectance was observed to be maximum at 150⁰ azimuth where the difference between the sun and sensor azimuth was least. For sun azimuth of 160⁰ and zenith of 52⁰, the view geometry defined by 150⁰ azimuth and 50⁰ zenith corresponded to hotspot position. The measured bidirectional NDVI had significant logarithmic relationship with LAI and linear relationship with biomass for both the varieties of wheat and maximum correlation of NDVI with LAI and with biomass was obtained at the hotspot position. The PROSAIL validation results showed that the model simulated well the overall shape of spectra for all combination of view zenith and azimuth position for both wheat varieties with overall RMSE less than 5 per cent. The hotspot and dark spot positions were also well simulated and hence model performance may be suitable for deriving wheat biophysical parameters using satellite derived reflectances.  相似文献   

Future Scenarios of Environmental Vulnerability Mapping Using Grey Analytic Hierarchy Process     

Sahoo  Satiprasad  Dhar  Anirban  Debsarkar  Anupam  Kar  Amlanjyoti 《Natural Resources Research》2019,28(4):1461-1483

Any sustainable resource utilization plan requires evaluation of the present and future environmental impact. The present research focuses on future scenario generation of environmental vulnerability zones based on grey analytic hierarchy process (grey-AHP). Grey-AHP combines the advantages of grey clustering method and the classical analytic hierarchy process (AHP). Environmental vulnerability index (EVI) considers twenty-five natural, environmental and anthropogenic parameters, e.g. soil, geology, aspect, elevation, slope, rainfall, maximum and minimum temperature, normalized difference vegetation index, drainage density, groundwater recharge, groundwater level, groundwater potential, water yield, evapotranspiration, land use/land cover, soil moisture, sediment yield, water stress, water quality, storage capacity, land suitability, population density, road density and normalized difference built-up index. Nine futuristic parameters were used for EVI calculation from the Dynamic Conversion of Land-Use and its Effects, Model for Interdisciplinary Research on Climate 5 and Soil and Water Assessment Tool. The resulting maps were classified into three classes: “high”, “moderate” and “low”. The result shows that the upstream portion of the river basin comes under the high vulnerability zone for the years 2010 and 2030, 2050. The effectiveness of zonation approach was between “better” and “common” classes. Sensitivity analysis was performed for EVI. Field-based soil moisture point data were utilized for validation purpose. The resulting maps provide a guideline for planning of detailed hydrogeological studies.

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The role of fault reactivation in the development of tropical montane lakes     

Pedro Walfir M. Souza-Filho  Roberto Vizeu L. Pinheiro  Francisco R. Costa  José Tasso F. Guimarães  Prafulla K. Sahoo  Marcio S. Silva  Cleverson G. Silva 《地球表面变化过程与地形》2020,45(14):3732-3746

This work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho-structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion by – and building of – the formation of the South Carajás Hill; (iii) Fe-rich crust formation by weathering and gravitational collapse faults following the E–W plateau border and the start of Violão Lake formation during the Pliocene–Pleistocene; and (iv) episodic fault-fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake-level fluctuations. Initial fault reactivation under low-level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine-grained sediments from dilute interflows or overflows until 36 000 cal year BP. At about 31 000 cal year BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation. © 2020 John Wiley & Sons, Ltd.  相似文献   

3D Subsurface Characterization of Banded Iron Formation Mineralization using Large-Scale Gravity Data: A Case Study in Parts of Bharatpur,Dausa and Karauli Districts of Rajasthan,India     

Sahoo  Saudamini  Singh  Anand  Biswas  Santu  Sharma  S. P. 《Natural Resources Research》2021,30(5):3121-3138

Our study interprets large-scale gravity data to delineate concealed banded iron formation (BIF) iron mineralization in India's Rajasthan province. The study area belongs to the Bharatpur, Dausa, and Karauli districts of Rajasthan. We measured 1462 gravity readings to understand the rock types, depth and geometry of the different rock formations in the proposed study area. We also collected representative lithologies from more than 100 locations in the study area and calculated their density values. The measured gravity datasets are investigated via qualitative (e.g., Bouguer anomaly, first derivative and second derivative) and quantitative (radially averaged power spectrum, 3D Euler deconvolution, and 3D inversion) approach. The qualitative methods suggest a general NE–SW orientation of the BIFs, controlled by the general trend of the study area's structural setting. The lithological contact between the Bhilwara and Vindhyan Supergroups is demarcated by a NE–SW trending steep gravity gradient zone. In this area, representative lithologies yield high densities (about 3.746 gm/cc), and the samples identified as BIF represent exploration targets for iron ore. We have also developed our own in-house 3D gravity inversion code in this study. A model space inversion algorithm is converted into a data space using the identity relationship. It makes inversion algorithm very user-friendly on conventional desktop computers. The outcomes from the 3D inversion suggest that the concealed iron ore thickens to the west. This interpretation is also in good correlation with Euler 3D deconvolution of the gravity data.

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