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31.
Sandip R. Oza R. K. K. Singh N. K. Vyas B. S. Gohil Abhijit Sarkar 《Journal of the Indian Society of Remote Sensing》2011,39(2):147-152
The identification of sea-ice has frequently been cited as one of the most important tasks for deriving the sea-ice parameters
and to avoid erroneous retrieval of wind vector over sea-ice infested oceans using space-borne scatterometer data. Discrimination
between sea-ice and ocean is ambiguous under the high wind and/or thin/scattered ice conditions. The pre-launch technique
developed for Oceansat-2, utilizes the dual-polarized QuikSCAT scatterometer data by using the spatio-temporal coherence properties
of sea ice in addition to backscatter coefficient and the Active Polarization Ratio. Results were compared with the operational
sea-ice products from National Snow and Ice Data Center. The threshold API value of −0.025 was found optimum for sea-ice and
ocean discrimination. The overall sea-ice identification accuracy achieved was of the order of 95 per cent, ranging from 92.5%
(during December in Southern Hemisphere) to 98% (during March in Northern Hemisphere). The applicability of the algorithm
for both the Arctic as well as Antarctic makes it suitable for its operational use with the Oceansat-2 scatterometer data. 相似文献
32.
The grain-flow has so far been defined with reference to the distinctive sediment-support mechanism, the dispersive pressure. The role of sediment-support mechanism, however, is required in a multiphase flow to prevent the gravitational settling of the particles through the driving medium during the flow. In a single-phase flow of non-cohesive grains no such secondary mechanism is required to counteract the gravitational pull, the driving force of the flow. So the definition of grain-flow needs a critical revision. This, in turn, involves proper understanding of the grain-flow mechanism, so that the relation between the process and the product can be properly established. The most distinctive feature often demonstrated by a grain-flow deposit is the particle size segregation, which leads to the development of inverse grading. The available explanations for this phenomenon find theoretical constraints. In the present study an attempt was made to understand the mechanism of single-phase non-cohesive granular flow of different flow regime and the particle segregation pattern in the resultant deposit through laboratory simulation. The experimental observations revealed that no sustained granular flow sets in on a slope deviating much from the limiting value of the angle of repose of the granular material. A persistent simple shear flow develops on slopes of this critical value. Each of the grains rolls in response to simple shearing. If the shear stress attains a critical value, theoretically the larger grains can even climb up the adjacent smaller ones towards the down-slope direction. In reality, however, high angle climb is not very common. The larger grains preferably roll over the smaller grains when the common tangent becomes almost horizontal or makes a very low angle with the direction of flow, and by this process gradually reaches the upper surface of the flow causing the development of inverse grading. The upper surface of the resultant deposit remains parallel to the sloping substratum. These properties readily distinguish this variety of granular flow from the other natural flows, and the flow may thus be assigned the distinct status of grain-flow. 相似文献
33.
The western margin of Sundaland is affected by two major tectonic events, the India-Eurasia collision and subduction along the Burmese-Andaman-Sunda Arc. Geotectonic analysis of the Burmese-Andaman-Sunda Arc areas reveals that it represents an arc setting exposed both in land and sea environment. Within this broad arc setting, there are individual segments that illustrate discernible trends in terms of structural, seismic and geological characteristics. The Equatorial Region around Sumatra has some peculiar geological/geophysical characteristics that make it a tectonic hotspot. Here a relationship between the active volcanism and the development of forearc basins is established. It is also proposed that the downgoing oceanic plate is more strongly coupled to the overlying plate where it is youngest (~ 40 Ma), has the highest temperature and is topographically most elevated with highest seismic activity. In particular, an increase in convergence rate and presence of youngest oceanic crust appear to be the main controlling factor underpinning the tectonics and surge of recent seismic activity in Sumatra. 相似文献
34.
Groundwater discharge along a channelized Coastal Plain stream 总被引:1,自引:1,他引:0
Danita M. LaSage Joshua L. Sexton Abhijit Mukherjee Alan E. Fryar Stephen F. Greb 《Journal of Hydrology》2008,360(1-4):252-264
In the Coastal Plain of the southeastern USA, streams have commonly been artificially channelized for flood control and agricultural drainage. However, groundwater discharge along such streams has received relatively little attention. Using a combination of stream- and spring-flow measurements, spring temperature measurements, temperature profiling along the stream-bed, and geologic mapping, we delineated zones of diffuse and focused discharge along Little Bayou Creek, a channelized, first-order perennial stream in western Kentucky. Seasonal variability in groundwater discharge mimics hydraulic-head fluctuations in a nearby monitoring well and spring-discharge fluctuations elsewhere in the region, and is likely to reflect seasonal variability in recharge. Diffuse discharge occurs where the stream is incised into the semi-confined regional gravel aquifer, which is comprised of the Mounds Gravel. Focused discharge occurs upstream where the channel appears to have intersected preferential pathways within the confining unit. Seasonal fluctuations in discharge from individual springs are repressed where piping results in bank collapse. Thereby, focused discharge can contribute to the morphological evolution of the stream channel. 相似文献
35.
Characterization of tidally influenced seasonal nutrient flux to the Bay of Bengal and its implications on the coastal ecosystem 下载免费PDF全文
Submarine groundwater discharge (SGD) introduces solute and nutrients to the global oceans, resulting in considerable nutrient cycling and dynamics in the coastal areas. We have conducted high‐resolution, spatio‐temporal, lunar tidal cycle patterns and variability of discharged solute/nutrient assessment to get an overview of seasonal nutrient flux to the Bay of Bengal in eastern parts of the Indian subcontinent. Whereas the premonsoon season SGD was found to be dominant in the marine influence (M‐SGD), the postmonsoon season was found to be predominated by the terrestrial component of SGD (T‐SGD), extending from coast to near offshore. The solute fluxes and redox transformation were found to be extensively influenced by tidal and diurnal cycles, overlapping on seasonal patterns. We have assessed the possible role of SGD‐associated solute/nutrient fluxes and their discharge mechanisms, and their associated temporal distributions have severe implications on the biological productivity of the Bay of Bengal. The estimated annual solute fluxes, using the average end‐member concentration of the SGD‐associated nutrients, were found to be 240 and 224 mM·m?2·day?1 for NO3? and Fetot, respectively. Together with huge freshwater flux from the Himalayan and Peninsular Indian rivers, the SGD has considerable influence on the bay water circulation, stratification, and solute cycling. Thus, the observation from this study implies that SGD‐associated nutrient flux to the Bay of Bengal may function as a nutrient sink, which might influence the long‐term solute/nutrient flux along the eastern coast of India. 相似文献
36.
Acta Geotechnica - The forced vertical vibration tests were performed in the field on 3.3-m-long driven steel pipe on a single vertical pile, P1 (β?=?0°), and single batter... 相似文献
37.
The activity of a silicate liquid component in a melt at an elevated liquidus temperature and pressure may be expressed analytically in terms of the 1-bar liquidus temperature activity and functions of the partial molar volume and partial molar enthalpy of mixing. Alternatively, the activity of the elevated (i.e. higherP-T) liquidus may be expressed in terms of the difference of heat content, heat capacity, entropy and volume of the component in the crystalline form and in the melt. Equating these two expressions, the partial molar enthalpy of mixing and there-from the partial molar entropy of mixing may be determined, provided the liquidus temperatures of the phase in question at both 1 bar and higher pressure and at a constant melt composition are known. Several such retrievals for CaMgSi2O6, Mg2SiO4, NaAlSi3O8, and TiO2 from experimental phase equilibrium data are presented. It is argued that as the partial molar enthalpy of mixing generally has large values, the regular solution formulation on the basis of a constant function of the activity coefficient would lead to erroneousP-T estimates for ascending magmas. 相似文献
38.
Abhijit Basu 《Journal of Earth System Science》2005,114(3):375-380
Back scattered electron and transmission electron imaging of lunar soil grains reveal an abundance of submicrometer-sized
pure Fe0 globules that occur in the rinds of many soil grains and in the submillimeter sized vesicular glass-cemented grains called
agglutinates. Grain rinds are amorphous silicates that were deposited on grains exposed at the lunar surface from transient
vapors produced by hypervelocity micrometeorite impacts. Fe0 may have dissociated from Fe-compounds in a high temperature (>3000°C) vapor phase and then condensed as globules on grain
surfaces. The agglutinitic glass is a quenched product of silicate melts, also produced by micrometeorite impacts on lunar
soils. Reduction by solar wind hydrogen in agglutinitic melts may have produced immiscible droplets that solidified as globules.
The exact mechanism of formation of such Fe0 globules in lunar soils remains unresolved. 相似文献
39.
Auto-correlation analysis of wave heights in the Bay of Bengal 总被引:1,自引:0,他引:1
Time series observations of significant wave heights in the Bay of Bengal were subjected to auto-correlation analysis to determine
temporal variability scale. The analysis indicates an exponential fall of auto-correlation in the first few hours with a decorrelation
time scale of about six hours. A similar figure was found earlier for ocean surface winds. The nature of variation of auto-correlation
with time lags was also found to be similar for winds and wave heights 相似文献
40.
A two-dimensional numerical model is employed to study the effect of the coastal urban heat island on the sea breeze front
and the thermal internal boundary layer height. The temperature at the land surface is determined by solving an energy budget
equation. The effect of the urban heat island is studied by varying the width of the region and its intensity. During the
early afternoon, the presence of the urban heat island enhances the strength of convergence of the sea breeze front and also
reduces its inland penetration. The presence of the urban heat island causes increased thermal internal boundary layer height.
Larger urban width causes larger vertical velocity and higher thermal internal boundary layer. Stronger convergence and higher
thermal internal boundary layer are also obtained in case of larger heat island intensity. 相似文献