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1.
Salini Thaliyakkattil Chandran Smitha Bal Raj Sajeev Ravindran Sanjeevan Vellorkirakathil Narayana 《Ocean Dynamics》2018,68(7):801-815
Upper layer circulation, hydrography, and biological response of Andaman waters during winter monsoon are assessed based on the observations carried out onboard FORV Sagar Sampada during January 2009 and November–December 2011. Cool and dry air carried by the moderate winds (6 m/s) from north and northeast indicates the influence of northeast monsoon (NEM) in the area during the observation time. The characteristics of physical parameters and the water mass indicate that the southeastern side is dominated by the less saline water from South China Sea intruded through the Malacca Strait, whereas the northeast is influenced by the freshwater from Ayeyarwady-Salween river system. The western side of the Andaman and Nicobar Islands exhibits similar properties of Bay of Bengal (BoB) water as evidenced in the T-S relation. Circulation pattern is uniform for the upper 88 m and is found to be more geostrophic rather than wind driven. Magnitude of the current velocity varies between 100 and 900 mm/s in November–December 2011 with strong current (900 mm/s) near Katchal and Nancowry islands and 100 and 1000 mm/s in January 2009 recording strong current (1000 mm/s) near the Little Nicobar Island. The Andaman waters are observed as less productive during the season based on the satellite-derived surface chl-a (0.1–0.4 mg/m3) and column-integrated primary productivity (PP) (100–275 mgC/m2/d). 相似文献
2.
A new pattern-recognition algorithm detects approximately 90% of the mines hidden in the Coastal Systems Station Sonar0, 1, and 3 databases of cluttered acoustic images, with about 10% false alarms. Similar to other approaches, the algorithm presented here includes processing the images with an adaptive Wiener filter (the degree of smoothing depends on the signal strength in a local neighborhood) to remove noise without destroying the structural information in the mine shapes, followed by a two-dimensional FIR filter designed to suppress noise and clutter, while enhancing the target signature. A double peak pattern is produced as the FIR filter passes over mine highlight and shadow regions. Although the location, size, and orientation of this pattern within a region of the image can vary, features derived from higher order spectra (HOS) are invariant to translation, rotation, and scaling, while capturing the spatial correlations of mine-like objects. Classification accuracy is improved by combining features based on geometrical properties of the filter output with features based on HOS. The highest accuracy is obtained by fusing classification based on bispectral features with classification based on trispectral features. 相似文献
3.
D.K. Pal T. Bhattacharyya P. Chandran S.K. Ray P.L.A. Satyavathi S.L. Durge P. Raja U.K. Maurya 《Quaternary International》2009,209(1-2):6
Smectitic parent material from the weathering Deccan basalt has been deposited in the lower piedmont plains, valleys and microdepressions during a previous wetter climate. The cracking clay soils (Vertisols) were developed in such alluvium during drier climate of the Holocene period. In India they occur in humid tropical (HT), sub-humid moist (SHM), sub-humid dry (SHD), semi-arid moist (SAM), semi-arid dry (SAD) and arid dry (AD) climatic environments and thus indicate an array of soils in a climosequence.The soils show a change in their morphological, physical, chemical and micromorphological properties in the climosequence. Soils of HT climate are dominated by Ca++ ions in their exchange complex throughout depth. However, in the sub-humid climates Mg++ ions tend to dominate in the lower horizons. The sub-humid moist to aridic climatic environments caused a progressive formation of pedogenic calcium carbonates (PC) with the concomitant increase in Na+ ions in soil solution. This facilitated the translocation of Na-clay in the soil profile. This is responsible for the increase in pH, decrease in Ca/Mg ratio of exchange sites with depth and finally in the development of subsoil sodicity. The reduction in mean annual rainfall (MAR) from sub-humid moist to arid climates accelerated the formation of PC and thus the soils of semi-arid and arid climates (SAM, SAD and AD) are more calcareous and sodic than soils of other climates (SHM and SHD).Formation of PC, illuviation of clay and the development of subsoil sodicity are concurrent, contemporary and active pedogenetic processes operating during the climate change of the Holocene period. These processes impaired the hydraulic properties of soils in general, and in soils of drier climates in particular. As a result, cracking pattern, chemical composition and plasmic fabric were more modified in soils of the drier climates. Such modifications in soil properties have a place in the rationale of Vertisol order of the US Soil Taxonomy. The soils of wetter climates (HT, SHM and SHD) are grouped in Typic Haplusterts whereas the soils of drier climates (SAM, SAD and AD) are classified as Aridic Haplusterts, Sodic Haplusterts and Sodic Calciusterts. The present study demonstrates how the intrinsic soil properties of the cracking clay soils in a climosequence may help in inferring the change in climate in a geologic period. 相似文献
4.
Mechanism and geochemical implications of the Late Holocene organic carbon burial event: an example from the southwest coast of India 总被引：1，自引：0，他引：1
B. Ajaykumar Mahesh Mohan M. S. Shylesh Chandran K. K. Jayasooryan K. S. Unni A. P. Thomas 《Environmental Earth Sciences》2010,59(7):1409-1416
Carbonaceous clay found in the palaeo-deposits of Meenachil River basin was analysed for the total organic carbon, nitrogen
and textural characters. Radiocarbon dating of this clay formation and the embedded carbonized wood fragments was also done.
The values obtained for the organic carbon, nitrogen and C/N ratio of the carbonaceous clay exhibited a very remarkable range,
suggestive of different environmental conditions of formation. It is evident from the present study that since the lignin
and cellulose are the dominant components of terrestrial higher plants, allochthonous and submerged organic matter have high
C/N ratio. The radio carbon dating of the sediment and wood samples suggested that the palaeo-deposits of Meenachil River
basin were formed as result of many transgrassive–regressive episodes, which had started even before the formation of Vembanad
Lake. The formation of carbonaceous clay, as found sandwiched in palaeo-deposits, was due to the global eustatic sea-level
fluctuations and tectonism. 相似文献
5.
Dr. Thomas Mathai K. N. Rajarama Satish Kumar M. Suresh Chandran M. R. Asoka Kumar 《Marine Georesources & Geotechnology》2013,31(2):180-193
Offshore geotechnical surveys form part of an integrated investigation to rejuvenate a decrepit minor port at Badagara, Kerala on the southwestern coast of India. The sediments typify a fluvio-marine milieu ranging from silty clay, sand, silty sand, sandy silt and clayey silt. Geotechnical and sedimentological studies of shallow cores reveal the geotechnical aspects besides the depositional history of the sediments. Downcore geotechnical variations and regressive coefficients based on their inter-relationships highlight diverse factorial inferences. X-Ray Diffraction data indicate the prominent clay type. A comparative evaluation of the geotechnical characteristics of clayey sediments off Badagara, with similar studies along various sectors of the Kerala coast, both on land as well as in the near shore, is broadly attempted. Geotechnical studies carried out earlier on the uplifted Cochin marine clays provide comparative data for evaluating the possible variations between present day marine clayey sediments occurring along the Kerala coast and uplifted marine clays which, besides their gross variations in levels with respect to the present sea-level, also obviously relate to a much older depositional environment and provenance during probable Holocene times. 相似文献
6.
Earthquakes cause massive road damage which in turn causes adverse effects on the society. Previous studies have quantified
the damage caused to residential and commercial buildings; however, not many studies have been conducted to quantify road
damage caused by earthquakes. In this study, an attempt has been made to propose a new scale to classify and quantify the
road damage due to earthquakes based on the data collected from major earthquakes in the past. The proposed classification
for road damage due to earthquake is called as road damage scale (RDS). Earthquake details such as magnitude, distance of
road damage from the epicenter, focal depth, and photographs of damaged roads have been collected from various sources with
reported modified Mercalli intensity (MMI). The widely used MMI scale is found to be inadequate to clearly define the road
damage. The proposed RDS is applied to various reported road damage and reclassified as per RDS. The correlation between RDS
and earthquake parameters of magnitude, epicenter distance, hypocenter distance, and combination of magnitude with epicenter
and hypocenter distance has been studied using available data. It is observed that the proposed RDS correlates well with the
available earthquake data when compared with the MMI scale. Among several correlations, correlation between RDS and combination
of magnitude and epicenter distance is appropriate. Summary of these correlations, their limitations, and the applicability
of the proposed scale to forecast road damages and to carry out vulnerability analysis in urban areas is presented in the
paper. 相似文献
7.
D. Ramakrishnan K. K. Mohanty S. R. Nayak R. Vinu Chandran 《Geotechnical and Geological Engineering》2006,24(6):1581-1602
The Bhuj earthquake (Mw = 7.9) occurred in the western part of India on 26th January 2001 and resulted in the loss of 20,000
lives and caused extensive damage to property. Soil liquefaction related ground failures such as lateral spreading caused
significant damage to bridges, dams and other civil engineering structures in entire Kachchh peninsula. The Bhuj area is a
part of large sedimentary basin filled with Jurassic, Tertiary and Quaternary deposits. This work pertains to mapping the
areas that showed sudden increase in soil moisture after the seismic event, using remote sensing technique. Multi-spectral,
spatial and temporal data sets from Indian Remote Sensing Satellite are used to derive the Liquefaction Sensitivity Index
(LSeI). The basic concept behind LSeI is that the near infrared and shortwave infrared regions of electromagnetic spectrum
are highly absorbed by soil moisture. Thus, the LSeI is herein used to identify the areas with increase in soil moisture after
the seismic event. The LSeI map of Bhuj is then correlated with field-based observation on Cyclic Stress Ratio (CSR) and Cyclic
Resistance Ratio (CRR), depth to water table, soil density and Liquefaction Severity Index (LSI). The derived LSeI values
are in agreement with liquefaction susceptible criteria and observed LSI (R
2 = 0.97). The results of the study indicate that the LSeI after calibration with LSI can be used as a quick tool to map the
liquefied areas. On the basis of LSeI, LSI, CRR, CSR and saturation, the unconsolidated sediments of the Bhuj area are classified
into three susceptibility classes. 相似文献
8.
B. Ajay Kumar Girish Gopinath M. S. Shylesh Chandran 《Arabian Journal of Geosciences》2014,7(5):1763-1772
The variability in ground water potential at different regions of the Meenachil River basin and the remarkable distribution of palaeodeposit of sand at its middle to lower reaches have led to interpret the sinuosity indexes of the main channel as well as the tributaries of the River for elucidating the relationship between mathematical expressions and filed observations. The measurement of digital elevation model-derived river sinuosity was carried out for 846 km2 of the basin area of Meenachil River. The drainage networks of 10 major sub-watersheds and four mini-watersheds were delineated using remote sensing data—geocoded false colour composite of Indian Remote Sensing satellite (IRS)-1D (LISS III) data with a spatial resolution of 23.5 m—coupled with the Survey of India toposheets (1:50,000). The calculation of the sinuosity indexes were carried out using Arc GIS (8.3 version) software. Hydraulic sinuosity indexes, topographic sinuosity index and standard sinuosity index were calculated. The study depicts the remarkable correlation between theoretical data sets with field observations and the influence of tectonic control on river planforms. Three structurally controlled regions of Meenachil River basin were established using Remote Sensing and Geographical Information System. 相似文献
9.
Thomas Mathai M. Suresh Chandran S. B. Nair M. R. Asoka Kumar Satish Kumar P. Praveen Kumar K. N. Rajarama T. Stephen George 《Marine Georesources & Geotechnology》2007,25(3):151-165
Sediment core samples collected during geotechnical surveys along the West Coast of India in the near shore areas of Arabian Sea have generated data on the geotechnical index properties of clayey sediments up to nearly 5 m depth below seafloor. A comparative study of three sectors within themselves is attempted before carrying out a final evaluation between the sectors. Cohesive clayey sediments of Gujarat sector are comparable though widely variant in a few aspects; in the Maharashtra-Goa-Karnataka sector though, plasticity levels and clay type vary, and activity and consistency levels are quite similar. Though broadly comparable, the clayey sediments of Kerala-Tamilnadu sector have quite diverse characteristics that fail to conform to any particular pattern as each area has an exclusive set of geotechnical properties. 相似文献
10.
The effects of rotation and magnetic field on the Couette flow of an electrically-conducting fluid between two parallel plates have been discussed when one of the plates has been set into impulsive motion. Under the assumption of negligible induced magnetic field and the applied field being fixed relative to the moving plate, the governing momentum equations have been solved exactly, and the expressions for velocity and skin friction have been presented. The variations of velocity and skin friction have been discussed for different parameter values. The decrease in velocity due to rotation and its increase due to magnetic field have been shown. 相似文献