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31.
D. Bala Subrahamanyam Radhika Ramachandran K. Sen Gupta Tuhin K. Mandal 《Boundary-Layer Meteorology》2003,107(3):683-695
The upper air data collected from the balloon-borne GLASS Sondes launched from the Oceanic Research Vessel (ORV) Sagar Kanya during the Intensive Field Phase of the Indian Ocean experiment (INDOEX, IFP-99;SK-141 Cruise) are utilized forstudying the variability in the mixed-layer heights observed over the western tropical Indian Ocean and central Arabian Sea. During the entire cruise, typical daytime convective mixed-layer heights (roughly corresponding to 1400 LT) obtained from V and q profiles, were observed to be in the range 200–900 m. Shallowmixed -layer heights are observed, in general, over the Inter-Tropical Convergence Zone (ITCZ). Over the central Arabian Sea, vertical profiles of V and q demonstrate a double mixed-layer structure of the marine atmospheric boundary layer (MABL), which gradually disappears close to the Indian coastline. 相似文献
32.
Seismic reflection profiles from three different surveys of the Cascadia forearc are interpreted using P wave velocities and relocated hypocentres, which were both derived from the first arrival travel time inversion of wide-angle seismic data and local earthquakes. The subduction decollement, which is characterized beneath the continental shelf by a reflection of 0.5 s duration, can be traced landward into a large duplex structure in the lower forearc crust near southern Vancouver Island. Beneath Vancouver Island, the roof thrust of the duplex is revealed by a 5–12 km thick zone, identified previously as the E reflectors, and the floor thrust is defined by a short duration reflection from a < 2-km-thick interface at the top of the subducting plate. We show that another zone of reflectors exists east of Vancouver Island that is approximately 8 km thick, and identified as the D reflectors. These overlie the E reflectors; together the two zones define the landward part of the duplex. The combined zones reach depths as great as 50 km. The duplex structure extends for more than 120 km perpendicular to the margin, has an along-strike extent of 80 km, and at depths between 30 km and 50 km the duplex structure correlates with a region of anomalously deep seismicity, where velocities are less than 7000 m s− 1. We suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion. The absence of seismicity from within the E reflectors implies that they are significantly weaker than the overlying crust, and the reflectors may be a zone of active ductile shear. In contrast, seismicity in parts of the D reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex. Merging of the D and E reflectors at 42–46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km. We suggest that pervasive reflectivity in the upper mantle elsewhere beneath Puget Sound and the Strait of Georgia arises from similar shear zones. 相似文献
33.
34.
Dipnarayan Ganguly Anirban Mukhopadhyay Rahul Krishna Pandey Debasish Mitra 《Journal of the Indian Society of Remote Sensing》2006,34(4):431-435
Study of landforms in Sundarbans deltaic estuary is necessary in regular basis due to its importance and impact on ecology,
climate and economy. Remote sensing has proved as an important tool to study this. Multi-temporal satellite data helps to
delineate the various geomorphic classes in different time domain and also provide inputs to study the coastal erosion and
accretion. Finer spatial and better temporal resolution will be an added adventure for this kind of study. 相似文献
35.
Prakash Chauhan Shailesh Nayak R Ramesh R Krishnamoorthy S Ramachandran 《Journal of the Indian Society of Remote Sensing》1996,24(2):105-114
Indian Remote Sensing satellite (IRS) 1A & 1B digital data in combination with field measurement were used to map distribution and concentration of suspended sediments along the Tamil Nadu coastal waters for monsoon and non-monsoon periods. Qualitative suspended sediment mapping was done for entire Tamil Nadu coast while quantitative studies were taken at two selected sites (eg. Tuticorin and Ennore). For qualitative mapping both monsoon (17-12-90) and non-monsoon (18-4-90) season data were analysed by level slicing technique and a qualitative scale was assigned to different sediment classes based on tonal variations. The suspended sediment concentration (SSC) samples were collected on April 15, 1992 and March 10, 1992 around Ennore and Tuticorin coastal waters respectively, synchronous to IRS-1A satellite overpass. This data was used for quantitative estimation of SSC using digital chromaticity technique. The study shows that the plumes of high suspended sediment concentration are contributed from the nearshore wetlands and river mouths and were finally dispersing towards Jaffna coast. Different classes of high to low SSC values ranging from less than 5 mg/L in offshore areas to 21 mg/L in nearshore of Tuticorin were also delineated. The dispersal pattern of the sediments on different is discussed. 相似文献
36.
Shoreline and coral reef ecosystem changes in gulf of Mannar, Southeast coast of India 总被引:1,自引:0,他引:1
M. Thanikachalam S. Ramachandran 《Journal of the Indian Society of Remote Sensing》2003,31(3):157-173
Changes in shoreline, coral reef and seafloor have been mapped using remote sensing satellite data of IRS LISS-III (1998),
IRS LISS-II (1988), Survey of India Topographic sheet (1969), Naval Hydrographic Chart (NHO) 1975 and bathymetry data (1999)
with ARC-INFO and ARC-VIEW GIS. The analysis of multi-date shoreline maps showed that 4.34 and 23.49 km2 of the mainland coast
and 4.14 and 3.31 km2 areas of island coast have been eroded and accreted, respectively, in the Gulf of Mannar. The analysis of multi-date coral
reef maps showed that 25.52 km2 of reef area and 2.16 km2 of reef vegetation in Gulf of Mannar have been lost over a period of ten years. The analysis of multi-date bathymetry data
indicates that the depth of seafloor has decreased along the coast and around the islands in the study area. The average reduction
of depth in seafloor has been estimated as 0.51m over a period of twenty four years. The increased suspended sediment concentration
due to coastal and island erosion, and raised reef due to emerging of coast by tectonic movement are responsible for coral
reef degradation in the Gulf of Mannar. Validation by ground truth has confirmed these results. 相似文献
37.
K. Selvavinayagam A. Surendran S. Ramachandran 《Journal of the Indian Society of Remote Sensing》2003,31(3):227-235
Quantification of Chlorophyll using IRS-P4 OCM data was attempted. OCM-DAS software developed by Space Applications Centre,
Ahmedabad was used in data analysis. The results showed considerable variations in nearshore (case 2) waters due to interference
from yellow substance and suspended sediments. However, in offshore areas (case 1) the measurements showed good correlations.
The r values are 0.663 for nearshore waters and 0.892 for offshore waters. 相似文献
38.
Rahul Sharma B. Nagendernath A. B. Valsangkar G. Parthiban K. M. Sivakolundu Gavin Walker 《Marine Georesources & Geotechnology》2000,18(3):209-221
As a part of the Environmental Impact Assessment studies for nodule mining, a long-term program has been initiated in the Central Indian Basin. Multidisciplinary studies on geological, biological, physical, and chemical parameters were carried out in an area selected on the basis of baseline data collected in the first phase of the program. A benthic disturbance was simulated with a hydraulic device also used in the previous experiments in the Pacific Ocean. A site of 3,000 ×200 m was repeatedly disturbed by a combination of fluidizing pump and suction pump to dislodge and discharge sediment from the seafloor into the water column 5 m above the seafloor. During 9 days of operation, 26 tows were carried out for 47 h of disturbance, resuspending about 6,000 m 3 of sediment along an 88-km line. Data for postdisturbance impact assessment were collected with sediment traps, deep-towed cameras, seafloor samples, and conductivity-temperature depth sensor (CTD)-rosette observations. Seafloor data, sediment samples, and water column studies were aimed at evaluating the impact of benthic disturbance, on the basis of pre- and postdisturbance data collected during the experiment. Observations show that vertical mixing of sediment as well as its lateral movement and resedimentation because of plume migration alters various parameters and leads to changes in the environment around the area. 相似文献
39.
We perform large-eddy simulation (LES) of a moderately convective atmospheric boundary layer (ABL) using a prognostic subfilter-scale
(SFS) model obtained by truncating the full conservation equations for the SFS stresses and fluxes. The truncated conservation
equations contain production mechanisms that are absent in eddy-diffusivity closures and, thus, have the potential to better
parametrize the SFS stresses and fluxes. To study the performance of the conservation-equation-based SFS closure, we compare
LES results from the surface layer with observations from the Horizontal Array Turbulence Study (HATS) experiment. For comparison,
we also show LES results obtained using an eddy-diffusivity closure. Following past studies, we plot various statistics versus
the non-dimensional parameter, Λ
w
/Δ, where Λ
w
is the wavelength corresponding to the peak in the vertical velocity spectrum and Δ is the filter width. The LES runs are
designed using different domain sizes, filter widths and surface fluxes, in order to replicate partly the conditions in the
HATS experiment. Our results show that statistics from the different LES runs collapse reasonably and exhibit clear trends
when plotted against Λ
w
/Δ. The trends exhibited by the production terms in the modelled SFS conservation equations are qualitatively similar to those
seen in the HATS data with the exception of SFS buoyant production, which is underpredicted. The dominant production terms
in the modelled SFS stress and flux budgets obtained from LES are found to approach asymptotically constant values at low
Λ
w
/Δ. For the SFS stress budgets, we show that several of these asymptotes are in good agreement with their corresponding theoretical
values in the limit Λ
w
/Δ → 0. The modelled SFS conservation equations yield trends in the mean values and fluctuations of the SFS stresses and fluxes
that agree better with the HATS data than do those obtained using an eddy-diffusivity closure. They, however, underpredict
considerably the level of SFS anisotropy near the wall when compared to observations, which could be a consequence of the
shortcomings in the model used for the pressure destruction terms. Finally, we address the computational cost incurred due
to the use of additional prognostic equations. 相似文献
40.
It is shown how the computational burden of source localization by matched field processing (MFP) can be significantly reduced (20 to 30 times) by expressing the correlation in terms of a discrete Fourier transform and using the fast Fourier transform (FFT) algorithm. The price paid to achieve increased speed is in the form of quantization phase errors. It is shown through analysis and computer simulation that the quantization errors reduce the source peak height, depending upon the size of DFT. The proposed fast MFP works for range localization only. However, the depth estimation is possible by repeated application of the above algorithm for different depths 相似文献