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Hareesh Kumar P.V.,Naval Physical and Oceanographic Laboratory | Hareesh Kumar P.V.,Naval Physical and Oceanographic Laboratory NPOL | Radhakrishnan K.G.,Naval Physical and Oceanographic Laboratory
Defence Science Journal | Year: 2010

Fine resolution spatial survey carried out off the west coast of India during June and December 2004 was utilised to study the transmission loss (TL) variability associated with the upwelling and downwelling processes in this region. During June, the upwelling was confined to the upper 80 m. Downsloping of isotherms below this depth towards the coast and the occurrence of low saline waters indicated the presence of undercurrent. Between the periods of upwelling and downwelling, temperature and salinity in the surface layers increased by 1-2 °C and 2 PSU, respectively, while at the sub-surface levels, the corresponding increase was -8 °C and ∼0.5 PSU. A range-dependent acoustic propagation model based on parabolic equation method was utilised to compute TL for these two periods. The model was run with a source frequency of 3 kHz kept at 5m depth for different environmental setup, viz. propagation along the constant-depth contour, range-independent and range-dependent environment, and upslope/downslope propagation. The computations revealed significant variability in the TL characteristics between the upwelling and downwelling scenario, though bathymetry and geo-acoustic properties were the same. The analysis also stressed the need of range-dependent acoustic propagation model for realistic prediction of transmission loss variability. © 2010, DESIDOC. Source

Ambat S.K.,Indian Institute of Science | Ambat S.K.,Naval Physical and Oceanographic Laboratory NPOL | Chatterjee S.,KTH Royal Institute of Technology | Hari K.V.S.,Indian Institute of Science
IEEE Transactions on Signal Processing | Year: 2014

Although many sparse recovery algorithms have been proposed recently in compressed sensing (CS), it is well known that the performance of any sparse recovery algorithm depends on many parameters like dimension of the sparse signal, level of sparsity, and measurement noise power. It has been observed that a satisfactory performance of the sparse recovery algorithms requires a minimum number of measurements. This minimum number is different for different algorithms. In many applications, the number of measurements is unlikely to meet this requirement and any scheme to improve performance with fewer measurements is of significant interest in CS. Empirically, it has also been observed that the performance of the sparse recovery algorithms also depends on the underlying statistical distribution of the nonzero elements of the signal, which may not be known a priori in practice. Interestingly, it can be observed that the performance degradation of the sparse recovery algorithms in these cases does not always imply a complete failure. In this paper, we study this scenario and show that by fusing the estimates of multiple sparse recovery algorithms, which work with different principles, we can improve the sparse signal recovery. We present the theoretical analysis to derive sufficient conditions for performance improvement of the proposed schemes. We demonstrate the advantage of the proposed methods through numerical simulations for both synthetic and real signals. © 2014 IEEE. Source

Kurahatti R.V.,Basaveshwar Engineering College | Kurahatti R.V.,National Institute of Technology Karnataka | Surendranathan A.O.,National Institute of Technology Karnataka | Kori S.A.,Basaveshwar Engineering College | And 5 more authors.
Defence Science Journal | Year: 2010

The potential opportunities promised by nanotechnology for enabling advances in defence technologies are staggering. Although these opportunities are likely to be realised over a few decades, many advantages are currently being explored, particularly for defence applications. This review provides an insight into the capabilities offered by nanocomposites which include smart materials, harder/lighter platforms, new fuel sources and storage as well as novel medical applications. It discusses polymer-based nanocomposite materials, nanoscale fillers and provides examples of the actual and potential uses of nanocomposite materials in defence with practical examples. © 2010, DESIDOC. Source

Swain J.,Naval Physical and Oceanographic Laboratory NPOL | Panigrahi J.K.,Nanyang Technological University | Umesh P.A.,Naval Physical and Oceanographic Laboratory NPOL | Baba M.,Indian Institute of Tropical Meteorology | And 2 more authors.
International Journal of Oceans and Oceanography | Year: 2013

With the launch of Oceansat-I (IRS-P4), it became a reality to carry out validations of third generation wave model 3g-WAM in the North Indian Ocean region using the IRS-P4 analyzed wind fields provided by the National Centre for Medium Range Weather Forecasting (NCMRWF), New Delhi, India. However, the model predicted wave fields were to be still analyzed and further validated using all available field measurements which was the primary task before the scientific community. This study, describes the wave model validation studies carried out at Naval Physical and Oceanographic Laboratory (NPOL), Cochin, India through a collaborative research programme between NPOL and Space Application Centre (SAC), as part of the IRS-P4, MSMR Utilization Programme. Under this collaborative programme, 3g-WAM wave hindcasts were carried out for the Indian Ocean from 30°E to 120°E and 30°S to 30°N using the analyzed winds of NCMRWF and appropriate open sea boundary inputs. WAM was executed using six hourly input fields over 1.5°×1.5° grid resolution. The outputs of the model such as wave height, peak wave period, mean wave period and mean wave directions were compared with the time-series buoy measurements of National Institute of Ocean Technology (NIOT), Chennai, India and other available measurements. Comparisons between the predicted and observed wave parameters were very encouraging. However, the model predictions of significant wave height were overestimated during the extreme wind and wave conditions. By and large, the WAM predictions were quite reliable for the south-west monsoon (May-September) periods in spite of the limitations. These validation studies have revealed that, the performance of WAM was satisfactory and the hindcast wave fields of WAM for the North Indian Ocean can be utilized for various user applications in the deep waters over 30 meters. © Research India Publications. Source

Swain J.,Naval Physical and Oceanographic Laboratory NPOL | Umesh P.A.,Naval Physical and Oceanographic Laboratory NPOL | Panigrahi J.K.,Nanyang Technological University | Balchand A.N.,Cochin University of Science and Technology
International Journal of Oceans and Oceanography | Year: 2013

During one of the ongoing scientific missions in December 2000 off Paradeep, north-east coast of India various oceanographic and meteorological observations were made from a time-series location beside the selected spatial locations. The measurements off Paradeep revealed that the tidal effect was very prominent in the coastal region with significant changes in the flow pattern, variations in temperature, salinity and sound speed both in space and time. One of the most important features observed during the experiment was the temperature inversion of 1.5 to 4°C which was consistently present throughout the time-series as well as spatial observations. Generally, such inversions are not observed in other parts of the World Oceans. Measured currents clearly indicated the tidal reversals and spatial variations in the flow pattern. The salinity gradually increased from the coast to deep waters (i.e. about 22 PSU to 32 PSU) within a distance of 60 miles. Winds were low varying between 2 to 5 m/s and the predominant wind direction during the observation period was north-east. The sea-state generally remained calm with wave height varying between 0.2 and 0.6m (fair weather season). Tidal influence up to a depth of 50m appeared to be very prominent with its semidiurnal reversal both in magnitude as well as direction. Current speed varied between 0.1 m/s to 0.6 m/s and the predominant direction near to coast was south-west. The inversion layer moved from the surface towards deeper waters during the time-series observations. This might be due to the changes in tidal circulation pattern during the lunar cycle. The measurements during this scientific mission also suggested a salinity front in the upper layers which was extending from the coast up to 40 km offshore. © Research India Publications. Source

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