NOPR Collection: Special Issue on Technologies for Ocean Exploration (Guest Editors: CVK Prasad Rao & C. Revichandran)

Sources of errors in the measurements of underwater profiling radiometer

2014-01-01T00:00:00Z

Title: Sources of errors in the measurements of underwater profiling radiometer Authors: Silveira, Noah; Suresh, T.; Talaulikar, Madhubala; Desa, Elgar; Matondkar, S.G. Prabhu; Lotlikar, Aneesh Abstract: There are various sources of errors from the measurements of optical parameters using a radiometer, which can be classified as mode of deployment, instrument and environment. The errors from the deployment are primarily from the ship and superstructure shadows. Instrument could be a source of error arising from its self-shadow, drift in the calibration and temperature effects. There could be large errors, which at times may be unavoidable to environment factors such as wave focusing at the surface layers, sea state conditions which may affect the tilt of the instrument, atmospheric conditions such as cloud cover, solar elevation, wind and rain. Radiometric optical data in water could also get affected due to Raman scattering and fluorescence effects. Here we discuss the above sources of errors and how they could be minimized. From the measurements carried out in the coastal waters off Goa and Arabian Sea using the hypespectral radiometer, we propose simple protocol to measure the data and also screen the erroneous data measured from the radiometer. Page(s): 88-95

Real Time wave forecasting using artificial neural network with varying input parameter

2014-01-01T00:00:00Z

Title: Real Time wave forecasting using artificial neural network with varying input parameter Authors: Vimala, J.; Latha, G.; Venkatesan, R. Abstract: Prediction of significant wave heights (Hs) is of immense importance in ocean and coastal engineering applications. The aim of this study is to predict significant wave height values at buoy locations with the lead time of 3,6,12 and 24 hours using past observations of wind and wave parameters applying Artificial Neural Network. Although there exists a number of wave height estimation models, they do not consider all causative factors without any approximation and consequently their results are more or less a general approximation of the overall dynamic behaviour. Since soft computing techniques are totally data driven, based on the duration of the data availability they can be used for prediction. In the National data buoy program of National institute of Ocean Technology, not all the buoys have wind sensors and wave sensors and so it is attempted to apply neural network algorithms for prediction of wave heights using wind speed only as the input and then using only wave height as the input. The measurement made by the data buoy at DS3 location in Bay of Bengal (12^o11’21"N and 90^o43’33"E) are considered, for the period 2003-2004. Out of this, the data of period Jan 2003-Dec 2003 was used for training and the data for the period July 2004- Nov 2004 is used for testing. Real time wave forecasting for 3,6,12 and 24 hours were carried out for a month at the location chosen and the results show that the ANN technique proves encouraging for wave forecasting. Performance of ANN for varying inputs have been analysed and the results are discussed. Page(s): 82-87

Prospects for developing a minor port facility at Betul, Goa

2014-01-01T00:00:00Z

Title: Prospects for developing a minor port facility at Betul, Goa Authors: Mathai, Thomas; Kumar, Satish; Rajarama, K. N.; Kumar, P. Praveen; Chandran, M. Suresh Abstract: Marine and Coastal Surveys Division of Geological Survey of India, initiated preliminary, integrated geological, geotechnical and geophysical surveys off Betul for making an appraisal of the developmental possibilities of setting up a minor port in this sector. Detailed surveys helped generate a bathymetric map of the area indicating a smooth and gently sloping seafloor without any hazards, ideal for port development. Sediment cores were studied to evaluate the sub-seabed sediment package and visualize the seabed sediment distribution. Mean size of the seabed surface sediments broadly signifies a sediment milieu encompassing variants from silt to clay, broadly classified as silty clay. Geotechnical analysis of the sediments helped to evaluate the engineering properties of the seabed and sub-seabed sediments quintessential for development of a port in this sector. Clayey sediments have a high degree of plasticity with a very high swelling potential. Shear resistance is almost unregistered at almost all levels of the sediment package. Geotechnical characteristics of the sediments are generally conducive for offshore structures. Side scan sonar surveys brought out a clear seafloor, generally monotonous and thus well suited for a navigational channel access. Current Observations carried out in the nearshore sector indicate low velocity currents and are not influenced by tidal variations. Environmental parameters including Temperature, pH, Salinity, Conductivity and Dissolved Oxygen were studied to record the conditions prevalent in this sector, for post-development comparison. Page(s): 76-81

Oscillating environmental responses of the eastern Arabian Sea

2014-01-01T00:00:00Z

Title: Oscillating environmental responses of the eastern Arabian Sea Authors: Gerson, Vijay John; Madhu, N V; Jyothibabu, R; Balachandran, K K; Nair, Maheswari; Revichandran, C Abstract: Characteristics of two distinct physical processes, the coastal upwelling and convective overturning, which enhance phytoplankton productivity in the west coast of India, are discussed in this study. Systematic in-situ data collected during the two contrasting monsoon (summer and winter) periods were utilized for the study. During summer monsoon, the colder (27°C), less oxygenated (<190 μM), nitrate rich (NO₃-N >2 μM) waters were evidenced in the upper layers of the southwest coast of India, along with higher level of primary production (surface - 76 mgC m^-3d^-1 & column -1629 mgC m^-2d^-1) and chlorophyll a (surface - 1.2 mgm^-3 & column -45.7 mgm^-2). In contrast, during winter, the upper thermohaline layer of the northeastern Arabian Sea exhibited colder sea surface temperature (SST, 25-26°C), and deeper mixed layer depth (MLD, >70 m). This area was distinguished by less oxygenated (<180 μM), nitrate rich (>2μM) and high productive (surface - >10 mgC m^-3d^-1 & column - >800 mgC m^-2 d^-1) waters. I can be stated that the physically forced chemical changes occurred in the upper layers of both southeastern and northeastern Arabian Sea, appeared in an oscillating manner with respect to monsoonal changes, seemed to trigger the enhancement of phytoplankton productivity of the area. Page(s): 67-75