Sea Technology

JUN 2017

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28 st / June 2017 signals encounter fewer suspended particles as they pass through the water column and, thus, are not as subject to scattering, absorption or reflection. As a result, low-frequency signals are able to travel farther without significant loss of signal strength. Chebyshev Polynomial Chebyshev transform was done on the sound slowness squared and the resulting spectrum plotted. For the acoustic signal, we used short-time Fourier transform processing and time- frequency analysis. It was found that the first two order modes of the sound signals received in four sound speed profiles have the most energy. Also, the first order has more energy than the second order, so they have the most influence on the signal waveform. As a result, the first two order modes have a large effect on the correlation of signal waveforms. Group Speed We also measured the group speed by making a correlation between the signals received in the sand at two points. The maximum value of our correlation function gives the time of arrival of the signal, from which the group speed can be calculated. Conclusion The model we developed was test- ed to predict sediment transport in a shallow-water region, at a depth less than 50 m, where two ancient sub- merged cities are located in the Bay of Bengal. The normal mode model generated revealed the behavior of the acoustic pressure signal at particular locations based on depth and speed, as well as group speed and amplitude of the acoustic signals. The resonance of these signals indicated where the sediments linked to the artifacts were deposited, thus giving marine archeol- ogists an indication of where to search. Our model resulted in the discov- ery at 20-m depth of artifacts that had migrated through sediment movement. These national treasures showcase In- dia's rich history. References For a list of references, contact Dr. Sakthivel Murugan at sakthivels@ssn. ST Harshitha Duraisamy completed her undergradu- ate degree in electronics and instrumentation en- gineering at Adhiyamaan College of Engineering, Hosur, India, in 2015 and is currently pursuing her master's in applied electronics at SSN College of Engineering, Chennai. She is involved in projects related to geoacoustic inversion, acoustic propaga- tion models for the study of sediments and under- water noise modeling. G. Annalakshmi completed her undergraduate de- gree in electronics and communication engineer- ing at P.B. College of Engineering, Chennai, India, in 2011 and her postgraduate degree at the Anand Institute of Higher Technology in Anna University, Chennai, in 2014. She is now pursuing her doctor- ate at SSN College of Engineering, Chennai. Her research interest is in the field of underwater com- munication, low-power VLSI and signal processing. Dr. S. Sakthivel Murugan is an associate professor at SSN College of Engineering, Chennai. He has more than 15 years of experience in academia and research. His areas of research are underwater acoustic signal processing and underwater sensor networks. He has an underwater acoustic research lab at SSN. Mode number versus group speed. UNDERWATER LISTENING SYSTEMS Versatile Acoustic Recorders Real-Time Listening Remote Buoys New Noise Processing Features 25 rue Michel Marion 56850 Caudan - France +33 (0)297 898 580 - International Standard and Guideline Compliant (ANSI, MSFD...)

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