Sea Technology

JUN 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 26 of 72

26 st / June 2017 T he underwater ocean environment is the new frontier for discovery. In order for researchers to explore its vast re- sources, new methods are needed, for instance, in the area of optical and acoustic underwater communication. In India, we seek to mine our rich heritage, much of which lies underwater. Many artifacts become further bur- ied due to sediment transport. We've developed a model for predicting sediment transport following the inversion meth- od, which includes analysis of sea characteristics and types of sediment and foundation. Geoacoustic inversion helped us to develop the prediction model by inferring nonlinearity in signal due to various sources. The Bayesian model was initially used to discriminate between various types of sedi- ment. With our model, the impacts of sediment transport over time can be predicted. Purpose This work was carried out with an intention to find arti- facts from the ancient cities of Puhar (Poompuhar) and Ma- habalipuram, now submerged underwater. Puhar, along the shore of the Bay of Bengal, was a flourishing port city of the early Chola kingdom that was repeatedly afflicted by floods and erosions. Excavations of submerged wharves and pier walls extending out several meters in length have confirmed the ancient literary sources that refer to this town. Marine archaeologists have recovered pottery dating back to the fourth century B.C. To pave the way for finding more artifacts lying in shal- low water (less than 50-m depth), we tested the theory that the acoustic vector field contains information that could be used to invert for the geoacoustic properties of the seafloor. Integral acoustic properties of the sea bottom are deter- mined by a geoacoustic inversion model. Inversion using modal wave numbers was used to deter- mine compressional sound speed as a function of depth in the seabed. This approach better approximates the layered structure of the sediment. Spatial variability is examined by mapping results obtained by multiple independent local inversions. This is achieved by estimating geoacoustic parameters, where parameters are synthetic data used in a perturbative Model Predicting Sediment Transport Acoustic Analysis Aids Research on India's National Treasures By Harshitha Duraisamy • G. Annalakshmi • Dr. S. Sakthivel Murugan (Top and Bottom) The wave number is the number of waves crossing a unit area. Wave number decreases with increased modes. Amplitude of the first four modes varies with increas- ing depth. inversion algorithm employing qualitative regularization. The advantages of using qualitative regularization are that it handles issues of stability and uniqueness well and it provides a mechanism for resolving the layered structure of the seabed.

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