Review to 3D mapping of Low frequency ambient shipping noise

Overview

The Indian Ocean Region has deep roots in overseas trade routes and several vessels finding their way through it, making it one of the most important sea areas today. As a result, it has also given rise to the Low frequency shipping noise radiated from the vessels (ships) passing through it. This article states the different models that have been developed so far, which enable us to develop a complete three-dimensional version of Underwater Low Frequency Shipping Noise propagation in conjunction with other recording platforms such as hydrophones, using parameters like bathymetry, sound speed, sedimentation, and a culmination of all these.

The research note below enlists all the methods discovered so far with their pros and cons inclusive. The idea of underwater sound propagation mapping dates to World War – I till the advent of SONAR for underwater communication and an emerging source for pollution making the disastrous survival of mammals inside. The note here not only encapsulates the various ways to estimate but also provides an insight to the future scopes for enhancement of further research in varied dialects.

Key highlights

● The primary objective of this research note is study of various techniques modeled so far developing the complete bookmark to three-dimensional version of the sound mapping propagating underwater

● The research note gives an insight to merits and demerits of each adapted model along with a sample outcome attached for a better understanding of the readers.

● However, throughout the course of this study, all reference files and documentations used and needed are linked in the end in order to facilitate the replication of such models for further use in future research.

● Sound propagation noise mapping of an area displays the varying noise levels in a region in the form of a color-coded map, also called heatmap, in accordance with several parameters like bathymetry, temperature, sedimentation and seamounts with microphones like hydrophones.

● A 3D – mapping of noise underwater can be a source point to further research and studies in various domains and a crucial step in moving towards expanding the understanding of the Underwater Domain.

● One of the best benefits of 3D mapping is that it provides the latest technical methods for visualization and gathering information.

● Underwater Noise is measured through hydrophones which are the underwater equivalent of a microphone which measures the sound in the region by factoring the pressure changes in the surrounding.

Key Applications

● As an outcome to the project, we will be working on developing a complete software package that displays 3D-modeling of variation in Shipping Noise levels in a region as we move along the surface (Lat-Long) on IOR

● Factorize the variations observed with depth under the sea level along with ambient noise mapping in the region under IOR (Indian Ocean Region)

● Performing detailed analysis over around 11 oceanic water layers for low frequency ambient noise radiated to get the desired outcome

● Review and application of chosen dataset based upon the AIS (Automatic Identification System) in 2D modeling following with the 3D modeling

Key Challenges

● Best model available: Beginning with the application of Kraken model to PyRam model using parabolic equations, Normal mode, and Ray – beam tracing finding the best possible method and implement it with the present available in conjunction with AIS data collected.

● Vulnerability of AIS Data: The original purpose of AIS was to provide for safety, and not for security purposes.

● Only Shipping Noise through AIS: Making a model of variation of Noise levels in the ocean considering the shipping noise as its only source, while has its own applications and reasons, must not be considered as a reference for noise levels in the oceans.

● Resolution of Data and Processing Limitation: The procedure of collecting and storing of AIS data to be used for simulations requires many sub-steps to calculate the noise levels in a region.

● Lack of proper dumping sites poses a big problem in sediment disposal.

● Other aspects which need to be addressed range from Policy issues to technology gap and capacity & capability building requirement.

● There has been a lack of understanding of underwater medium due to random behaviour and underwater channel fluctuations.

Future Aspects

● Three-dimensional mapping of underwater sound acoustics can be used for scientific studies such as to study the phenomena of noise behavior underwater. Studying and reducing the transmission losses by understanding the conditions that persist in that region. The temperature variations, bathymetry, salinity etc.

● Uncertainties always remained about the multi-path propagation of sound underwater, small bandwidth were available, serious signal attenuation over large distances and time variations of the channel can now be made easier with 3D-mapping into the picture.

● Another thing which is to overcome in future for successful implementation of three-dimensional acoustics is monitoring the environment, as pollution of the ocean waters has increased in both quantity and frequency of occurrence. Because our scope of coverage area in the oceanic arena increases, there will also be an increase in environmental conditions playing an inevitable determining factor.

● High pressure of air and water combined, unpredictable events, and unknown subsea areas. Underwater acoustic networks have applications in exploring the unknown regions in the ocean which majorly comes under the future applications of 3D – Shipping sound mapping propagating underwater.

"Three-dimensional mapping of underwater sound acoustics can be used for scientific studies such as to study the phenomena of noise behavior underwater. Studying and reducing the transmission losses by understanding the conditions that persist in that region. The temperature variations, bathymetry, salinity etc."

1280 853 Maritime Research Center

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