Overview
This paper states that the standard modes of signal transmission underwater are acoustic waves and a large majority of marine life uses sound waves for regular movement. Therefore, the classification and analysis of sources of underwater noise becomes imperative. The study classifies the noise in context of ships into following types: (1) Underwater radiated noise, (2) Noise onboard the ship and (3) Self Noise. Of these, the most important classification, which will also be the subject of this report’s discussion, is underwater radiated noise. This report mainly focuses on noise generated by human shipping activities.
This research note aims to present a high-level view on the sources of noise underwater, and then focuses on Underwater Radiated Noise (from human shipping activities). It further presents various existing models for its estimation. The research note suggests that the first step towards dealing with noise is to estimate its sources and level.
Key highlights
- Noise is described as the unwanted sound that interferes with the normal functioning of a system. Noise in the ocean is the result of both natural and anthropogenic sources.
- Natural sources of noise include processes such as earthquakes, wind-driven waves, rainfall, bio-acoustic sound generation and thermal agitation of the seawater.
- Anthropogenic sources include shipping, oil and gas exploration, naval operations, fishing etc.
- Additional factors such as machinery noise, vibrations in the hull and flow noise also contribute to the radiated noise level of the ship.
- Some of the existing models that estimate radiated noise levels based on various parameters of the ships are- The Ross Model, the RANDI Model, The Wales-Heitmeier Model and the Wittekind Model.
- Details on each of the above-mentioned models have been elaborated in the research paper, kindly refer to the paper for further individual details.
- The input parameters to the various models described above can be obtained from the AIS data of the ship.
- This report suggests that AIS can be used for many different functions such as for maritime security, fishing fleet monitoring and control, aids to navigation, oil spill monitoring, ocean currents estimates and ocean ambient noise mapping
Key recommendations
- It is imperative to optimise models taking into account particular vessel type in the Indian Ocean Region. A study can be done on the types of ships present in the Indian Ocean Region (which is a tropical littoral region), and the Wittekind model can be tuned accordingly to give the most accurate results possible for ships in the IOR.
- It is important to obtain parameters for the Wittekind Model from AIS data. Since all the parameters required for the Wittekind model are not easily available, therefore, the knowledge of naval architecture can be used to derive these unavailable parameters from the available AIS data.
- There is a need to devise accurate models for radiated noise generation. As all the current estimation models only use a handful of ship parameters as inputs, therefore, there is a need to increase the number of ship parameters and the oceanographic conditions should be increased while devising noise models.
“The first step towards dealing with noise is to estimate its sources and level. While most direct methods of measurement of radiated noise are rather expensive, a variety of simulation models exist which estimate the level based on a variety of inputs from a number of sources (such as AIS data).”
