M Sc Thesis on underwater noise in coastal areas

About the master thesis
Background
Life in our coastal regions are under large environmental pressure from many human activities, one of which is underwater noise from recreational boating. To better understand the impact from recreational boats, the underwater noise has been measured in two regions of high traffic intensity, Vasholmarna on the west coast and Trosa skärgård on the east coast. The underwater noise was measured on both sites during several weeks, and the movements of boats in the area were tracked manually during one day. On each site, multiple recorders were placed in select locations of different characters, e.g., sheltered shallows, or open deep water.

The project
The core of the project is to determine the contributions of recreational boats to the underwater soundscape in coastal areas.

This should be estimated by comparing the noise data recorded at different locations using time-frequency representations of the recorded signals and statistical metrics, e.g., various percentiles. These metrics should be compared and related to the character of each location. It will also be important to compare noise data inside a 5 kn speed reduction area to noise data recorded in an adjacent area where there are no speed restrictions.

The project additionally has multiple possible avenues to pursue depending on the interest and skill set of the applicant(s).

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How can recreational boats be detected from underwater noise data? Commercial ships have AIS transmitters that broadcast their position at regular intervals, and this can be used to determine when they are near a recording station. Some recreational boat owners choose to get an AIS transmitter for their boat, but most do not. There is therefore no simple way to determine recreational boat presence. The task here is to develop a detection algorithm that uses only recorded underwater noise data. This can be used for separating the noise levels into natural noise and anthropogenic noise, which gives a convenient metric that can be used to measure impact. This metric would be compared to a metric based on statistical analysis of the noise data using percentiles.

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What would be the effect of introducing a speed reduction in a given area? One potential avenue to mitigate recreational boat underwater noise is to introduce a speed limit on boats in an area. Except for comparing in situ recorded data as proposed in the first item, there are no readily available tools to evaluate the efficacy of such scenarios. The goal for this part would be to develop a method to modify recorded signals based on known movements of boats, a new target speed, and a known speed induced reduction in noise power.

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How does underwater sound propagate in shallow, coastal regions? Widely used propagation loss models for underwater acoustics are designed for long distances and deep waters, and therefore will not work or will be too demanding to use in coastal areas. This work would focus on developing an empirical model for underwater sound propagation in shallow, coastal regions. The data available to do this consists of controlled movements of a boat in the Vasholmarna area. Additional data collection can be made during the project using either a boat source or an underwater speaker. The core question is what type of model to use, and how to fit the chosen model to the measured data.

Qualifications
- General programming. The project algorithms should be written in python, and incorporated within an existing tool set.
- Understanding of time-frequency representation of acoustic signals.
- Signal processing, statistics or acoustic propagation models, depending on the track.

Group size: one or two students.

Place: Gothenburg

Start date: Jan 8, 2024.

Credits: 30

IVL and our work on underwater noise
IVL Swedish Environmental Research Institute is an independent, non-profit research institute that employs 440 people. We work very broadly within the field of sustainable development, and undertake both research projects and expert consultancy.

Underwater noise is a growing topic and currently we are five researchers in acoustics, signal processing and marine biology.

The proposed master's thesis project(s) will be connected to a Formas funded research project that aims to estimate the pressure of motor boat underwater noise on coastal regions and predict the effect of the current trends of an increased traffic and increased engine sizes.

The project has developed a speed dependent source model for motor boats, which will be used to simulate the noise emissions depending on the speed.

Contact
For questions, please contact:

Torbjörn Johansson

[email protected]

010-788 6702