Low Frequency Ocean Acoustic Phenomena (LOWFOAP) at University of Bath
Posted on Apr 2, 2019 in Job Opportunities in Acoustics
Sounds dominate the oceans, spanning all frequencies and coming from different sources: natural (e.g. wind, rain), biological (e.g. marine mammals, fish) and anthropogenic (e.g. ships, seismic exploration). Very-low frequency hydroacoustic signals (< 100 Hz) are often associated with geophysical processes, like earthquakes and landslides, but they can be linked to man-made activities, like offshore industry, fish blasting, or even nuclear test explosions. Understanding the mechanisms generating noise below 100 Hz, has important applications for monitoring nuclear explosions (for example, the combined use of seismic, hydroacoustic and infrasound signals to detect and study distant phenomena, particularly explosions, but also submarine accidents or aircraft impacts), and to naval operations such as anti-submarine warfare, where noise can be either or both a source of interference and a source of opportunity. Current understanding of these mechanisms is very limited for noise below 100 Hz. The ocean acoustic phenomena below 10 Hz are rarely studied and even less well understood, which betrays the technical challenges associated with this frequency regime, despite the importance to defence and security.
Remote sensing, for explosion monitoring, naval sonar (detection, classification and localisation) and other areas of acoustical oceanography, needs to identify these distant phenomena (from any location), characterise each event (natural or artificial), estimate the propagation of the event through the ocean acoustic environment, and locate it accurately (latitude, longitude and depth). This is made more difficult by often significant broadband background noise, over and above the fundamental thermal noise in the ocean, and complex acoustic propagation through the Earth, in the ocean and at the interfaces between ground and water, and water and air. This project aims to:
1. Investigate the acoustic variability of key candidate mechanisms (geological disturbances, melting of marine ice and polar glaciers, wind, distant storms, breaking waves, rain, marine mammals, shipping, surveying, sonar, and many others);
2. Spanning extreme spatial and temporal variability, the low-frequency components of these mechanisms are subject to unusual propagation in the ocean environment, which can include coupling with one or more sediment layers, generating seismic and interface waves, and coupling with the ocean surface and between the ocean and the atmosphere;
3. Develop operational models to calculate the variability and propagation in a range of different environments, to be used in different contexts of explosion monitoring and naval sonar.
The project will provide unique insights into both the characteristics of the low frequency, very low frequency, and ultra-low frequency ocean acoustic noise spectrum and the way that this noise propagates through the ocean acoustic environment, and how it interacts with surfaces and structures in the environment, across this mammoth frequency range.
This project will take place at the University of Bath, in a research group at the forefront of underwater acoustics and with a track record of successful students. The student will also work closely with DSTL (industrial supervisor / co-supervisor) and the Forensic Seismology team of AWE. It is expected that the applicant will spend at least 1 month per year at DSTL, and do a 3-month placement in Year 2 at AWE. The total placement time of 6+ months, strategically timetabled throughout the PhD and aligning with project objectives, will provide the student with new skills and a unique perspective on acoustics research and applications across three different communities (Bath: academic, DSTL: defence, AWE: defence/industry).