Low Frequency Ocean Acoustic Phenomena (LOWFOAP)

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 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 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 a source of interference and/or a source of opportunity. Current understanding of these mechanisms is very limited for noise below 100 Hz and ocean acoustic phenomena below 10 Hz are rarely studied and even less well understood.

There is a clear need to identify these 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 is supported by iCASE co-funder DSTL Acoustics and AWE Forensic Seismology. Placements at both will provide the student with unique access to defence and security expertise from both supervisors and the benefits of establishing links with different research communities. The student will spend at least one month per year visiting DSTL (amounting to 3+ months over the course of the PhD) to gain experience of defence research activity in underwater acoustics. This will be supplemented with a period of at least three months visiting AWE in the second year to work directly with AWE experts. AWE will provide unclassified data from the International Monitoring System (IMS) network of stations to the student for analysis. The total placement time of 6+ months, strategically timetabled throughout the progression of the PhD and aligning with project objectives, will provide the student with new skills and a unique perspective on acoustics research problems and their applications.