Using distributed acoustic sensing to monitor Galway bay’s ocean noise

The global ocean environment consists of various complex mechanisms whose better understanding is crucial to study topics such as climate change and the interactions between the ocean bottom and solid Earth. The emergent technology of Distributed Acoustic Sensing (DAS) is presenting itself as a significant tool to help overcome some of these barriers. DAS utilises the optical phase difference of Rayleigh backscattered light from within an optical fibre to measure the dynamic strain of the fibre in response to mechanical signals interacting with it, producing a spatially dense dataset of strain-meters, known as channels. Within this thesis, an optical fibre connected to the Galway SmartBay, Galway, Ireland, an offshore observatory hosting multiple ocean environment sensors, was interrogated for two acquisitions. The spatial density of DAS provides more information which can be utilised to better understand the oceanographic wavefield behaviour in the Galway Bay area. This included characterising the impacts of the tides, swells generated from distant storms and ocean currents on the wavefield, providing another source of information for climate and coastal hazard monitoring. Following this, the presence of a local secondary microseisms and ambient high frequency Scholte waves was identified and studied. These wavefields were observed to correlate temporally as well as with local weather conditions, indicating the presence of a potential coupling mechanism between the atmosphere, sea surface, and solid Earth. This highlights the feasibility of near-shore case studies on this coupling mechanism, as well as the opportunity to use DAS to further study ocean processes and their implications on the seismic wavefield in Galway Bay. Lastly, some applications of DAS were explored, including the earthquake detection and acoustic signal tracking capabilities of the fibre. These show great potential for incorporation of DAS measurements within offshore facilities, such as the Galway SmartBay.

Funder

Geological Survey of Ireland

Publisher

University of Galway

Rights

CC BY-NC-ND

cbn

Collections

University of Galway Theses (Research Masters Theses)