NSFGEO-NERC: Collaborative Research: Direct comparison of ocean temperature and velocity structure from in-situ measurements and distributed optical fiber sensing

This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget.

Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries.

This is a project to be carried out jointly between the United States and the United Kingdom. It seeks to implement a new measurement technique called Distributed Acoustic Sensing. The technique would provide images of water temperature and current velocity fields in a cross-section delineated by an existing telecommunication and power cable laid on the sea floor off one of the Azores islands.

Images would be generated with unprecedented resolution (10 m in space, minutes in time) through the development of a ‘noise interferometry’ technique as part of the Distributed Acoustic Sensing. The technique measures the cable stretching caused by pressure changes and how such cable stretching varies over time. The noise interferometry values will be compared to measurements from conventional oceanographic moorings and ocean bottom seismometers.

The study will assess the noise interferometry method in several ways: quantify its skill; demonstrate its robustness to uncertainties; determine its feasibility to depict turbulence properties; and apply it to research on internal tidal fluxes around the island of Madeira. As Broader Impacts, the project will provide information with spatial and temporal resolutions that should allow improvements in the skill of climate model projections.

Also, the project will strengthen a collaboration with the UK while providing training for four Naval Postgraduate School graduate students and two undergraduate interns at University of California San Diego.

This is a joint US-NSF/UK-NERC proposal to obtain high resolution (10 m in space, minutes in time) distributions of temperature (sound speed) and velocity fields above a 34-km cable laid on the seabed off Madeira Island. Distributions will be drawn by developing a noise interferometry technique, which combines acoustic and gravity wave noise interferometry methods through Distributed Acoustic Sensing.

The approach measures strain and strain rate values throughout an existing telecommunication and power cable on the ocean’s bed. The noise interferometry values will be compared to measurements from conventional oceanographic moorings and ocean bottom seismometers. The study will assess the noise interferometry method in several ways: quantify its skill; demonstrate its robustness to uncertainties and variations in mechanical coupling between cables and the seabed; determine its feasibility to depict turbulent dissipation rates; and applying it to research on internal tidal fluxes interacting with the island of Madeira, and associated tidally-driven turbulence in the bottom boundary layer over the topographic slope.

Results will be analyzed in the context of internal wave interactions and of bottom boundary layer properties. In terms of Broader Impacts, the project will provide information with spatial and temporal resolutions that should allow improvements in the skill of climate model projections. Also, the project will strengthen a collaboration with the UK while providing training for four Naval Postgraduate School graduate students and two undergraduate interns at University of California San Diego.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.