Bottom-mounted Fiber Optic Sensing of Nearshore Hydrodynamics
Abstract
Recognizing the explosive growth of the nascent field of Distributed Acoustic Sensing (DAS) using optical fibers as sensors in the m arine environment, this project will apply the DAS measurement technique to the observation and characterization of the coast shore. I will use DAS signal in order to measure bottom disturbance from a range of hydrodynamic signals including gravity waves, in fragravity waves, sneaker waves, meteotsunami, internal waves, river fronts, and potentially tsunami. DAS measures longitudinal stra in through optical interferometry of a sequence of short laser pulses injected into one end of a standard single-mode optical fiber. DAS can measure strain over distances up to 150 km with spatial resolution as low as 1 m, and resolving fiber strain as small as 10 0 nanometer length change over 10 m of fiber. The advantage of DAS is continuous temporal sampling over long spatial distances; DAS can provide 1000s of measurements along its cable length, where current in-situ sensing techniques are limited to at most 10s of sen sors. In the coastal ocean, the propagation and generation of low frequency hydrodynamic signals are largely under characterized alo ng long spatial scales, long range DAS sensing will allow for spatial resolution of these signals from the inner shelf to the nearsh ore. The Scientific and Technical Goals of the proposed effort are to: 1) quantify the capability of DAS for nearshore sensing by gr ound truthing its measurements with trusted and legacy data streams and develop new algorithms for detecting coastal hydrodynamic si gnals,2) create transfer functions for strain (DAS measurement) to dynamic pressure and to bottom stress (usable quantities in coast al oceanography), and3) spatially and temporally correlate the propagation of hydrodynamic signals evolving across the coastal zone on the seabed (measured by DAS) and on the sea-surface (measured by radar, camera, and eventually satellite). DAS paired with remote sensing will extend spatial correlations from seabed to sea-surface. The proposed work will sample on two ocean cables that are loc ated in distinctly different coastal environments. The first deployment will be on a fiber run through the cross shore at the USACE Field Research Facility (FRF) in Duck, North Carolina. Duck, NC is frequently impacted by hurricanes, which causes large swell and s urge events, and it is apt to be influenced by meteotsunami. Additionally, the FRF has a long-term and continuous field array measur ing waves and currents in-situ and remotely that can be leveraged for ground-truthing DAS signal. The second deployment will be on t he existing 20 km long Oregon State University PacWave fiber used for wave energy research located off of Newport, Oregon. The Newpo rt, OR cable is located near the mouth of the Yaquina River and runs to depths of 150 m, the region is frequently influenced by high energy gravity waves, sneaker waves, internal waves, and river fronts. In Newport we deploy in-situ instrumentation to measure wave s and currents as well as a shore-based XBand radar station to image nearshore hydrodynamics overlapping with the bottom-mounted fib er. DAS could be relevant to many U.S. Navy applications, from environmental monitoring to hazard detection. In the proposed effort U.S. Navy relevant applications include support sensing of environmental hydrodynamic signatures and their transformations over spac e and time, development of sensing algorithms for extreme hydrodynamic events, and continuity of connecting high-resolution bottom m easurements from DAS with remote sensing surface measurements from camera and radar.Approved for Public Release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 20, 2021
- Source ID
- N000142112676
Entities
People
- Meagan Wengrove
Organizations
- Office of Naval Research
- Oregon State University
- United States Navy