Ocean wave seismic and acoustic noise detected with distributed fiber optic sensor array

The U.S. Army Engineer Research & Development Center installed a Fiber Optic Sensor System (FOSS) at the Field Research Facility (FRF) in Duck, NC as a test-bed for evaluating FOSS performance in measuring ambient acoustic and seismic noise in a coastal environment. The sensor system consists of a buried fiber optic cable with a length of approximately 3 km, which wends its way through the sand dunes and along the beach. An optical interrogator contains a pulsed laser which injects light into an optical fiber within the cable and receives Rayleigh backscattered signals from it. The system, which is able to detect and locate seismic activity along the entire length with a 10 m resolution, is being used to study ocean wave generated noise. The FRF also maintains and operates a real-time cross-shore directional wave array, consisting of five bottom-mounted acoustic wave gauges installed at 2 to 11 m depths. The main focus of the work presented here compares FOSS data with directional wave measurements made with the cross-shore array under a variety of conditions. Data collected with other sensor systems (e.g., vertical long-period seismometer, infrasound microphone, anemometers, rain gauges, high resolution video) were also used in this comparison.