Acoustic Sources of Opportunity for Ocean Sensing

LT Chris Verlinden
Marine Science Instructor

U.S. Coast Guard Academy

Friday, Apr. 6, 2018, 3:10pm
Chase 130
Abstract

Controlled acoustic sources have typically been used for imaging the ocean. These sources can either be used to locate objects or characterize the ocean environment. The processing involves signal extraction in the presence of ambient noise, with shipping being a major component of the latter. With the advent of the Automatic Identification System (AIS) which provides accurate locations of all large commercial vessels, these major noise sources can be converted from nuisance to beacons or sources of opportunity for the purpose of studying the ocean. The source localization method presented here is similar to traditional matched field processing, but differs in that libraries of data-derived measured replicas are used in place of modeled replicas. In order to account for differing source spectra between library and target vessels, cross-correlation functions are compared instead of comparing acoustic signals directly. The library of measured cross-correlation function replicas is extrapolated using waveguide invariant theory to fill gaps between ship tracks, fully populating the search grid with estimated replicas allowing for continuous tracking. In addition to source localization, two ocean sensing techniques are discussed in this presentation. The feasibility of estimating ocean sound speed and temperature structure, using ship noise across a drifting volumetric array of hydrophones suspended beneath buoys, in a shallow water marine environment is investigated. Using the attenuation of acoustic energy along eigenray paths to invert for ocean properties such as temperature, salinity, and pH is also explored. In each of these cases, the theory is developed, tested using numerical simulations, and validated with data from acoustic field experiments. 

Bio

LT Chris Verlinden is from Portland Oregon. He graduated from the Coast Guard Academy with high honors with a degree in Marine and Environmental Sciences in 2008 whereupon he was stationed aboard the Coast Guard Icebreaker Polar Sea as the Science Officer for two years. Research missions while serving aboard Polar Sea ranged from methane hydrate research to capturing polar bears. In 2010, LT Verlinden transferred to USCGC Sycamore out of Cordova, Alaska where he served as Operations Officer for two years. During this time, LT Verlinden served as task force leader for on scene Coast Guard Assets during the Deepwater Horizon Oil Spill, and as project officer for oil spill response exercises in support of Operation Arctic Shield, earning five arctic service medals in the process. LT Verlinden completed his graduate work at Scripps Institution of Oceanography earning an M.S. in Oceanography in 2014 with research focusing on passive ocean acoustics. In 2014, LT Verlinden began teaching at the U.S. Coast Guard Academy in the Marine Science section, and in 2017 completed his Ph.D. at Scripps Institution of Oceanography with research focusing on passive acoustic source localization and environmental inversion. His research collaborations include extensive work with the Office of Naval Research, Scripps Institution of Oceanography, MIT, Woods Hole, Georgia Tech, Duke, and NOAA. He supervises cadet research in the fields of Geospatial Information Systems, marine mammal physiology and population dynamics, physical oceanography, Coast Guard (CG) Law Enforcement (LE) and Search and Rescue (SAR) mission optimization, and ocean acoustics. LT Verlinden has taught nine different undergraduate courses in Geophysical Fluid Dynamics, Wave Physics, Remote Sensing, Geospatial Information Systems, Atmospheric and Marine Science, Ocean Acoustics, and Geospatial Intelligence. LT Verlinden currently lives in New London, CT where he serves as a Marine Science Instructor at the U.S. Coast Guard Academy.