Matthew Schinault’s PhD Proposal Review

“Development of A Large-Aperture 160-Element Coherent Hydrophone Array System for Instantaneous Wide Area Ocean Acoustic Sensing”

Abstract:

A large aperture coherent hydrophone towed array system comprising of 160 elements and an aperture length of 192 meters has been developed for real-time instantaneous wide-area ocean acoustic remote sensing and monitoring. The design and manufacture of these arrays requires a multidisciplinary approach to achieve acoustic performance capable for detection, classification, localization and tracking. Drawing from disciplines such as material science, electrical engineering, mechanical engineering, hydrodynamics, oceanography, bioacoustics and signal processing. Due to the cost and complexity of towed array technology, development of large aperture towed arrays has been limited at the university level. With military, oil and gas exploration as the chief technology developers and users. The military and commercial focus is narrow and does not allow for scientific study, resulting in significant gaps in the way we understand ocean acoustics around the globe. Here we model, design, fabricate and field test a broadband array for general ocean sensing that is configured to support a wide range of research to include study of marine mammals, fish shoals, geophysical processes, surface or subsea man-made craft, seismic surveying and the various challenges associated with detection, classification and localization of underwater sound sources.

Here, we present the design process, beginning with modeling and measurement of piezoelectric material properties. This allows us to perform finite element analysis, estimating beampatterns and frequency response with a hydrophone electrical model. A pressure to voltage input model of the hydrophone is used to obtain the voltage levels produced to then configure amplification, gain and filter stages providing a system level transfer function from analog to digital conversion. The array performance with a delay and sum beamformer is estimated for a broad range of frequencies, with beamforming above half-lambda spacing. The components of the mechanical tow package are modeled to inform array construction estimating vibration and flow noise. A turbulent boundary layer model for flow noise estimation and environmental noise model determines the gains and cutoff frequencies necessary for performance. The comprehensive performance model is compared with a parameter estimation from test data to quantify array performance.

Towed arrays are subject to environmental extremes, with time at sea being costly. To increase the reliability, the array is designed using field replaceable pressure tolerant components including hydrophones, pre-amplifiers, power modules, telemetry and analog to digital conversion units. All components are verified by pressure chamber testing to ensure operation at depth. This large aperture array was able to be made without specialized facilities by utilizing modular interchangeable array interconnects allowing for conventional array populating and oil-filling methods with aperture lengths that are serviceable onboard research vessels. Array design, fabrication and assembly was performed on-site at Northeastern University in Boston, Massachusetts. Examples of passive acoustic data from array deployment during a sea trial in the U.S. Northeast coast are presented illustrating array capabilities.

Committee:

Prof. Purnima Ratilal Makris (Advisor)
Prof. Marvin Onabajo
Prof. Yongmin Liu
Dr. Alessandra Tesei