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

Abstract

A large aperture coherent hydrophone array system comprising of 160 elements has been developed for real-time instantaneous wide-area ocean acoustic remote sensing and monitoring. The overall acoustic aperture length is 192 m with array elements nested into four sub-apertures each with 64 hydrophones and spacing corresponding to half-wavelength at design frequencies of 250 Hz, 500 Hz, 1000 Hz and 2000 Hz. Hydrophones with integrated broadband pre-amplifiers designed with a linear frequency response from 10 Hz to 50 kHz send differential pair amplified and filtered analog signals to multiple 24-bit, 32-channel Analog to Digital Converters (ADC) with sampling rate that is programmable up to 100 kHz per channel. Array internals are designed using field replaceable pressure tolerant components including hydrophones, pre-amplifiers, power modules, telemetry and ADC units verified by pressure chamber testing. Forward and aft modules are equipped with non-acoustic sensor elements to provide depth, heading, pitch, roll and temperature measurements. Acoustic aperture telemetry is User Datagram Protocol (UDP) converted to Single-Mode Fiber for transmission along 600 m of faired tow cable to a shipboard acquisition system. The data acquisition system is designed for continuous data-flow to enable real-time processing with fiber-optic tow cable and Gigabit Ethernet components. Array design, fabrication and assembly was performed on-site at Northeastern University in Boston, Massachusetts. 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. Examples of passive acoustic data from array deployment during a sea trial in the US Northeast coast are presented illustrating array capabilities.