Acoustic Communications Measurement Systems (ACOMMS)

Agency/Department

FLC Region

Security Lab

No

Address

4555 Overlook Avenue S.W.
Washington

(P)

202-767-3083

Description

FUNCTION: Design and develop adaptive signal processing techniques to improve underwater acoustic communications and networking. Phase coherent and incoherent signal patterns are transmitted from NRL's acoustic projector source systems through the underwater medium to NRL's receiver systems. Improved signal processing techniques are developed and refined to minimize the bit error rate and to evaluate environmental influences on the processor's performance.

DESCRIPTION: Our acoustic communications research systems enable our team to conduct experiments at frequencies from 3 to 60 kHz. Source signal patterns are designed by NRL, transmitted into the ocean medium, and received at distances out to 15 km. The received signals are processed in situ and recorded for post-experiment data processing. Acoustic Communications Data Storage (ACDS) buoy systems transmit at source levels up to 185 dB. For higher sound pressure levels, an acoustic projector mounted in our 4-ft V-fin towbody develops up to 200 dB. ACDS buoy systems include 8-element vertical line arrays with variable apertures.Our shipboard-based vertical array has a wide aperture of 16 elements and is deployed from a vessel at anchor. Relative position, speed, and depth of our projectors and receiver arrays are carefully controlled throughout the experiments. Impact of Doppler and signal-to-noise ratio on system performance is measured and algorithms developed to improve performance. Our ACDS systems are normally moored to the sea floor with the acoustic elements suspended in the water column. However, one ACDS system has been modified for attachment to a tow frame, and in this configuration it provides a near-ideal autonomous undersea vehicle (AUV) test platform. Each of the ACDS systems provides semi-autonomous operations for up to 78 hours. Custom-designed software is used for onboard data monitoring and signal processing. Back in the lab, advanced signal processing algorithms are applied to the recorded signals to extract the phase-encoded bit patterns and to improve communication accuracy.

INSTRUMENTATION: (1) ACDS buoy systems include three deployed modem systems, a shipboard control station, and wireless local area network (WLAN) communication links. Each deployed modem system includes one acoustic projector (3, 10, or 20 kHz), eight hydrophones, 300 GB of data storage, and three computers. The systems can be moored to the ocean bottom or towed behind a surface vessel. (2) Towed source systems include 3- and 4-ft V-fin towbodies mounted with acoustic projectors, driven by 2-kW power amplifiers. (3) Shipboard-based receiver system includes a custom 16-channel hydrophone array, signal processing electronics, and data monitoring and data recording equipment.

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